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The Contractor’s Fear of Third-Party HVAC Design


What if a builder refused to build from plans drawn by an architect? What if a tile installer refused to implement designs handed to them and instead did their own thing? What if an HVAC contractor told a potential client they wouldn’t install a system designed by a third party to ACCA protocols? One of those questions is more real than the others. Of course builders build from architects’ plans and tile installers don’t throw out designs they’re asked to implement. But third-party HVAC design is a different animal.

The benefits of using a third party for HVAC design

We do third-party residential HVAC design here at Energy Vanguard. Andy Bell runs that part of the company and is a true master of the art and science of heating and cooling load calculations (ACCA Manual J), equipment selection (Manual S), register and grille selection (Manual T), and duct design (Manual D). That’s pretty much all he does these days.

Our clients are architects, HVAC contractors, home builders, owner-builders, and homeowners having their dream home built. When they hire us, they do so for several reasons. They want:

  • Their system sized using load calculations rather than rules of thumb
  • Help deciding among a broader set of options than most contractors offer (e.g., conventional equipment, mini-split heat pumps, ductless, ducted…)
  • The design done by a company that doesn’t make money off the sale of the equipment

We’re one of a pretty small group of companies that do third-party design. Mostly what happens is that HVAC contractors make the decisions about what equipment to install, what size it will be, and how to get the heating and cooling distributed. Sometimes they do actual design, using the protocols of the Air Conditioning Contractors of America (ACCA). Mostly they use other methods, usually rules of thumb.

The problem with rules of thumb is that they’re unreliable. Using the industry standard ACCA protocols, when they’re done accurately, doesn’t mean you’ll never have any problems, but it gives you the best shot of designing a system that will work. We’ve done hundreds and have had only a handful of former clients come back to us with problems. In those cases, we’ve been able to help them figure out what’s going on and fix the problem.

The (occasional) difficulties of third-party HVAC design

Sometimes we have a different kind of problem. We usually work remotely and never see our clients. They hire us. We provide the HVAC design documents. They use those documents to hire a contractor (in the cases where they don’t already have one). And that’s where things can fall apart.

One thing that happens is the client provides our design documents to a contractor, who says, “I’m not going to install that. I didn’t design it.” Or worse, they take a look, see what size we’ve specified for the air conditioner, do a quick calculation in their head using a rule of thumb, and say, “This design is wrong. It won’t cool your house. You wasted your money hiring them, and I’m not installing that.”

Most of the time we’re able to work with the client and the HVAC contractor to overcome those initial objections. Occasionally, though, every single contractor the client talks to is dead set against using our design. And because they meet with the client face-to-face and we’re only a voice on the phone, the contractors have a little extra sway.

The contractor’s fear

Going back to those initial questions I asked, builders don’t have a problem building from an architect’s plans and tile installers don’t have a problem implementing the designs of others. But HVAC contractors aren’t used to being told what size equipment to install and how to run the ducts. And they have legitimate fears.

If the equipment sizing and duct design are significantly different than what they’re used to installing, they’re afraid it won’t work. When that job is finished and people are living in the house, who are they going to call if the system doesn’t work? Well, the first call probably goes to the builder. Then the HVAC contractor. Then the third party HVAC designer, if the previous two calls didn’t get the desired results.

So the HVAC contractor is ahead of us in the accountability line. They look at a design that’s different from what they’re used to installing, and that extra accountability is what scares them.

How do we fix this?

I’m not writing this to throw HVAC contractors under the bus. Yeah, there’s plenty of bad workmanship and uneducated contractors out there, but the HVAC industry needs a revolution. Contractors have three big areas of responsibility when they get a job:

  1. Design
  2. Equipment
  3. Distribution

I’d say the only one they do OK on is equipment. Yes, there are contractors who do all three well, but they’re in the minority. The majority of contractors skip over design and do a pretty bad job on the distribution side. I’ve written plenty about the distribution side in this blog. Today my focus is design.

Where I’d like to see us get to is to have a relationship between third-party HVAC designers and HVAC contractors like that between architects and builders. Architects and builders are both licensed professionals, so one part of the answer may be to require licensing for third-party designers. I’m not convinced that would solve the problems, though. If licensing were the answer, the contractors — who have to be licensed in most places — would already be doing everything properly. And my friend Kristof Irwin of Positive Energy in Austin, Texas is a licensed engineer who faces the same kinds of problems.

My crystal ball is a bit foggy right now, and I can’t see where this ends up. Maybe the answer is time. As third-party HVAC design becomes more common, the difficulties should diminish. Maybe it’s educated home buyers. I’m doing my part here to help with that. Maybe it’s something structural, like licensing. I don’t know.

What do you think?


Related Articles

Air Conditioner Sizing Rules of Thumb Must Die

The Basic Principles of Duct Design, Part 1

Why Won’t the HVAC Industry Do Things Right?


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This Post Has 64 Comments

  1. Should be easy to rectify.
    Should be easy to rectify. Install failures are the responsibility of the HVAC company. Performance issues are the responsibility of the designer. Of course verification as to which is responsible is required.

    My guess is that the push back occurs because some installers do not religiously follow the prescribed methods for running duct (especially flex duct) and balance it by using oversized equipment. It’s a win-win for the installer because they save money (i.e. labor) by cutting corners on duct install while simultaneously make extra money by selling oversized equipment. Are installers able to give up that extra revenue in an industry with narrow margins and cutthroat pricing?

    Maybe if designers were able to certify the install they’d let the HVAC company off the hook?

    1. JC, your second paragraph

      JC, your second paragraph pretty much nailed it. Those are exactly the kind of contractors we get pushback from.

    2. All “professional” have their
      All “professional” have their “rat” jobs. We have some mechanical engineer that lack knowledge and architects who know very little about HVAC, Oh lets not forget the $4.50/square carpenter who morphed into a “professional home builder”. Come to Chattanooga, we have some “professionals” needing tossed under the bus! And yes, some “licensed” HVAC contractors needing few tread marks. However, We all are wanting the same best-practice installations. But not more governmental control. Licensing is not a license to say it will be done correctly. Its almost laughable. Nothing is as good as field experience. Ignorance is not limited to the HVAC contractors.
      There a web-site I use to go and see the “wall of shame” pictures. We should have one for architects, HVAC designers, mechanical engineers, home-builders, insulation contractors and code approving officials. My advise would be let capitalism work. And no am not talking about the BBC or Angie’s List. Lets get back to Buyer Beware. There are great companies HVAC contractors still doing great jobs. We just need everyone involved in a project to care more for excellence and helping others involved in the same project to watch each other backs. The Buyers get the benefits and we all grow to a better understanding of home-building as things become more complex.

