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Range Hood Makeup Air: The Basics

A Kitchen Range Hood Sucks Air Out Of A House. Do You Need A Range Hood Makeup Air System To Go With It? [photo By LG, CC2.0]

Kitchen ventilation is critical to having good indoor air quality in your home.  Cooking, as the research shows, produces a lot of indoor air pollutants.  The best way to deal with that is to have an exhaust ventilation system that removes those pollutants at the source.  But when you exhaust air from an airtight house, you can induce some serious negative pressure.  So what’s the solution?  Do you need a range hood makeup air system?

As part of our residential HVAC design services at Energy Vanguard, we design makeup air systems for some of our clients.  To do that properly, we’ve had to dig in on this topic to find the most appropriate solutions.  Here’s a brief summary of what you need to know about range hood makeup air systems.

A cfm out…

The first thing to know is that we’re talking about air.  Yeah, Alex Meaney of Mean HVAC once said, “Air is squishy and hard to predict,” but there’s one thing about air that’s easy to predict.  If you turn on an exhaust fan inside the house, it pulls air from the house and sends it outdoors.  But that doesn’t mean the house has less air in it.

When a volume of air, a cubic foot for example, goes from inside to outside, a cubic foot will come in through the building enclosure to make up for that loss.  If this happens in one minute, we call it a cfm, which stands for a cubic foot per minute.  So in the building science world, we have this saying:

A cfm in equals a cfm out.

And that brings us range hood capacity.  How many cubic feet per minute does it move?

What size is your range hood?

First, let’s start by eliminating recirculating range hoods from this discussion.  In general, it’s best to have a range hood that exhausts to the outdoors.  Yes, Passive House designers like recirculating range hoods because they eliminate a penetration through the air barrier as well as eliminating the potential for negative pressure and the need for makeup air.  But let’s save that discussion for another time.

If you’re putting in a standard range or cooktop, whether electric or gas, you don’t need a hood with a huge exhaust rate.  Brett Singer, an indoor air quality researcher at Lawrence Berkeley National Lab, says 250 cfm should be enough.  Of course, that depends on hood design, location, and capture efficiency.  But just put the range against the wall and have a hood that covers the whole thing.  With that setup, a 250 cfm range hood should suffice.

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Going with a commercial range or cooktop?  That’s usually where we see people installing the super-duper range hoods with capacities of 1,000 cfm and higher.  If you’re dead set on having a range hood with a huge capacity, you may need makeup air.

Do you really need makeup air?

In my article on airtight homes and makeup air, I mentioned that we get a lot of requests for range hood makeup air systems in our residential HVAC design projects.  Then I wrote, “The first thing we try to do is convince them to put in a smaller hood so they don’t need makeup air.”

But when do you really need a makeup air system?  The HVAC Applications Handbook from ASHRAE (2019 edition) says this:

The exhaust rate of residential hoods is generally low enough and natural infiltration sufficient to avoid the need for replacement air systems.

That may be true for a lot of houses but not for many of the ones with big range hoods and an airtightness level that meets current building codes.  So what does the building say?  Here’s what the 2021 International Residential Code (IRC) says:

Where one or more gas, liquid or solid fuel-burning appliance that is neither direct-vent nor uses a mechanical draft venting system is located within a dwelling unit’s air barrier, each exhaust system capable of exhausting in excess of 400 cubic feet per minute (0.19 m3/s) shall be mechanically or passively provided with makeup air at a rate approximately equal to the exhaust air rate.

As you can see, it’s not simply a matter of range hood capacity.  You also have to have combustion equipment that’s not isolated from the indoor air.  Put a 2,000 cfm range hood in an all-electric home, and you won’t be required to install a range hood makeup air system.  That doesn’t mean you might not have problems; you just don’t have to put in makeup air.

Passive vs. active systems

Let’s say you decide you can’t give up that 1,200 cfm range hood, and you plan for a makeup air system.  You have to decide whether to go with a passive system or an active one.

Passive makeup air system.  With this type of system, you have a duct connecting the kitchen to the outdoors.  There’s nothing to move air from outdoors into the kitchen except the negative pressure created by the range hood.  You don’t want that duct to be open all the time, though, so it needs a damper that opens when the range hood comes on and closes when it goes off.

Deciding where and how to let that passive makeup air into the kitchen is where things get really tricky.  The best solution we’ve seen is this system designed by Ross Trethewey, PE from TE2 Engineering for NS Builders.  This isn’t a cheap or easy way to do makeup air, but it does seem to work.

