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Balanced Ventilation for a Not-So-Old House

The Zehnder ComfoAir Q600 Arrived At My House

You may recall that I bought a ranch-style house a couple of years ago and have been doing some work to improve it.  The house was built in 1961, so it turns 60 years old this year.  That may seem old to some people, but I think it’s actually still young and sprightly!

How leaky is my house?

But home builders in 1961 didn’t pay much attention to making homes airtight.  In fact, they probably hadn’t even started claiming that “a house needs to breathe” because pretty much no one was arguing otherwise, especially in Atlanta, Georgia.  I don’t know what the air leakage in the house was before 2012, but I know it had to be a lot leakier than it is now.  Here’s a little history of the air sealing and air leakage measurements over the past decade.

  • 2012 – My father-in-law, from whom we bought the house, had the attic encapsulated with open-cell spray foam insulation.  It was a pretty bad job, and I’ve got articles and videos on that and what we did to fix it coming this year.
  • 2015 – My father-in-law  had the crawl space encapsulated and some other air-sealing work in the basement done by PV Heating & Air.
  • 2019 – I bought the house and did a blower door test.  The result came in at 6,650 cubic feet per minute with the pressure difference between the house and outdoors at -50 Pascals (cfm50), which translates to 11.3 air changes per hour at 50 Pascals (ACH50).
  • 2019 – Woodman Insulation came in and added more open-cell spray foam insulation (made by SES Polyurethane Systems).
  • 2019 – Blower door test results:  5,220 cfm50, 8.8 ACH50.  That’s 2.5 ACH50 lower than before I had more foam sprayed in the attic.  Nice decrease!
  • 2019 – I had all the soffits, fascias, and gutters replaced and seized the opportunity to do more air-sealing and insulation above the exterior wall top plates.
  • 2019 – Blower door test results:  5,018 cfm50, 8.5 ACH50.

So yeah, my house turns 60 years old this year, but at 8.5 ACH50, it’s not that much worse than the Georgia requires for new homes (5 ACH50).  I’ve tested homes younger than this one that acted much more geriatric, with air leakage numbers twice as high as my house.  And when I get to gutting and remodeling my basement, I’ll make it even tighter.

Ventilating dehumidifier or enthalpy recovery ventilator (ERV)?

Until recently I hadn’t decided which way I’d go for ventilation.  We have an Ultra-Aire ventilating dehumidifier at the Energy Vanguard office, and I like that approach.  I’ll be adding some dehumidification later, but I’m going with an enthalpy (or energy) recovery ventilator (ERV) for our mechanical ventilation system.

And which ERV am I getting?  Actually, it arrived yesterday, and it’s the Zehnder ComfoAir Q600.  Most people who deal with high-performance homes will tell you that Zehnder makes the most efficient and elegant mechanical ventilation systems.  It’s the dream system for people who know residential ventilation.

And it’s not cheap.  I’ll be honest.  I’m not a rich guy and am behind on saving for retirement (not that a young person like myself is thinking about retiring) so even though the Zehnder ERV is a the Rolls Royce—sorry, the Tesla—of ERVs, I might not have gotten one on my own.  But the folks at Zehnder America gave this system to me, knowing that I’d tell you about it and you might decide to get one for yourself.  There’s my disclosure.  Still, ask around and you’ll find to be true what I said about Zehnder being the most esteemed name in balanced ventilation systems.

Balanced ventilation arrives…sort of

Yesterday three pallets of Zehnder ERV equipment arrived at my house.  You can see some of it in the lead photo of this article.  The ERV itself will go into my basement mechanical room, next to my heat pump water heater.  Since I’m going to gut and remodel the basement, I’ll be using the ERV just for the main floor at first.  I’ll run the ComfoPipes up to the encapsulated attic.  Use the ComfoTubes to distribute the ventilation air to the rooms.  I’ll have boost switches to ramp up bathroom and kitchen exhaust when we need more ventilation.

Here’s a little video I made of the “unboxing” after I got the delivery yesterday.

It’s going to take me a little while to get the system up and running because I’ve got a bunch of people waiting for a book they pre-ordered and that I have to finish writing.  (Here’s my book update page.)  But I’ll provide occasional updates here as things progress.

Meanwhile, I’m counting on my young and sprightly house to help keep me young and sprightly.  Because I am a mere seven days away from turning 60 years old myself!


Allison Bailes of Atlanta, Georgia, is a speaker, writer, building science consultant, and founder of Energy Vanguard. He is also the author of the Energy Vanguard Blog. You can follow him on Twitter at @EnergyVanguard.


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This Post Has 16 Comments

  1. Dr. Bailes, what do you think about simple fresh air supply fans, like Broan FreshIn or Panasonic WhisperFresh, routed into the HVAC return plenum in 3A climates?

    I really want fresh air brought into my tract house, due to very high CO2 levels (easily above 800 ppm) that I’ve observed.

    I have a qoute for Ultra-Aire install, but I don’t feel that the humidity is excessive and have concerns about how long such a complicated piece of machinery can survive in my attic which easily hits 130F during the summer.