      1. Yes, having a license is no
        Yes, having a license is no guarantee of quality of work. But it does show that they have at least met whatever requirements there are for it. No license means no way to know if the person has any relevant experience or education or not. It can also make the license holder more accountable in some situations.
        The problem with Buyer Be Ware and relying on Capitalism is that it assumes the buyer has pre-existing knowledge about the work to be done and the contractor who does the work. Often people don’t know a bad job until someone else points it out to them.
        Here in North East New Jersey, it seems contractors just don’t care. My boss put it this way…there is too much work and not enough contractors (in any discipline). They don’t care about doing a half-assed job since there will be no loss for work and they rush it to get to the next gig. And in my experience, even the people who want to do a good job fall short since they are rushed due to the workload.
        A foremean for the roofers (multi-state company that specializes in communities etc.) who put a new roof on my condo couldn’t understand when I was explaining to him that how they did the dryer exhaust is against code and created a fire hazard on top of the fact that half of the moist air is blowing into the attic. I gave up and said never mind, I’ll fix it my self. The engineering firm that was acting as project manager, I emailed the engineer and explained that due to the size of my attic, the minimum net free air of the roof vents is below code. He said it is better to have a 50/50 intake from the soffit and output from the vents than to make the vents bigger and unbalanced. I replied back that the soffit vents run the entire length of the roof plus extra on the gable and have more than a dozen times the required area already. Not to mention the 1/300 minimum code requires is based on a peaked roof and my section is a lean-to shape which has triple the air volume as the one used for the code calculation. And that they have the software to properly calculate the fluid dynamics of a passive ventilation system. I got ignored at that point. Both companies are doing extremely well regardless of being incompetent. Both of them are still more competent than the company that did my original HVAC system and insulation which is still doing very well also. And I’m barely getting started. Capitalism isn’t working. Buyer be ware isn’t working. Relying on companies and people to do the right thing and have integrity isn’t working. I’d say we need more inspections to keep people honest but the inspectors are overworked and suffer from the same issues.

  2. My problem, as an HVAC
    My problem, as an HVAC contractor, seems to be somewhat opposite to what Allison asserts above. It’s not that I disagree with Allison, rather it is just that the quality of 3rd party design in my area is lacking. We nearly always resize downward based on our own load calc.

    One we revamped recently substituted a single 3 ton system for 2 two tonners. Along the way we raised system SEER and EER and deployed a 3rd temperature control zone.

    Another earlier this week – ductwork and air handler entirely within conditioned pressure / temperature envelop, but mysteriously the ducts still accounted for 3300 Btuh of sensible and latent load.

    A third problem – a duct design may look good on paper but the design fails utterly to account for the realities of the structure. This gets us every time in multistory homes. The truss cavities and other structural elements as well as needs of other trades preclude building the duct system so neatly depicted on paper. Until Mechanical / Electrical / Plumbing plans become the norm in single family residential, the situation will continue to be garbage in, garbage out.

    1. Curt, that’s a great point.

      Curt, that’s a great point. There are certainly no guarantees that everyone doing third-party design knows what they’re doing. Even hiring a licensed engineer isn’t the answer because many of them work almost exclusively on commercial projects and don’t know residential. If all HVAC contractors were as knowledgeable and conscientious as you, we wouldn’t be having this discussion…and we wouldn’t have a third-party design business.

      The integration of the ducts with the structure is a huge issue. We try to get as much detail as we can about the framing and work with the builder and HVAC contractor to make sure our design does actually work in the building.

  3. Manual J and D calcs need to
    Manual J and D calcs need to be verified and tested when installed. The problem is the enclosure values are not verified when installed as designed. If the designer relays on a value and it is not provided, the the house will have problems. Enough values not installed as designed and “FAIL”.

    Because most homes have lousy enclosures, most HVAC contractors have not seen it work, only failures.

    The other problem is wanting 70 degrees F inside when the outside temp is 105 and the summer design temp is 98.

    Unreasonable expectations
    No experience with properly installed as designed enclosure
    Code enforcement believing their job is life safety, not durability or energy efficiency

    1. All good points, John. Plus,

      All good points, John. Plus, things are changing rapidly with codes and now we have new kinds of equipment (mini-splits) and requirements for ventilation and… A lot of moving parts here.

      1. When I first started in the
        When I first started in the HVAC field, the only requirement I needed to meet was being the lowest bid. I also found out that I was held responsible for every failure of the building enclosure – bonus rooms over garages were big problems. What I did was become a building performance expert. Now I will not take on a new construction project without the envelope being air sealed using a blower door to find the leaks and sealing them up prior to sheetrocking. I started making houses exceed PH leakage standards before I had heard of PH. (It is the air sealing that makes PH perform so well, not the excessive below slab insulation) I have had great results with this approach with hardly ever a complaint.
        Yes, I use manual J and manual D. If the building inspector enforced the code, every house would have the reports from manual J filed with the BD or there would be no CO issued. However the real problem facing HVAC contractors is poor envelope performance, after all it is a small minority of builders who do not still believe that a house has to breath through its skin (a hold over from the early days of tight buildings without mechanical ventilation and sick home syndrome) The problem is HVAC contractors have to work with all types of construction, and since the HVAC contractor is not supposed to talk about the building enclosure or have any opinion about building performance, (I have been told “get back in the basement” more times than I can count) he has to assume all building perform poorly and design for that. After all he is the one that is responsible for performances of the home and the comfort of the occupants (bonus room over the garage) and if the HVAC contractor specializes in ground source heat pumps is also responsible for energy use. The answer it to get the building envelope consistently better so the HVAC contractor does not have to protect himself with excessive equipment.

