GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Audio Play Icon Headphones Icon Plus Icon Minus Icon Check Icon Print Icon Picture icon Single Arrow Icon Double Arrow Icon Hamburger Icon TV Icon Close Icon Sorted Hamburger/Search Icon
Q&A Spotlight

Can a Range Hood and an ERV Get Along?

A reader asks whether installing an energy recovery ventilator in a new house will limit the capacity of a range hood

Should the capacity of a kitchen range hood be determined by whether a house has an energy-recovery ventilator? That is at the heart of a Q&A post by a GBA reader who's planning a new house. Photo: Kent Wang / CC BY-SA 2.0 / Flilckr

Roger is building a two-story, 3500-square-foot house that will have an energy-recovery ventilator (ERV) and a kitchen range hood. His question is about how this ventilation system will affect the range hood, and vice versa.

“Should one try to install a range hood exhaust with 400 cfm [cubic feet per minute] or less?” he asks in a recent Q&A post. “Would it be OK to install a 600 cfm unit in a home that has an ERV unit? If so, are there any special things to do differently when considering a makeup air strategy for a home that has an ERV with dedicated duct lines?”

An ERV supplies continuous fresh air throughout the house with its own ducts and it exhausts indoor air at the same rate, for balanced ventilation. Range hoods provide relatively powerful spot ventilation when needed, but do not replace that air; they are an exhaust-only appliance. The topic for this Q&A Spotlight is whether those two systems can work together to maintain not only fresh air, but also to balance pressurization of the house.

ERVs and makeup air?

Nicolas Bertrand wonders whether the ERV could be installed in such a way that it provided makeup air for the range hood. “Do they have a function where they could run as an inlet only for the house and have the exhausts blocked?” he asks. “This way the hood could do the exhaust work and the ERV supply some of the required air. I know a dedicated return-air supply is normally required for a tight house, and sometimes with an inline heater if it is cold outside, but maybe there is a way to rig the ERV to take its place.”

Probably not, replies Malcolm Taylor. He knows of no ERV that can run in an unbalanced mode to provide makeup air.  “For range hoods over 400 cfm,” Taylor says, “you need dedicated makeup air, either mechanical or passive.”

The simplest solution in Roger’s situation may be to pick a range hood that’s small enough so makeup air isn’t an issue.

Limit cooking options to match fan output

Roger’s research suggests that the range hood’s capacity should be linked to the Btu output of the stove in a ratio of 100 cfm per 10,000 Btu of heat. His plans call for a six-burner stove with a total output of 90,000 Btu.

He could stay with a 400 cfm range hood and limit the burners used at the same time to no more than 40,000 Btu. Or he could up the capacity of the range hood to 600 or more cfm to allow multiple burners to run at the same time. That would mean introducing makeup air.

“The concern, reason to pause, is if option B is chosen, does a makeup air system need to be done differently because a home has an ERV present?” he asks. “Also, if multiple burners are on at a medium temp, could one get away with a 400 cfm vent hood and eliminate the headache and cost of incorporation a makeup system into the home.”

Better not to limit the use of the stove, Taylor suggests. Just get the range hood you need to provide good ventilation, and if that means you need makeup air then install a dedicated vent in the kitchen or just crack a window. The 400 cfm cutoff, by the way, is a code provision, not whimsy, Taylor adds.

“The assumption with bathroom exhausts, dryers, and range hoods under a certain cfm is that they don’t unduly depressurize a house,” he adds. “Tight houses will have a certain amount of of air leakage and pressure differences caused [by] wind and the stack effect. Unless you get to Passive House levels of air tightness, these appliances shouldn’t cause problems.”

ERVs supply balanced ventilation, Taylor says, so no matter how they are operated they still aren’t designed to supply makeup air.

One homeowner’s solution to the problem

Bertrand is facing a similar situation. He’s also building a new house, and his wife, a “serious cook,” is insisting on a range hood. “End of story,” he says. “I can’t argue with her because I don’t like smoke or grease fumes in the house and she cooks like no other!”

Bertrand has settled on a variable-speed range hood with a maximum capacity of between 600 and 800 cfm. He envisions a makeup air system with dampers and possibly an inline heater for colder months.