Active makeup air system.  Rather than using negative pressure created by the range hood to move air, an active makeup air system has its own blower to move the air.  This is our go-to method for clients who hire us to do makeup air.  We use the Fantech makeup system because it includes a complete package and works well.

Fantech range hood makeup air system components

The diagram above shows the various components in the Fantech system.  It includes the wall cap, filter, damper, blower, silencer, and an optional heater.

Where to put the makeup air

Once you’ve decided on what type of system, you need to figure out where to introduce the makeup air.  Of course, the obvious location is the kitchen.  Somewhere near the range hood, right?  Here’s what the 2021 IRC says:

Kitchen exhaust makeup air shall be discharged into the same room in which the exhaust system is located or into rooms or duct systems that communicate through one or more permanent openings with the room in which such exhaust system is located.

So it doesn’t have to go into the kitchen.  You could put it in the great room, living room, or some other room that’s open to the kitchen.  Or dump it into the heating and cooling system so that it gets conditioned on its way in.  One advantage of putting at least some of the makeup air outside the kitchen is that the kitchen then will be under negative pressure.  That keeps kitchen pollutants from spreading out into the rest of the house.

Joe Lstiburek wrote a great article on this topic titled First Deal with the Manure and Then Don’t Suck.  In it he discussed a method that we try to use in our makeup air system designs.  Rather than putting all the makeup air into the kitchen, he puts about 60 percent of it into the kitchen.  Then he puts the other 40 percent into a heating and cooling system to be sent to rooms connected to the kitchen.

Other things to consider

This isn’t an All About Makeup Air article.  (Martin Holladay wrote that one at Green Building Advisor a few years ago.)  I’m giving you the basics here, but there’s still a lot more that goes into a good makeup air system design.  One of the big considerations, for example, is whether or not to condition the makeup air.  Having 5 °F (-15 °C) air blowing across your ankles isn’t so comfortable.  Nor is having hot, humid air fill your kitchen.

Similarly, it’s a really good idea to filter the makeup air to keep outdoor air pollutants from degrading your indoor air quality.  And of course, you need to plan for the best location of the makeup air intake.  You don’t want it right next to the range hood exhaust, for example.  Or the garage, dryer exhaust, or too near the ground.

Also, how will the makeup air system be activated?  There are products that allow you to do it with a direct electrical connection, pressure sensors, or heat sensors.  You’ve got to get this right because the makeup air needs to run simultaneously with the range hood.

So there you go.  Once you’ve digested all this, you should know enough to be dangerous.  Or at least what to look for in a makeup air system.  But the big thing I hope you take away from this is that you should just stick with a smaller range hood.


Allison A. Bailes III, PhD is a speaker, writer, building science consultant, and the founder of Energy Vanguard in Decatur, Georgia.  He has a doctorate in physics and is the author of a bestselling book on building science.  He also writes the Energy Vanguard Blog.  For more updates, you can subscribe to the Energy Vanguard newsletter and follow him on LinkedIn.


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This Post Has 11 Comments

  1. When I was doing energy audits we saw 2 houses that had commercial venting enclosures. One was an older home (maybe 1950s) that had an indoor BBQ grill; one was a much newer home that had one above a 6-burner gas range (looked like something out of a styling magazine). Both houses were greatly depressurized by the vent systems, so don’t think “old house, no problem”.

  2. Great article.

    Another factor to consider is that some (many?) range hoods don’t perform well against high static pressure – on either side of the blower. We’ve seen ‘400 CFM’ range hoods produce only 60 CFM of actual exhaust. Open a couple of windows and they jump up to 250 CFM. I presume the remaining missing CFM are gobbled up by duct on the exhaust side of the blower.

  3. Great article!!! Thank you!!! But I just have two gripes from my HVAC design experience:

    1) I would always avoid passive systems because, most often they will not make up the air of approximately what the hood exhausts (so we are infiltrating elsewhere), which violates the IRC codes (M1503.6 Makeup air required). If they flow hood the wall cap intake and exhaust in that posted video, the cfm difference between the two would be significant.

    2) Rarely would I ever, but in this circumstance, I must disagree with Dr. Joe Lstiburek, for I would not tie the residential kitchen makeup air into the HVAC system. These are intermittent or short-lived loads, and these hoods typically have 3 or 4 speeds, so activating the HVAC system for those monster range hoods on almost every use could be significant energy consumption. And by the way, one does not want the outside air cfm to exceed 25% of the furnace/air handler supply air, so be aware.