    2. The idea of a “design
      The idea of a “design temperature” is based on heating/cooling degree days. Temperatures exceeding the normal temperature is temporary and only for a few hours. Designing for extremes leads to oversizing equipment resulting in short cycling most hours of operation. Educating the customer is an important part of indoor comfort.
      Instructing them of proper use of a setback thermostat helps too. When away from the home most of the day allowing the indoor temperature to rise or lower saves them real dollars but to expect indoor comfort after entering the home is unrealistic unless the t-stat is set to cool/heat about a hour before opening the door after a hard day. Every indoor item has gained/lost heat and needs time to adjust.
      Running flex ducting; I use to tell my installers to think of the ducts as a highway they are driving on. Sharp curves at high speeds is a bad idea and hills require more energy. Small roads require a slower speed than a freeway.
      Using Manual T! What the heck! “I have been installing air conditioning systems for over 25 years and you just started!” Well, this grille will throw the air against the wall and rebound plus it is quieter. Yours will prevent the air from ever reaching the wall. “I have always used this grille and no one has complained!” “Except you!” Oh yes, typical conversation.
      Something else that bugs me; few if any HVAC contractors offer to do a general visual inspection of the system. Here is a link that will give the open minded contractors ideas to build extra business.
      I welcome your good/bad/ugly comments, you want hurt my feelings.

      1. @Joseph, good comment, but
        @Joseph, good comment, but one small correction… the outdoor design temperature is not based on degree-days, which reflect daily variations from a base temperature (typically 65F), but is based on the 1 percentile and 99 percentile hourly temperature norms over 30 years. For example, if the cooling design temp is 95F, that means on average, 1 percent of the hours can be expected to be above that temperature.

        The reason this works is not just because excursions above the design temperature are short in duration, but because the mass and insulation of a house creates significant thermal lag. The 1st/99th percentile temperatures are appropriate for most homes but when a home has a lot more mass and/or insulation that average, it makes sense to use the 2 percentile cooling temperature. ASHRAE publishes 0.4%, 1% and 2% cooling design temps, and 99.6% and 99% heating design temps for thousands of locations worldwide.

        1. Thank you Dave. When I did
          Thank you Dave. When I did load calculations the software utilized degree days for the local area utilizing the local Airport weather station. Your referred to 65 degrees as the base which I understand to be correct along with data collected over 30 years. I admit I am not ASHRAE certified but do have some understand of load calculations. If and when I secure a new position in the industry I will be very interested in reading your referenced material. I had to take a sabbatical. Ps, I believe Manual J has a chart in the back of the book. It has been a few years.

  4. Your analysis is more of an
    Your analysis is more of an apples to oranges vs apples to apples comparison. The architect is met face to face, worked with closely and is likely involved in seeing the construction take place. Even if the HVAC contractor liked your design, would he worry about how the contractor is constructing the envelope which definitely would affect the performance of the HVAC system.
    My suggestion is when a potential customer contacts you, ask to have some initial direct contact with the GC. Make a phone call and then email an introductory packet on who you are. Get a rapport established with the GC first, then do the design for the client and stay in communication with the GC.

    1. Good point, Bob. We always

      Good point, Bob. We always offer to work with the builder and HVAC contractor to make sure they get what they’re paying for. Sometimes, though, they don’t have either a builder or HVAC contractor when they hire us. Most of the time, as I said in the article, everything still works out fine. When our client is the builder or HVAC contractor, the chances for things going south are really low because once they hire us, they’ve bought into the rationale for third-party design.

  5. In a resent HPAC Engineering
    In a resent HPAC Engineering article, computer analysis software can be used to validate HVAC design. The software can be used as a third part verification. The company featured in the article was SIMSCALE. However, I don’t think the individuals you are referring to would use this tool either, the fear of the unknown!

    1. Gary, yeah, I think you’re

      Gary, yeah, I think you’re right that, as appealing as it sounds to have software that could verify a design, the contractors we have difficulty either wouldn’t use it or wouldn’t believe it.

  6. Perhaps a better approach
    Perhaps a better approach would be for the HVAC installer’s plan to be third-party reviewed. Consensus between the contractor and designer would be based on the best of both worlds. I fully understand the jobsite complexity, which often dictates how and where ducts can be routed. I also understand the benefit of a less biased designer specifying duct and register size and placement.

    The difference between the architect and the HVAC designer is the wet stamp. The architect or engineer takes responsibility when they stamp their plans. The HVAC designer should have errors and omission insurance but probably isn’t specifically licensed by the State to perform his or her calculations and to specify equipment and duct sizing. That, of course, changes if a PE stamps the duct plan, but this would be very rare.

    The difference between the tile installer and the interior decorator is even more complicated because taste and artistic appreciation are the driving factors, not strictly a science-based design.

    Circling back, whether the HVAC design starts with the contractor or a third-party, communication and consensus are critical to getting the job done right.

    Build it Tight and Ventilate Right!
    Every high performance home should be well air-sealed and properly ventilated. This doesn’t mean a timer on the bath fan. Proper ventilation is really easy but needs to be carefully considered during design and construction of the hVac system.


    PS: I was an HVAC/HW contractor for 15 years. The HW is hot water. We sold about 10,000 water heating heat pumps and over 4,000 heat pump and conventional systems, all of which were sized using ACCA Manual J… hand on a spreadsheet before we had PCs.

    1. All good points, Mac, as

      All good points, Mac, as usual. I don’t think having an engineer’s stamp on the design would change much because the contractors who object to third-party design probably would have the same objections.

  7. Allison–You and I agree that
    Allison–You and I agree that the state and reputation of the residential HVAC industry is not-so-good when it comes to system design but, as stated multiple times in the comments above, residential and commercial construction are two completely different animals. Not to make excuses (and certainly not to let cruddy contractors off the hook) but there are so many variables that a residential HVAC contractor has to deal with (customer whim regarding desired indoor temperature, changing framing plans, a lack of understanding of envelope sealing on the part of the contractor) that most are understandably nervous to implement an outside design when that design was calculated and drawn long before the first nail was driven. I truly wish there was a good way to implement (even force) better design and to use third party designers to help produce a better system but decisions that affect design are often made “on the fly” in the field by folks who simply do not understand the repercussions of their actions. When the question of who is liable for the poor implementation of a well-crafted design starts to roll down hill, invariably, the HVAC contractor is going to take it in the neck. Unfortunately, without the architect and the contractor being fully invested in the process (and at least partially liable for the havoc they create after the HVAC design is agreed upon), you will have a tough row to hoe convincing HVAC contractors to climb on board the train. As I have often heard, it takes a village…

    1. Jake, I agree. In the vast

      Jake, I agree. In the vast majority of our jobs, we don’t have a problem because either the contractor look at our design and understand it or we work with them to understand it and we modify as necessary when they provide us info from the field. But those few jobs that don’t work out bother me. And then there are the jobs we never get because a potential client runs into this resistance before they hire us.