“It’s not great for a super airtight house that is trying to conserve energy,” he adds, “but it’s not like she cooks 8 hours a day or anything. At most it would get used a couple hours a week I’m guessing.”

His biggest qualm is that the dampers in makeup air systems seem a “little flimsy.” He’d rather have a product with a more robust damper that seals tight and is well insulated.

Combustion appliances can be a problem

Depressurizing a house is a problem when combustion appliances are used (back-drafting can bring carbon monoxide into the house), Akos says. But a house of 3500 square feet would have to be very well sealed in order to have pressure issues with a 600 cfm range hood.

In a house with air leakage of 3ACH50 (standard construction), Akos writes, a clothes dryer, a 600 cfm range hood and three bathroom fans of 50 cfm each would not be enough to significantly unbalance the ERV.

“I think overall, for a large electric-only house, this doesn’t feel like a big issue,” he adds. “Range hood[s] don’t run for that long, plus you can always crack a window if you need to run all these exhaust fans together at the same time. I guess you can put in a [makeup air system] but I wouldn’t do much more than a well sealed barometric damper.”

Houses with open-combustion appliances are, of course, a different story. In that case, even a pressure difference of 5 pascal could be a problem.

Tight houses starve fans

One thing that will happen in a tight house, says T Carlson, is that fans won’t work at full capacity.

“Unless you provide makeup air your actual fan exhaust output will be much less, so you either up size the fan and it starves down to what you need or give it makeup air,” he says.

In his own house (air tightness at 0.55-0.60ACH50), T Carlson said he tested 80 cfm Panasonic bath fans at about 40 cfm; 110 cfm Deltas with humidity sensors were actually running at about 80 cfm.

He has a 350 cfm hood over a gas cooktop, which puts some “serious depressurization” on the house even with a 6-inch, gravity dampened makeup air intake in the basement.

“In my opinion you should oversize fans and let them work harder to get you what you need,” he says. “Provide makeup air to the house from the laundry room to give the dryer a little extra to work with. You shouldn’t have problems. That’s what my house has been doing for just over 3 years.”

Our expert’s opinion

Peter Yost, GBA’s technical director, adds this:

There is quite a bit of active research and resources on the issue of ventilation in tight houses, makeup air for exhaust fans—particularly kitchen range hoods—and the efficacy of range hoods.

Most of the resources I include below came my way through Laura Capps at Efficiency Vermont. An excellent researcher and engineer, Laura did a presentation for our local building professionals group on the relatively new Efficiency Vermont Healthy Homes program.

Here’s one source of information: “Reducing Appliance Backdrafting Risks With HVAC-Integrated Makeup Air Systems” (Mike Turns, Pennsylvania Housing Research Center, Cityscape: A Journal of Policy Development and Research • Volume 15, Number 1 • 2013).

An illustration from his work shown below deals with house pressures, exhaust rates, and airtightness. From the report: “Even modest levels of exhaust can create risks in tight houses that contain combustion appliances. Similarly, very high exhaust rates may create risks even in relatively leaky houses.”

But what’s really striking in this report is Turns’ discussion of the two main types of makeup air systems—engineered openings and HVAC-integrated. Turns wrote: 

“Although appealing in their simplicity, engineered openings are effective only at relatively low pressures, and thus relatively low kitchen exhaust rates. With exhaust rates of about 150 cfm or greater and a 10-square-inch opening, the pressure required to let in a roughly equivalent amount of air is already greater than the pressure that could backdraft a masonry fireplace. In addition, there is no opportunity to heat or cool the incoming air, which can lead to occupant discomfort.”

Regarding HVAC-integrated makeup air systems (see the second illustration from his report below), Turns wrote: “HVAC-integrated makeup air systems allow for much higher rates of air intake and provide the ability to temper incoming air via the HVAC unit (when it is operating) or via a standalone duct heater or dehumidifier.”

Other sources of information include:

  • Ducted Range Hoods: Recommendations for New and Existing Homes” (Thomas Phillips, December 2019, The ROCIS Initiative (Reducing Outdoor Contaminants in Indoor Spaces). This report is packed with solid tips and tools for operating cooktops and exhaust systems, how to install systems properly, and cautions and caveats.
  • Lawrence Berkeley National Laboratory Indoor Environment Scientists Brett Singer and Iain Walker have been doing a ton of research and work on evaluating range hood efficiency, including the development of a new standard, Test Method for Measuring Capture Efficiency of Domestic Range Hoods (ASTM WK55797 as reported in ASTM News, “Proposed Standard Will Test Range Hood Ventilation.”

