Comments on: Range Hood Makeup Air: The Basics

By: Cindi

Cindi — Thu, 04 Jan 2024 20:46:27 +0000

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.

By: Patrick Huelman

Patrick Huelman — Fri, 06 Oct 2023 21:17:52 +0000

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.

By: Dean Sorg

Dean Sorg — Fri, 06 Oct 2023 19:34:28 +0000

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.

By: David J Small

David J Small — Fri, 06 Oct 2023 18:33:32 +0000

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”

By: Andrew Pisacano

Andrew Pisacano — Fri, 06 Oct 2023 02:55:00 +0000

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!

By: Michael Chandler

Michael Chandler — Thu, 05 Oct 2023 18:32:44 +0000

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.

By: Patrick Huelman

Patrick Huelman — Thu, 05 Oct 2023 17:00:01 +0000

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.

By: Dale Dellario

Dale Dellario — Thu, 05 Oct 2023 16:53:00 +0000

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??

By: Tony Amadio

Tony Amadio — Thu, 05 Oct 2023 16:39:43 +0000

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.

By: Walker

Walker — Thu, 05 Oct 2023 16:38:56 +0000

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.