      Yes, it takes a village, as you say. When we’re more involved with the other villagers, the outcomes are good. When a client runs into a contractor who doesn’t understand the design and doesn’t want to understand it, we don’t get to be part of the village and things don’t always work out so well.

    2. As an Energy Star builder in
      As an Energy Star builder in Climate Zone 3 we have faced this issue for a number of years. Simply put, most HVAC systems in our area are over-sized in tonnage, undersized with returns, not balanced as to air flow, and have ducts that leak as much as 30%. All of this by licensed HVAC contractors! I have a couple of installers that have learned to do it right, along with me and get duct leakage down below 5% and have comfortable conditions throughout the home, even on the 105 degree day with a 98 degree design! Of course a good building envelope is the first place to start but properly placed high efficiency vent registers, properly sized equipment and placed returns along with transfer ducts or grilles in all bedrooms are the key to having a design that works, most of the time at one half the tonnage that Bubba wanted to put in if I allowed them to do so!

      As for the builders involvement with duct design, they need to be taught how to plan for the structural elements that allow for duct placement in the correct locations along with returns for the equipment. It’s no longer acceptable to throw up a bunch of beams or joists and let the HVAC contractor show up to figure it out! I has to be planned in the beginning and if a builder doesn’t educate himself or herself in this type of planning then they ought to find something else to do as a profession. I have used a third party designer separate from my installers for quite some time now. If I get push back from an installer then they know they won’t do the next job for me. In my world of custom home building I can’t just blame the HVAC sub and satisfy my customer’s complaint. That gets me nowhere. The fact is, knock on wood, I haven’t had those complaints in a long time, because right sizing works AND the beautiful thing about it is that it not only provides the comfort but at a fraction of the cost in the energy bill as well!

  8. The joy of our integrated
    The joy of our integrated approach is that we take ownership of verifying both enclosure R-Values and enclosure infiltration.

    I explain that while we furnish and install some of the best HVAC systems around, we will have trouble dehumidifying both the home and the surrounding neighborhood.

    1. High humidity left in a tight
      High humidity left in a tight home sets the homeowners up for a muggy feeling that sends them to the t-stat in an attempt to get a cool feeling. Consider upsizing the indoor coil and slow the air down allowing more exposure to the coil for water removal without kicking water down the supply plenum.
      Tight homes must have ventilation too. It is a head scratcher but a tight envelope traps gasses of every kind creating a hostile living space. Occupants become ill more frequently and feel groggy in the morning. In addition, if gas appliances are used there is an increased possibility of chronic CO poisoning. Low levels of CO may not be detected by a typical CO monitor. However, CO can be absorbed into the bloodstream and mimic health conditions.

  9. Have you ever been on a job,
    Have you ever been on a job, any job in which your boss told you do something a certain way. The boss left for the day. Finally you get around to working on the project and what your boss told you would not work. (enter any reason you want here.)

    The reason I say this for the same reason about a often quoted old wives tale that reads: ‘Too many cooks in the kitchen, spoils the broth.’

    Certainly there are famous kitchens in which there are more than one cook. But do they have their own separate tasks or dishes to prepare?

    Getting back to the HVAC design problem is rarely do you have a HVAC boss, Architect, Designer or other involved in ‘actually doing the work.’ If they did then why would you call them HVAC installers? It’s very rare to find an HVAC installer that can trouble shoot an HVAC system. They only know how to ‘install’ a piece or in new construction all the pieces that make up a HVAC system. Nothing wrong with that by the way as people in this industry have to start somewhere. I am just trying to describe a complicated area that is rarely understood completely.

    The other part is money distribution or who is paid what for the job they do. It was noted somewhere above that margins are razor thin… which should not be marginalized. So as you would suspect the boss — what ever you want to call him is paid proportionately more than the ones actually putting the system in to the design specifications that were quoted.

    Because pay is so low for pretty much any construction trade and the boom and bust cycles the residential construction goes thru, even if you could find the skill how could you keep it with low pay. Remember — razor thin margins.

    Then should the installers mess up the installation due to lack of skill among other pitfalls to immense to list here, whom would be the one to find the problem of the installation. I’ll give you a hint: It’s not the boss… at least rarely speaking. Typically this is where a HVAC technician would enter the fray.

    Now again due to tight margins and low skilled installers you can only imagine how hard this HVAC technician would work at correcting problems with installations. The thought that performance could only be effected by design? Uh no, forget that. There are many things that can cause poor performance from design to improper installation.

  10. Allison, interesting article
    Allison, interesting article and discussion. I do wish you would elaborate on whether/how you would design using mini-split technology. Mini-splits look to me to be much more of an appliance than ordinary residential split systems, and with an appliance the quality guarantee is much more in the factory than in the field.

    Ordinary residential split systems are almost an engineering project as I see it, with many more ways to go wrong. And the people installing are not usually engineers, and often not suited to solving engineering problems.

    Could you design a mini-split approach to any house brought to you? I wonder if you could explain the tradeoffs if adopting such an approach. Thank you.

    1. M.Johnson wrote: Mini-splits
      M.Johnson wrote: Mini-splits are “…much more of an appliance than ordinary residential split systems, and with an appliance the quality guarantee is much more in the factory than in the field”

      For 1:1 ductless mini-splits, that sounds about right. I can’t speak for Andy & Allison, but you raise an important point. An all-ductless system is rarely a good option for new construction. In a retrofit scenario, it may be the only option, but whole-house ductless necessarily imposes compromise.

      In a code-built home, putting a head in every room with an actionable load can get crazy expensive. More than that, the smallest heads have way too much capacity for most rooms, even at minimum speed. Single-zone ductless can work in a super-efficient home in a cold climate, depending on room layout and owner’s willingness to accept significant room-to-room temperature differences. That may not be a problem if homeowner prefers cooler bedrooms.

      In cooling dominated climates, you gotta deliver supply air directly to the bedrooms. Some Passive House designers learned this lesson the hard way by relying on a fully ducted ERV to indirectly distribute supply air from a centrally located head. It doesn’t work like that.