This is a really tough issue. I am working with a client in a relatively new home—around 1ACH50 airtightness, a wood stove with dedicated combustion air, a four-burner propane cooktop, a 400 cfm kitchen range hood, and a Minotair Pentacare for balanced mechanical ventilation. When the range hood is on, I measured -19 pascal pressure in the home. We can’t use HVAC-integrated makeup air because there is no central forced-air system, and Turns’ article suggests that it just is not possible to do an interlock makeup air duct system. We are at the point of requiring the client to eliminate their propane cooktop, their woodstove, or both (and not to mention difficulties they are having with their clothes dryer).

Maybe we will end up with residential versions of this commercial mechanical ventilation system: enVerid HVAC Load Reduction (HLR) borrowed from systems developed for submarines!


Q&A Spotlight it compiled by Scott Gibson, a contributing writer at Green Building Advisor and Fine Homebuilding magazine.

19 Comments

  1. Randy Williams | | #1

    Not sure how old the table is in exhibit 1 but 1,000 [email protected] is a high leakage rate for most new homes being built in my area. (Majority are under 2500 square feet and closer to 700 [email protected]) I try to steer my customers away from woodstoves and gas ranges. Make-up air is a problem in my climate, around 100 hours per year with temps below -20°F. Last heated make-up air system I worked with required a dedicated 100 amp electric service to handle the heating of the make-up air. Homeowner decided to go with an unheated system. Haven't heard how that's working out.

  2. Trevor Lambert | | #2

    Visa-versa? Vice versa.

    1. User avater GBA Editor
      Brian Pontolilo | | #3

      Vice versa, for sure, and that was my mistake. I intended to circle back and check it when I was working through this, but never did. Fixed now. Thanks...

  3. John Rockwell | | #4

    Hi Everyone. I'm glad this is being addressed, if only to provide a definitive answer "no" to the oft-asked question "can the ERV provide adequate make up air for my range hood."

    ERVs are sized to provide acceptable indoor air quality. The continuous mechanical ventilation rate of most homes is substantially below the flow most range hoods. Ignoring temporarily the hotly debated controversy about ASHRAE 62.2 infiltration credits, the worst-case scenario for a 2,000sf, 3-bedroom house is:

    (2,000cfm)(.03cfm/sf) + (7.5cfm)(BR + 1) = 90cfm.

    In Nicholas Bertrand's cook's kitchen, even the low end of the range exhaust (600cfm) is nearly SEVEN times the ERV flow rate. Simply put, the fans in an ERV sized for 90cfm will never be able to provide that much air. And if they could, the duct system would have to be sized accordingly, and only for the times when the range hood is in use. Thus the ducts would be grossly oversized for the majority of the time.

    So, even if one installs a range hood rated for less than 400cfm (to avoid the requirement for makeup air) there will either be some serious depressurization or all the various penetrations in the home INCLUDING the ERV will allow infiltration when the hood is activated.

    In a home I designed recently, the blower door test resulted in 0.4 ACH50 (191cfm). Of course the ERV exterior grilles were taped off. I chose a 350cfm range hood (to avoid the hassle of makeup air and the energy penalty of tempering it). It stands to reason that when the hood is activated, every possible penetration will contribute some make-up air...INCLUDING the ducts for ERV intake and exhaust. And guess what? Nobody has died, nobody notices any comfort issues, and there was no noticeable increase in the electric bill.

    John Rockwell
    Zehnder America

  4. yolotom | | #5

    Scott:
    thanks for mentioning our best practice guidance document for ROCIS.org.

    For a quick overview, your readers may also be interested in the 2018 NAPHN conference presentation at Downloadable PDFs at http://rocis.org/kitchen-range-hoods. It addresses make up air, low E airtight homes, electric stoves, and recent research on ERVs and cooking emissions.