  4. I am soon to install a Fantech HRV which has some associated controls. During setup, exhaust and intake fans call for balancing. I expect any sort of range hood will unbalance the system and wonder if this is going to be a problem. Same holds for bath fans which you don’t mention though those are on the order of 100 – 150 cfm, at least the ones have installed. I plan to talk with Fantech so see if I might be able to access a mode with increased intake blower speed though expecting it to match a range hood fan would be a big stretch as my HRV is rated at 200 cfm max. I think any range hood we’d get would be 500 – 700 cfm. You mention 2000 cfm hoods which sound bodaceous! Good news is that I have a filter in the HRV input and it is very low pressure drop. Duct work is 6″ that splits into two 5″ diameter runs to opposite corners of the building with outlets on each floor so I should be able to move make up air through that OK. Absent doing anything special, seems like the HRV can only help and likely will flow better than rated under the influence of negative pressure albeit with its own in-house inlets maybe not doing much when the the range hood is on which could thwart the HRV function. Thoughts??

  5. Another timely, highly relevant, and well-written article by Allison! I would argue the number of houses needing intentional make-up air due to combustion equipment, house tightness, and/or exhaust fan size is much higher than most people appreciate. And as he mentioned there are several non-combustion related reasons for make-up air as well. Also a reminder that vented clothes dryers that can contribute to similar issues in our tighter homes, too.

    I’m a huge advocate for making our homes more airtight. However, with that comes an obligation to properly manage the mechanical airflows (flue gas venting, ventilation, exhaust fans, clothes dryers, etc.) and pay attention to the resultant house pressures.

  6. My favorite makeup air system in tight homes with moderatly sized range hoods is to bring air into the laundry room with a 6″ passive vent that incorporated a cape backdraft damper and then provide a pass through duct to the living space outside the laundry. This way I’ve got the dryer covered as well at the hood and I’ve got the hood exhaust depressurizing the kitchen relative to the rest of the home without adding very much expense. Just my two cents, but I’m of Scottish decent and we’re a thrifty clan.

  7. I am getting a 395 cfm hood and planning on opening a window if I turn it on, ESPECIALLY if I am burning wood in my zero clearance fireplace. Maybe that’s not right but now it’s in the past because I doubt my Mind could be changed. Thanks for the article!

  8. The FanTech balanced MUA system is the ideal solution for hods with multi-speed or variable speed blowers. There is a current sensor you install on the hood bower wiring that sends a variable voltage to the controller for the EC motor on the MUA system. With a little tuning you can dial it in to achieve just the right building pressure differential (under normal weather conditions anyway). We had a home with a Wolf 1200 CFM variable speed hood pulling so hard it would open the huge, heavy patio door 6 inches even though the original installer connected a 10 inch duct to the AC system return. With the FanTech system and a little tuning, we got the building to a 5 pascal positive pressure. In Houston you want your house to “Blow Out”, not “Suck In”

  9. Consider as well what large volume exhaust and make up air do to the heating and cooling load. Ten guests and lots of cooking will easily exceed the normal equipment sizing and cause comfort issues the guests won’t brag about. Make up air grilles, either fan or not, are best placed very close to the hood. In the floor at the range or the ceiling will “short-circuit” the impact on the remainder of the home.
    Plug 500 cfm exhaust/makeup air into your load calculation software and see how many “tons” to which it amounts.
    Don’t forget to heavily seal and insulate the intake air that might be zero degrees and cause condensation or 90+ degrees.

  10. This is a common misconception. If the exhaust device is delivering the desired airflow, then the same number of cfm will be coming from the outdoors — directly or indirectly. So the load is already there. The difference is that the load that might be diffuse or coming through the combustion vent, garage, crawlspace, sump. With intentional make-up air you know exactly where it is coming in and that air can be properly filtered and conditioned. And furthermore that opening can be sealed when it is not needed.

  11. I was pretty worried about make-up air for both my hood and dryer since my new house is so tight (about 1 ACH.) But I heard conflicting opinions since the house is 3800 sf with 9-10 foot ceilings and has a Zehnder installed. We temporarily installed the 500 cfm hood it in re-circ mode until we could get the make-up air system sorted out. I do wonder if we’d need it at all though. We certain detect no pressure changes when the dryer is running. I did just by a Manometer to take measurements.

    It’s too bad make-up air systems are so complex. You have to cobble together the parts yourself or pay a lot for one of the few very high cfm system.

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