      For low-load homes, a ducted mini-split (sometimes in combination with a ductless head in the main zone) is often the best solution. But that comes with the same design/install challenges as a conventional system.

  11. Allison, I can share my
    Allison, I can share my current experience that shows the dilemma of the “educated home owner”. I have spent hours reading your blog for our new home construction and would like to thank you for educating home owners (though sometimes I wish I had stayed unaware and ignorant – less headaches … ;-).

    After the Manual J (done by 3rd party HVAC design company) was finished and we wanted to move on and select systems, but now I am stuck between the recommendations of the HVAC designer and the builder.

    a) Builder suggests to put in their standard equipment which is a dedicated 16 SEER single stage unit + gas furnace for each floor based on the Manual J+S+D from the designer. He wants to keep it simple and if I want to spend more money make both of those units 2 stage compressors.

    b) The designer suggests to go with the fancy solution: Lennox two stage heat pump with variable speed air handler and Harmony zoning system (3 zones – 1st floor, 1st floor master, 2nd floor). And based on reading David Butler’s articles on heat pumps and high performance homes and your articles on zoning that seems like a good choice. BUT will it work if the HVAC contractor installs such a system for the first time?

    Do you have any experience on how to tackle such situations? I was very excited about the whole HVAC design being high quality and now find myself learning towards chickening out and going with the “standard” (at least it will be sized correctly) just to play it safe.

    1. Rob,

      3 temperature control zones from a two stage heat pump and variable speed air handler is quite doable. In fact it is quite a sweet spot for our company. We do that with generic (Honeywell) controls rather than proprietary manufacturer controls for simplicity and cost savings. That said, a contractor new to zoning might not be the best fit for a proprietary 3 zone project right out of the gate.

      It has been awhile since I’ve considered Lennox Harmony. My vague recollection is that it ranks up there with Carrier’s Infinity system, and is probably priced to match. We charge an extra $400 per zone for Infinity vs Honeywell zoning. Is it better? Yes. Is it worth an extra $1200 for 3 zones? Hmmm.

      A separate 3rd zone for the master suite is a sweet upgrade, IMO. In your shoes, I’d circle back to the designer advocating the Lennox Harmony system and ask if he / she is sufficiently familiar with that particular system to aid a favorable outcome despite a rookie contractor.

      You didn’t mention your climate zone. That affects the suitability of heat pumps vs gas furnaces. A hybrid solution is likely an option, albeit at more cost and complexity. Unit energy costs of gas vs electricity are worth considering as well.

      Examine any proposed zoning design for presence of a bypass damper. These purport to fool the air handler by routing supply air right back into the return. Don’t allow one to darken your door. Presence of a bypass indicates an unevolved zoning designer. Run!

      1. Thanks Curt. I’m in Houston,
        Thanks Curt. I’m in Houston, TX. Gas is very cheap and the builder told me he has not once put in a heat pump.

        A question on the none-proprietary zoning system: Does a Honeywell system still communicate with the blower to set the variable speed and condenser stage? And do the thermostats have to match the Honeywell controllers then for this to work? The builder may be more familiar with this because they sometimes do basic zoning within one floor (Master Suite).

        I think the designer suggested the zoning because the loads are low and two separate units may be too large. For example our cooling bthus are approx. 18500btuh first floor (12500 main and 6000 master) and 12000 second floor with approx. 0.85 SHR. Heat bthus are 20% higher for the first floor and about the same for the second floor. He also said that the gas furnance would need to be oversized and then likely short cycle and make the home less comfortable.

        1. Rob,

          As long as the HVAC system has / accepts staging inputs, typically Y1 for low and Y2 for high, it should be compatible with non-proprietary controls. Finding a small enough furnace compatible with a 3 ton straight cool system may be a challenge.

          1. Thanks Curt! You mentioned to
            Thanks Curt! You mentioned to make sure there is no bypass damper or RUN. The designer told me that he can only remove the bypass damper if we go with the fancy Infinity or Lennox system because the Honeywell system cannot control the blower CFM speed and dumping the full force of air into only one zone will make it loud and drafty. He said he can do a bypass return with a special damper that only activates when the static pressure is too high and some relief is needed. Is that ok or in your words … should i RUN?

          2. A well-functioning 2 or 3
            A well-functioning 2 or 3 zone system may be created using “generic” 24 volt controls WITHOUT A BYPASS using most or all of the following:
            1) Two stage equipment
            2) modestly oversized ductwork
            3) Judicious damper cracking
            4) Managed client expectations

            Bypass dampers often cause problems ranging from sweating, rapid compressor cycling, coil icing, etc. In heating mode, compressor may be subject to excessive discharge pressures and amperage.


          3. Thanks a lot for your
            Thanks a lot for your comments Curt! Unfortunately I can’t literally run because the designer comes with the builder and has already completed the Manual J, but I will forget the zoning and tell him to go with the two separate systems for upstairs and downstairs. This seems like the safest path forward. If we go with a 1.5 ton single stage upstairs and a 2 ton single stage downstairs, the budget might even out compared to the two stage equipment and the zoning control cost.

        2. @Rob, Curt & I must be
          @Rob, Curt & I must be drinking from the same trough. He’s given you excellent advice.

          I’d like to add this: the main benefit an integrated zoning system (i.e., Infinity & Harmony) is that it’s smarter about managing airflow so as to avoid direct bypass (IMNSHO, direct bypass should be outlawed). But as Curt said, a sharp designer can accomplish pretty much the same thing using 3rd-party zoning, doing the things he summarized in his “list of 4” above. Almost 2 decades ago, I designed a single-stage 3-zone system for my previous home without bypass, and it worked well (

          If the builder’s HVAC contractor has trained on Harmony, then I’d go with that. Otherwise, I’d push the builder to hire someone who has trained on Harmony or Infinity. With two systems, your furnaces are likely to be seriously oversized. Keep in mind that MJ overstates heat loads in your climate zone by probably 20% to 40%, assuming your house is actually built to spec. There are several reasons for that, but that’s beyond the scope of this article.

          1. Thanks David! Unfortunately,
            Thanks David! Unfortunately, the designer said a bypass is needed and so since everybody on this page said it should be outlawed plus the builder’s HVAC guy is a small residential company who the builder said is best doing “standard stuff” and he suggested to not make it complicated, I figured better to go with two systems since I cannot change designers or HVAC company as they come with the builder.