    Tom Phillips

  5. Steve Hoge | | #6

    Rather than a separate heating unit for external makeup air during winter-time operation, it seems like you might be able to use the outer insulating jacket of an appropriately-sized double-walled exhaust duct to heat-exchange the incoming makeup air supply with the outgoing exhaust air from the range hood.

    1. Andy S | | #17

      I was trying to figure out if this exact setup would work for a current build but couldn't get around the damper aspect. Those double walled pipes are used for closed systems like gas fireplaces where you're not worried about having to close them off to stop cold air from coming in when the fireplace isn't running. In that setup the cold air just blows through the firebox and back outside. For a range hood it'd be dumping cold air into the house all the time unless you could damper both the intake and exhaust.

  6. Calum Wilde | | #7

    For the dryer issue, a ventless heat pump dryer could be an option. But the obvious time penalty exists if moving from propane.

  7. user-7025742 | | #8

    Afternoon all. I've been attempting to obtain a definitive answer to this exact question since 1993 when I had a 2200 sq ft bungalow built in southern Ontario near Trenton. The house was an R2000 build with 2x6 wall studs,6"wall insulation and about 12" of blown cellulose in the ceilling. The air transfer was tested when the construction was complete and the Independant tester advised that my home was the second tightest home he'd tested. The heating system was and is Hydronic Forced Air with a High Performance NG water heater (Polaris 95+% efficiency) intake and exhaust to the exterior of the structure. The house has a NG Clothes Dryer which uses inside air and vents out, NG fireplace that draws air from outside and also exhausts to the exterior of the house. I have replaced the HRV a few years ago which runs through the winter 20 minutes plus when ever the furnace kicks in. I have had an unducted range hood for years and we are in the middle of a Kitchen Reno and are about to purchase a range hood and complete said reno. What kind of power do I need? by you article I'd say about 800 Cuft exhaust, and makeup air. One suggestion was to dump makeup air over the stove, however midwinter I fear everyone would feel the cold that would accumilate 2 to 3 feet off the floor of the kitchen/familyroom. It would likely drive anyone out of the room within minutes. Adding another electrical element to heat the incomming cold air would likely be expensive to operate. ( Just paid $199 equal payment to this months electric bill.) I don't know what to do.
    Signed, Scratching my head in Ontario (the hair is just about gone on top and I'm working on the sides)

    1. Matt V | | #12

      The "greenest" option would be to get an induction stove and use a smaller range hood. But if you already have a stove that might not be a good option.

      Otherwise I think there is no good answer. What we need is a HRV specifically designed and listed to be used with a range hood. Compared to a regular HRV, it would need to offer higher flow rates (800 CFM or more), and it would need to be able to handle some grease. I don't think anything like that exists right now.

  8. user-7025742 | | #9

    PS: Got an engineer wound up when I told him that I was going to directly pipe the range hood into the HRV collection pipe in the kitchen. It was an interesting conversation as I made like I didn't understand his consern

  9. differentpath | | #10

    I investigated several of the above suggested alternatives and found them both overly complicated and expensive. In my 1750 sq ft sip panel house with ERV(200cfm max) and 600 cfm max range hood I did the following with excellent results over the last 3+ years.

    Induction cook top
    600 cfm range hood with baffle type grease trap
    NO make up air
    No make up air heater (we live in heating dominated climate)
    No range hood exhaust roof penetration

    The way my system works is the hood traps grease particles then vents the exhaust into adjacent mechanical room through a large activated charcoal filter box to capture odors. There is an 8” dia. ERV exhaust duct above.
    When I cook (I do a lot of aisian cooking IE: stir frying ) I ramp up the ERV and use the range hood at a flow rate that will capture vapors. I do not have odor, vapor or negative pressure problems. This approach requires a high quality grease baffle hood run at conservative flow rates and a cheap fabricated filter box and that is it. I clean my ERV filters(MIRV 13) about every 8 weeks and have not observed any grease buildup in the media whatsoever. The system is Inexpensive and effective.
    I find the building science data very interesting and useful but the proposed solutions in this case have many down side that are not addressed like complexity, expense, reduced air tightness and energy efficiency. I welcome any comments or questions, Cheers

    1. Deleted | | #11

      “[Deleted]”

    2. Malcolm Taylor | | #14

      That's an interesting solution. I wonder if conceptually it's any different than having a filter on the HRV return, and either having that return over the range, or directly ducting the hood into the return? In all three cases the system relies on the filter to keep the HRV clean.