    1. JM, balanced ventilation, with equal supply and exhaust, is usually better than supply-only. Supply-only ventilation can work in the Southeast and there are many houses with systems using that approach. Mostly they rely on the air handler’s blower, not an external fan. The fans you mention along with the Air King QuFresh can be set up to introduce air directly into the house or the way you mention, sending the outdoor air directly into the return side of the heating and cooling system. You’ve got to be careful either way. The Broan fan you mentioned goes up to 180 cfm, which could cause problems with your heating or cooling capacity or add too much air for your duct system. Putting the air straight into the house can lead to comfort problems. An ERV, with its heat and moisture recovery, solves the latter problem and separate ducting solves the former.

      Yeah, hot unconditioned attics are hard on equipment. Talk to the folks at Ultra-Aire, though, and see what they say.

      1. You mentioned in a previous post (about the undersized minisplit…comments are closed on that one) that the attic had some spray foam, but you did more and it was open cell. Also you mentioned that there were two air handlers for your system. My questions: If you had started with the attic being vented would you have changed to invented with closed cell foam instead of open? 2nd question….how do 2 air handlers work with one compressor? Can that be done with a traditional unit (a non-variable speed compressor)?

  2. For ventilation, the industry seems to be shifting to best practices of dedicated return for the dehu/ventilator, connect ventilator supply to the main house HVAC supply. If you connect that way, can the ventilator run at the same time as the main HVAC can, or does it need to be locked out when the main HVAC is running?

    As a follow up blog post, I’d love if you’d spin a few words on pros and cons of various ways of connecting ERVs/whole house dehumidifiers to the main system and why each manufacturer seems to have its own preferred install methods. e.g. return to return, dedicated return, return to supply etc.

    1. Matthew, the best practice is completely separate ducting for ventilation systems. You have to make sure the duct system can handle the total air flow and that you don’t cut your heating or cooling capacity by overwhelming the system with outdoor air (mainly a problem with straight outdoor air). Here’s a great article by David Treleven of Therma-Stor, the maker of Santa Fe & Ultra-Aire dehumidifiers:

      Ductwork for ERVs, Dehumidifiers, and Forced-Air Heating Systems

      As I install my new Zehnder ERV, I’ll be posting a lot on ventilation in general, ERVS and HRVs, and ducting. And as we head into summer, I’ll be writing a lot about dehumidfication, both as part of a ventilation system or just for the indoor air. Stay tuned!

  3. So, what do you think of the Aeroseal folks, for minimizing your air leakage? It sounds like you’ve done everything reasonably possible, but if you wanted to reduce your leakage even more, that black magic would do it… though installation would require you to basically move everything into a PODS or something.

    1. Jason, I think Aeroseal is a great product. There are more reasons for using it than the one you mentioned, though. I’ve heard of some contractors using it to save time for their workers who need to move on to the next job as quickly as possible. It also helps ensure they meet code requirements for duct leakage. And in existing home,s you can’t always reach all the ducts to seal them by hand.

      1. I’ve only come across Aeroseal a few times in discussion, but those times were always referring to structures that were already tighter that 8.5 ACH50. Can Aeroseal reasonably be used to bring something like that down substantially or is there a ceiling to where Aerogel can be used?

  4. Hi You’ve probably heard this before but I fail to see the rational to seal your house all up and then have come up with ways to dehumidify.

    1. Bill, air sealing a house reduces the need to dehumidify in a humid climate because you keep the humid air out. Then you mainly have to deal with the moisture generated indoors and what you bring in through ventilation. An ERV exchanges moisture between the exhaust and supply air streams, so it brings in less moisture than other ventilation methods. Once you’ve done those things, handling the remaining humidity is easily done with the air conditioner on days that are hot enough. That just leaves the days when the temperature is moderate and humidity high, which I wrote about last year in this article:

      The Perfect Weather for a Dehumidifier

  5. Professor Bailes,
    When you said “The ERV itself will go into my basement mechanical room, next to my heat pump water heater” … is there a latent heat benefit of placing it beside your heat pump water heater?

  6. Hi Allison,
    Just curious if you considered the ComfoFlex vs. the ComfoTube and why you went with ComfoTube. We’ve switched over to all ComfoFlex up here in Ontario to meet the building code requirement for non-combustible ductwork. Is that a concern in Georgia?

  7. Purchased the Awair unit and love it. Now for a more complicated scenario/question: I am questioning the need for an ERV or HRV in a Southeastern climate. Firstly, I don’t agree with ASHRAE using exhaust fan to make house go negative and use leaky house infiltration as source of fresh air. (too many noses on the house) What I am using is a totally sealed and conditioned attic space, blower door <1 ACH50, dedicated 70pt Aprilaire dehumidifier, QFAM 6" makeup air duct 120cfm directly into conditioned attic space for dilution/blending prior to being introduced into living space using intake on dehumidifier. (one main nose on house). This makes house slightly positive with some exfiltration via bath vents and the low number of small holes in house envelope. I have never liked the idea of a house going negative as you have no control over what is being breathed in along with the risk of hot humid air meeting up with cold air-conditioned air, resulting in condensation in places you don't know about (otherwise you will have fixed them). Please advise where I am going wrong here.

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