            But your comment about the heat load being too high by 20%-40% would mean that my heat loads are less than the cooling loads which makes me think that I should probably push for 2 heat pumps with VS air handlers instead of 2×40,000btuh dual stage high-efficiency gas furnaces (equipment in conditioned space). I reviewed the Carrier 25HBC5 units curves and figure that the heat strips would probably come on just a few days per year, if at all.

            Does that sound right?

          2. @Rob, it’s not just the folks
            @Rob, it’s not just the folks in this blog! Here’s a quote from the Infinity zoning design manual: “Not only does Infinity Zoning not need a bypass, but a bypass must not be used.” I thought Lennox took the same position with Harmony, but I could be wrong. Moreover, California prohibited bypass several years ago (although I understand an exception was added). Maybe you should point your designer to this page.

            As for heat pump vs. furnace… I agree with your assessment, but you said gas is very cheap so I would want to compare the operating costs. Contact me privately for help with that (it’s easy but not at all straightforward).

            BTW, Goodman now makes a 30k 2-stage variable speed furnace (20k on low stage; GMEC960302BNA). And Dettson, a Canadian company, now distributes the Chinook 20k modulating furnace in the US. In your area, I believe the distributor is Southwest Energy Integrators in New Mexico.

  12. We find the most success (not
    We find the most success (not the most perfection, but generally the most satisfaction) with a team-build process that brings Architect, Owner, GC and Major Subs together about 2/3 of the way into the design process. As a third party ourselves, our role is to be an educator and bridge between parties, and let everyone know up front that we’ll be there to help everyone meet clearly stated performance objectives – including review of Manual J… and assumptions, ventilation and performance strategies, building envelope attributes, ASHRAE 62.2 calcs based on actual blower door, duct blaster (even for ducts inside envelope), TAB results, etc. As issues and conflicts are discovered (they are in every project) we then try to resolve them as a team. We advise clients to utilize this process and when they do so early on, we have the best results. If there were a 3rd party HVAC designer involved at any stage, they become part of the team early on. This avoids most problems and solves the ones that emerge. Final thoughts: educating clients BEFORE they get too far into the design (and definitely before construction) sets things up for success – no matter the size of the project.

  13. This is a more complex topic
    This is a more complex topic than it first appears. Background: I have been a builder since 1993. Prior to that I worked in the computer industry for 23 years. I was a service manager during the 70s when that industry was moving from electro-magnetic equipment (switches and relays) to sophisticated dense electronic circuits. My crew consisted of people who could take an engine apart on the weekend, but the new tech was all blinking lights and error codes. They no longer knew exactly how it all worked and they hated it. Almost 40 years now and this is where the HVAC industry is. We no longer rely on 24v AC controls with mercury bulb switches. The skills required are way beyond where many HVAC contractors are comfortable. Now add in Building Science. Sizing and design is much more complex due to ever tighter buildings more precise load requirements. I build hurricane/disaster resistant homes using insulated concrete panels and closed cell foam roof decks. My homes consistently blow close to 1.0 ACH without doing anything special. My goal is to break 1.0. My HVAC systems require multi-speed compressors and handlers in order to control humidity (yes, humidity is my number one enemy all seasons). The culprit here, my friends, is lack of knowledge at all levels of the conversation: contractors, builders, designers, owners, all. HVAC has become the most complex of all the trades and it is due to advances in technology and building science.

  14. As is your custom, this
    As is your custom, this article provides a comprehensive overview of yet another contentious and controversial topic, without one-sided finger pointing or criticism (except where deserved) of stakeholders.

    From the perspective of living with a home, I can’t think of a more important aspect of the finished product than the comfort and economy of well-designed and installed HVAC and, since it’s always about the money, could you estimate, on a percentage basis, the approximate incremental project cost increase due to the services your company provides?

    Going out on a limb here, but if your fees don’t exceed 1%, sounds like a bargain to me and as others have pointed out, emphasizing and accurately communicating the long-term value of that upfront expense (investment?) to all participants would be time well spent.

  15. Steve’s comment, “since it’s
    Steve’s comment, “since it’s always about the money” is spot on. I have been the builder and/or the designer from track-homes to multi million dollar homes. With few exceptions, it is always about the money. Therefore, your first job is to be a salesman and convince someone why they need to spend more money, someone who is not really knowledgeable about what you are “selling”.

  16. I’ve been performing ‘3rd
    I’ve been performing ‘3rd party’ mechanical designs for the past 12 years following a career in R&D. So this topic is near and dear.
    My practice has evolved over the years, to a large extent in response to the challenges addressed in Allison’s article and many of the comments posted. Here’s what I’ve learned…

    First and foremost is the need to educate the client, be it a homeowner, builder, architect or mechanical contractor. Particularly with homeowners, managing expectations is critical. They find me and seek my advice and most have done their research, so I find my clients receptive to my message.

    In the initial consultation, I lay the groundwork for my design approach, explaining such things as the rationale behind the indoor/outdoor design temperatures and the importance of 3rd party verification of envelope specs and duct installation.

    Unlike many other independent mechanical designers, I don’t submit duct drawings. When I first started, I quickly learned that 3rd party duct design is a waste of time and money unless the designer can supervise the install. The problem is that few residential crews know how to build to engineering drawings, and with me being remote, it’s too easy for a crew to revert to what they’ve always done.

    Instead, I provide a performance spec (leakage, total static, air balance) and help my client find a contractor who agrees to meet those specs, subject to 3rd party verification. As long as they get the right amount of air to the rooms without exceeding my static limit, I could care less if they did a Manual D or use a ductulator and a pencil sketch, or whether they go with trunk-and-branch, radial or hybrid. I add several specific requirements that help ensure success. Whenever ducts are located in the floor system, I stipulate that the mechanical contractor must sign off on truss/structural design. (to be continued…)

  17. (part 2) To Rokicki’s point,
    (part 2) To Rokicki’s point, when I interview mechanical contractors on behalf of a homeowner or builder client, I emphasize the team approach for achieving success. I review my design approach, especially anything that might give the contractor heartburn (like ductless returns) and solicit his input on the design, especially brand preference.

    Although I’m not always successful, I try hard to get the contractor to invest in my design approach, so he will ‘own’ the system. Ultimately there must be a clear delineation of responsibility: The mechanical contractor is responsible for equipment and for meeting my specs; the builder is responsible for meeting envelope specs (including air tightness), and I’m responsible for sizing and comfort. On rare occasions, contractors require the owner to sign a waiver to that effect.