      A second question would be: Isn't it really just the efficiency of the filter you made that distinguishes any of those solutions from just using a recirculating range hood?

  10. user-6892763 | | #13

    I appreciate the various concerns stated and agree that an ERV is not the path for hood make-up air. I also agree about not using a hood larger than what is really needed.
    I think Mike Turns' info about a 10 sq. in. engineered opening not being enough is somewhat misleading. Doing the math, that's less than a 4" diameter intake (2^2 x Pi = 12.6 sq. in.).
    I like the simplicity of a motorized damper that is wired to the hood fan switch and introduces the make-up air at or near the cook surface. If the intake, motorized damper is an 8" round duct (4^2 x Pi = 50.3 sq. in.), my guess is the extreme negative pressure danger isn't going to happen with a reasonably sized hood.
    I live in the south and so acknowledge that our houses aren't super tight and people rarely freeze to death; I think the engineered opening is viable for us and probably is my preferred approach.
    Best, -mike barcik (special greetings to Mike, Peter and Laura!)

  11. differentpath | | #15

    Regarding Malcolm Taylor’s comment: Yes I agree it is conceptually the same but functionally different in that the exhaust through the activated charcoal filter is only in the same room as the ERV exhaust and not piped into the system so the opportunity exists for plenty of mixing with ambient air to occur before it is evacuated. I should also not that the activated charcoal filter is large 24” X 24” so more area than could be inserted into a pipe run. Please note the filtration is two stage, first the vaporized oil is removed and then the odors. It is basically a modified recirculating range hood strategy so no pressure imbalances and no damage to the ERV filter media and in my case less expensive than any of the other suggested solutions.

    1. Malcolm Taylor | | #16

      One thing that still strikes me though is that unbalance between the CFM of the range-hood and the HRV return. For short periods of use it probably performs as y0u have described. But if the range-hood is on for a while it is pressurizing the mechanical room, so the air in it isn't really ambient air, but rather is entirely supplied by the fan, and the majority of the filtered air in the mechanical room must circulate back into the house. If that is so, I wonder if it makes much difference where the mixing occurs? If you could fit a filter into the cabinet above the range-hood, maybe it would be possible to do all the same things within the kitchen.

  12. differentpath | | #18

    Malcolm,
    Hmm, you are maki g me think about this but here goes:
    There is no pressure imbalance created by this re-circulation strategy. The overall building envelope is pressure balanced by the ERV. The range hood is taking a portion of that air and moving it from one area to another (the spaces are adjacent and communicating as in no separating door so no opportunity to over pressurize the mechanical room which is quire large and should actually be called the mechanical/laundry/storage room. The air in the mechanical room does not recirculate back into the house because it has a oversized(8”) ERV exhaust duct. You could fit a filter into a cabinet above the range hood as you suggested but then you might as well just get a manufactured recirculating fan. The downsides are the units I looked at had very limited filtration capacity except for one with very expensive activated carbon canisters. I think the important considerations if you go that route is make sure you have oil vapor baffling in the hood (like restraint fans use) and an ER V exhaust in the same room as the fan discharge.
    By the way we cook and bake A LOT and do not have any odor or excess humidity problems in an very tight air sealed house.

    1. Malcolm Taylor | | #19

      I don't want to nit-pick at what is an interesting and obviously effective solution (and by the way - nice kitchen!), but I still think your system works because of the quality of the filtration you have made. An average ERV, whatever the size of the exhaust duct, moves somewhere in the range of 100 - 200 CFM of air. Your hood is exhausting 650 CFM, so the balance must be recirculating out of your mechanical room into the rest of the house.

      Probably the biggest impediment to others copying your set-up is that the overwhelming majority of homeowners simply don't do any routine maintenance. If they can't regularly replace the filters on their furnace, ERV, water-purification, etc., what are the chances they will keep that range hood filter clean? You belong to that rarified group of people who maintain things. Hardly anyone I know does.

Log in or create an account to post a comment.

Related

Community

Recent Questions and Replies

  • |
  • |
  • |
  • |