    One thing that surprises most people… the load calc itself is only a small part of the design process and is but one of several factors that inform system sizing. By far, the majority of my time is spent on the preliminaries: the initial client telecon, nailing down all the envelope specs (I often drive those decisions for optimal value, typically saving the client more than my fee), digging up local energy costs, and in some cases, vetting prospective mechanical contractors. Interfacing with 3rd party verifiers can also be time consuming.

    My highest value service is equipment selection – especially the *type* of equipment and zone layout. But this typically accounts for the least billable time (I don’t charge for chasing down equipment data).

    This is a tough business and as Allison pointed out in an earlier comment, it has a lot of moving parts. But I do enjoy my work immensely or I’d find something else to do!

  18. As to duct layouts, they are
    As to duct layouts, they are required for permitting new construction in our largest county AHJ. Trouble is, as Dave B notes, they don’t get built unless supervised by the designer. In addition, many are basically abstract art, unconstructible in the real world since no attention was paid to truss configuration and other structural elements, not to mention needs of other trades.

    In our area we are fortunate in generally not having to consider / present multiple system type selections…99% of ours are some variation on split air source heat pump system with a few geothermal and package units sprinkled in.

    We are pretty adamant about load calculation being both cooling dominated and constantly battling humidity. System selection is less about SEER (a marginal predictor of actual operating costs…a discussion outside our scope here) but more about comfort performance, quiet operation, humidity control, and present / future zoning.

  19. I agree with D. Butler
    I agree with D. Butler regarding mini splits not giving as good distribution as a well designed/installed duct system. As to the comment, “Single-zone ductless can work in a super-efficient home in a cold climate, depending on room layout and owner’s willingness to accept significant room-to-room temperature differences.”, maybe not. Building codes require a system that gives an even temperature throughout, “R303.9 Required heating. When the winter design temperature in Table R30 1.2(1) is below 60°F 16°C), every dwelling unit shall be provided with heating facilities capable of maintaining a minimum room temperature of 68°F at a point 3 feet (914 mm) above the floor and 2 feet (610 mm)
    from exterior walls in all habitable rooms at the design temperature.”

    1. Rob: Minisplits work well in
      Rob: Minisplits work well in my small (1700 square feet) house in Maine. With near passive house insulation and passive house air tightness, we get very little temperature variations from room to room. Right now, the outside temp is 19° F. Inside temp is 70 in the kitchen/living/ dining room and 69° everywhere else. 99% design temp is 0°.
      I think the key is a good building envelope. With little heated air leaking out, the interior temps even out.

  20. The insurance industry is
    The insurance industry is starting to look at this from a problems down the road aspect not only with the systems and what they are doing or not but for the air quality issues this causes . We are working on a coupla projects to investigate this with future and not so requirements calling for MEP + Environmental + MSDS + Spacial + Structural parametric models all verified back through the risk management company. Don’t follow the approved models and your EO / GL will be toast with permitting authority notified accordingly . Project example is here

  21. Once again, David Butler’s
    Once again, David Butler’s comment shows overwhelming insight. To wit, “I quickly learned that 3rd party duct design is a waste of time and money unless the designer can supervise the install.” We BS nerds can elucidate, calculate and pontificate 16 hours a day. But getting in the trench and working with Bubba and Earl (B&E Heatin and Coolin) is where putative best practice meets reality. It’s also where you may find your expertly crafted design drawings which have become the floor mat in the F150.

  22. This is so spot-on, we deal
    This is so spot-on, we deal with it more often than not. Very frustrating. 100% agree with this as a key solution: “Where I’d like to see us get to is to have a relationship between third-party HVAC designers and HVAC contractors like that between architects and builders.”

  23. I have a new 1,900 sf home
    I have a new 1,900 sf home with a 75% basement foundation and the remainder is crawlspace. The configuration is 2″ blue board insulation on the interior of the basement foundation, taped and sealed. (Contractor did not insulate the foundation exterior as prescribed so we went ahead with a Building Science Corp design) we then framed walls and insulated them with unfaced fiberglass followed by green board. There is an air space between the blue foam insulation and the unfaced insulation and framed wall. There are two supply drops in the basement with no returns. The crawlspace has a concrete slab floor over poly. The same blue board insulation, taped and sealed on the crawlspace foundation walls with spray foam in the box ends. The crawlspace also has a single supply drop as well as two openings into the return floor joist chase that runs in the crawlspace to pick up return air from the bedroom above the crawlspace. There are air connections between the basement and crawlspace by way of the access scuttle opening (30″ x 30″) as well as the floor joist cavities above the separation wall between the basement and crawlspace areas.

    The crawlspace is considered clean but still concerns me with the return duct openings.

    With the crossover air openings, is it a good idea to have the return openings in the crawlspace area? We have a passive radon system installed and in mid winter (Northwest Ohio) we are going to test to determine if we are going to make the radon system active. The HVAC contractor states he normally installs a register in the return duct and that a conditioned crawlspace should have air pulling out of it.

    I’m also a bit concerned that the blue board insulation in the crawlspace is exposed. We did receive an occupancy permit based on “passing” inspections.

    Any insight and advice is welcome.

    Thank you.

  24. Refer to question about
    Refer to question about return in the crawlspace where the air is “connected” from the basement to the crawlspace.


    Bill Barnes

  25. Bill,
    I am more concerned about the exposed blue board. It is highly flammable with fast flame spread. The presence of ducts in the crawl space makes it part of the conditioned space and the danger of fire even greater. You have to at least spray it with intumescent paint. I recommend only using Dow Thermax insulation when being left exposed as it is listed as a finished wall product.
    Otherwise the moving air through the crawlspace is good. It seems to me that you discribed the crawl space and basement being connected through the floor joist space, so location of the returns is of no real concern. I like to have basements and crawl spaces to have less returns than supply as this will provide slight positive pressure to help prevent pulling radon in. I would close one return. I also recommend sealing between the concrete floor and the concrete walls with high quality butyl caulk to air seal the big crack that opens when the floor cures. This is an easy pathway for radon.

  26. Lloyd,

    I appreciate the quick reply and it seems our concerns are in line with yours.

    I’ll look at the blue foam board insulation closer to see the manufacturers trade and product name to help make the determination on whether there is a need to paint the board for fire / flame spread.

    Thank you.

    Bill Barnes

    1. @Bill, it’s probably DOW, but
      @Bill, it’s probably DOW, but since it doesn’t have a foil facing, it really doesn’t matter which product it is. The only way exposed rigid foam can meet the flame-spread code in that scenario is with a foil facing on the interior side.

      The Thermax product Lloyd mentioned is foil-faced polyisocyanurate. Several other companies make similar products in various thicknesses. You can even get polyiso with a clean (i.e., no writing) white facing and white plastic moldings to cover the seams for a finished look.

      Intumescent paint is typically used to protect exposed spray foam insulation and meet the fire codes. Presumably your insulator applied intumescent paint to the spray foam in your rim bands (box ends)? OTOH, some spray foam products are specifically designed to meet the flame spread reg without the paint.

      I hadn’t considered Lloyd’s suggestion for appling intumescent paint to unfaced rigid foam. Hopefully that will satisfy the building inspector. The alternative would be to install a thin layer of foil-faced polyiso boards over the blue, or cover with drywall.

      1. David, Thank you for the
        David, Thank you for the reply and advice. After I get another look at the foam board I’ll be able to determine the course of action we’ll need to take. We have an occupancy permit and apparently the AHJ signed off on the exposed insulation. He seems to have been more of a drive by kind of guy since there have been a few issues with this build that had he looked he would have identified, like no insulation on the foundation wall before back filling was approved, thus the foam board on the interior of the basement and crawlspace foundations. I’m not sure I can identify the make of the spray foam in the box ends but will certainly get to the bottom of this by contacting the application contractor.



        Bill Barnes

  27. David,
    The difference between Iso and extruded polystyrene is that iso will burn under flame impingement but will not spread the flame and goes out when the impinging flame is removed. (The stuff with foil facing.), but extruded polystyrene will spread the flame quickly and will not go out but will intensify the flame and heat. Most building codes require even iso board to have a thermal barrier. I only know of Dow Thermax, which is a finished wall product (and is available with a vinyl face and matching tape) that is exempt from the code thermal barrier requirement.
    The only foam insulation that code does not require to have a thermal barrier is Dow Thermax because this is the only isoproduct I know of th

  28. Hi Lloyd, Rmax TSX-8500
    Hi Lloyd, Rmax TSX-8500 series, Atlas Energy Shield Pro and Johns Manville AP are all foil-faced polyiso products similar to Dow Thermax. Web pages for these products state they can be used without a thermal barrier. Here’s an example:

    BTW, Thermax has foil facings, not vinyl, and is available with a white acrylic coated aluminum for applications where aesthetics are a concern. Standard Thermax has a reflective foil facings with logos, etc.

  29. David,
    Thanks for the run down of products available for use without a thermal barrier. All foam insulation of any type has to have a thermal barrier.
    Personally I recommend NEVER using extruded polystyrene unless it is buried, like under a slab. It is just too flammable to be safe to use otherwise, even with a thermal barrier.

    1. You are correct of course.
      You are correct of course. What the manufacturers *should* say is that these products “can be used without a *separate* thermal barrier.”

      1. David,

        If you are interested in seeing what our local Chief Building Inspector has replied to me with regarding the use of the exposed Dow Scoreboard, 2″ foam board insulation in conditioned crawlspace (supply and return air duct openings as well as communication with the adjacent basement, I’d love for your opinion on it. If there is an email I can send the reply document to please email me directly and I’ll forward his rebuttal to you.

        At this point I’m at a loss because it seems the information he provided in some ways is contradictory based on the specifics of this particular install.

        Thank you.

        Bill Barnes

      2. @Bill, I’ve reached out to
        @Bill, I’ve reached out to you via email. IRC Section R316 Foam Plastic is quite clear on this. In particular, Section R316.5.4 spells out the specific requirements for using foam in a crawl space. Bottom line: unless an approved thermal barrier is installed as described in Section R316.4 or R316.5.4, the product must have a specific approval related to actual end-use configuration (R316.6). Dow Scoreboard does not have such an approval.

        I’m not sure what his rationale may be but it wouldn’t be the first time a building inspector misinterprets the code (although it’s usually in the other direction)! But this is not something you want to skimp on just because you can. I would cover the Dow board with a layer of foil-faced polyiso or a coat of intumescent paint.

      3. To close the loop on this
        To close the loop on this side discussion, I reviewed materials sent to me by Bill and it appears that Dow has ‘threaded the needle’ to get their extruded polystyrene products (Scoreboard in this case) approved for use in attics and crawl spaces, as well as other building assemblies, without an ignition barrier as specified in IRC Section R316.5.4.3. The specific applications and conditions are covered in ESR-2142. This is surprising to me but I’m happy to admit that I was wrong.

        In a nutshell, certain listed Dow XPS products up to 2 inches in thickness are allowed in crawl spaces without a separate ignition barrier. Use in attics is limited to 1 inch, with further restrictions.

        The UL test (ASTM E84) that accompanied the ESR reported flame spread and smoke developed classifications of 5 & 165, respectively, for most Dow Styrofoam(tm) brand products. These results are well below code-required 25 & 400.

        Interestingly, the UL report included the following footnote:
        “Flame Spread and Smoke Developed were recorded while the material remained in the original test position. Ignition of molten residue on the furnace floor resulted in flame travel and smoke generation equivalent to a calculated flame spread classification of 125 and a smoke developed classification of over 500.”

        Hmm… Seems like ignition of plastic insulation that melts and falls on the floor would be cause for concern? Methinks this a bureaucratic loophole. In any case, I’m still hesitant to specify exposed XPS in a crawl space that communicates with basement and has supplies and returns, as described.

  30. I would NEVER put flammable
    I would NEVER put flammable material, sans thermal ignition barrier, in any habitable building. I include ones for animals.
    It does not matter if the building code allows it.

    I know of a building that burned so hot that the fire department could not put the fire out. I am a life member of the local fire department and I have seen many instances of flammable insulation making it impossible to contain the flames.
    Who can forget the London fire of the high rise burning from the outside? The insulation was extruded polystyrene, and is the reason the fire spread.
    Enough said.

  31. Once again great article!
    Once again great article! Thanks for bringing this up. Keep up the good work

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