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Tying Cooktop Exhaust into HRV System

DrDanger | Posted in General Questions on

I am building a new home to PassivHaus standards, while undergoing LEED certification. The LEED section on ventilation pertaining to kitchens seems unclear to me. We are providing ventilation of the kitchen via an HRV, but we couldn’t possibly tie in the ventilation unit that comes with the cook top (downdraft) as it uses a 600cfm motor. We instead were going to tie in the downdraft to a filtered recirculation unit. Our HRV installer said that he has heard of people tying in their cook top ventilation to their HRVs, however I am concerned that this would invalidate the warranty and greatly shorten the lifespan of the unit.

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  1. GBA Editor
    Martin Holladay | | #1

    Large kitchen exhaust fans -- whether range hood fans or downdraft units -- are incompatible with tight, energy-efficient homes. If you insist on using a 600-cfm downdraft exhaust fan, you will need to provide a makeup air unit; and if your makeup air needs to be conditioned (heated and cooled), the cost quickly becomes astronomical. Even of you use unconditioned makeup air, there is a substantial energy penalty.

    I suggest you install a range hood with a small exhaust fan (150 or 200 cfm) and use the fan as little as possible. Many Passivhaus builders go with recirculating range hood fans to avoid the problems you are encountering.

    Don't ever hook up a range hood fan or a down-draft fan to an HRV or an ERV.

    1. alexdorf | | #35

      Has there been any new tech on this? I thought I caught a video of a guy where Mitsubishi had provided a unit to offset the range hood.

  2. homedesign | | #2

    do NOT tie cooktop ventilation into an HRV
    There can be an independent exhaust port elsewhere in the kitchen that ties to an HRV

    minus 600 LEED points for using a 600cfm recirculated downdraft ;-)

  3. Andrew Henry | | #3

    I question how necessary a kitchen range hood is? If the house has a ventilation system (preferrably an HRV) you can exhaust air from the kitchen provided the exhaust intake is a suitable distance away from the range. The air turnover from the HRV at high speed will do an adequate job of removing odours. It may take longer to remove the odour than a range hood but it will remove them.

    If the odours created when preparing food are unappealing then I can't imagine the food tastes all that good. Consider preparing something that smells better when it's cooked. I don't have a problem with my kitchen and eating area smelling like the curries I occasionally cook, smells good to me. And I know the HRV is removing the odour as guests who have come over for dinner remark that when they walk to the door they can smell the curry.

    The HRV will be doing the job of removing the humidity thrown off while cooking to. So, other then having odour and humidity removed immediately is a range hood really necessary? It just seems like kitchen bling in the same way a stainless steel commercial range is.

  4. Derek_Vander_Hoop | | #4

    While at the Passive House conference this past October, we had the opportunity to tour four homes, one of which was a beautiful custom home out in the country outside Champaign/Urbana. I've often wondered how I would handle a downdraft like the Jenn Aire we currently own in a Passive House. The last home we toured had a downdraft and it was handled by a filter under the cooktop as you see here, ultimately vented out through the toekick. I thought it was a perfect solution.

  5. DrDanger | | #5

    Thanks for all the responses! We are definiely planning on a recirculation unit for the downdraft of the cook top, which should be nearly identical to the last post. If you look closely at the picture you'll see 2 long black strips. These are replaceable charcoal filters. We are going to have a HRV return from the kitchen area as well. Now I just wonder if that will keep the folks at LEED happy.

  6. Riversong | | #6

    Is this an electric or gas range? If gas, then combustion products need to be vented to the exterior. CO levels are typically high near a gas cooktop, and gas combustion produces water vapor in addition to the moisture from the food. In either case, spot ventilation to the exterior during cooking is important for removal of moisture (not cooking odors). ASHRAE 62.2 requires 100 cfm on demand or 5 ACH continuos for kitchen ventilation.

    600 cfm is not only unnecessary, it's counterproductive to electrical conservation and heat conservation. Recirculating that volume and velocity of air will not eliminate moisture and will cause drafts that decrease occupant comfort.

    There is no place in a tight, efficient home for such a monster. In a PassiveHaus, it borders on insanity.

  7. DrDanger | | #7

    Thanks for the response Robert
    The cook top is an electric induction type, however the downdraft made for it only comes with a 600cfm motor. Having had a similiar set up in anther house, I only plan to use it very infrequently. It does seem that I'll need to talk with the HRV subcontractor to make sure that we can get 100cfm on demand. We are having a HRV return vent in the kitchen so the other option you mentioned, 5 ACH continuous would also work.

  8. gary davis | | #8

    I think Derek has an effecient concept,I am going to use the idea ,however I think I will charcoal filter the air intake and exhuast which will exit at the top of the cabinets in order to recirculate the heat that will naturally be rising to the kitchen sealing . I am about to start my kitchen design and this was a problem as I wanted to remove the wall the stove was on but we couldn't figure out what to do with the range hood,problem solved.Like Andrew I also wonder just how important of a function the hood fan serves ,, you ,in commercial applications I can see it where you have massive amounts of food being prepared constantly , you need to turn the air over and remove the moisture and hey that is the resturants best advertising floating through the air makes you want to go in and eat.

  9. ChrisBriley | | #9

    I'm working on a house with an island cook top. There is a strong desire to not have a hood (mostly for aesthetic reasons). LEED wants the kitchen exhaust vented directly to the exterior. And there is evidence that grease laden air is carcinogens. So our solution ‘Du Jour ‘ is to use a GE Profile telescoping downdraft fan (similar to the Seimens). Our thinking is that it will be used rarely (frying burgers and fish will be a rarity.) And on those days when humidity is an issue it might be used (boiling lots of Pasta?), but otherwise… not so much. It’s there “just in case”. The most attractive feature is that the fan is variable so you don’t have to blast 500cfm every time. I’m not sure how low it can go yet, or how loud it is. There’s nothing worse than having to shout at your dinner guests over a fan. I think this keeps LEED happy, clients happy, and me happy by not tying it into the HRV. If it runs at 500cfm it should just throw the HRV out of balance but shouldn’t depressurize things enough to create a problem. Or so the thinking goes. Am I crazy?

  10. homedesign | | #10

    Cooktops on Islands have never made sense to me.... you say it may not be used very often ....then WHY locate it on the island?
    The current client may prefer the microwave or make "reservations" for dinner. ;-)
    What about the next owner?
    Cooktops should be placed near a wall and an exterior wall is preferable.

  11. Riversong | | #11

    I'm with you there, John B. And that was a nice way of answering CHRISBRILEY's question "Am I crazy?"

    Not only is it foolish to locate a cookstove on an island counter, but it's even more foolish to incorporate a 500-600 cfm fan in a very tight house. May as well open the windows in winter when there's a gale blowing.

  12. Christopher Briley | | #12

    Thanks John and Robert. (And I do appreciate the imoticons to convey the good natured tone of the writings, it can be hard for the right tone to come across) . The fan on the island is the thing that will be used rarely. THe coocktop will be used often, the fan probably only when someone burns something or is generating mass amounts of grease/steam/smoke (i.e. rarely). The only reason an exhaust fan is being considered if because of LEED and the rare occasion mentioned above.

    I was about to argue that an island can be a great place for a cook top, and then wondered if you guys had said this because there is a GREEN reason not to locate the cooktop on the island. (other than poximity to imediate exterior air for venting) Or is this a personal design preference? Just curious.

  13. homedesign | | #13

    It is my understanding that Venthoods perform better than downdrafts and that Venthoods against a wall perform better than "Island" Venthoods.
    I have had clients tell me of bad experiences with downdrafts(poor performance)
    I suppose if you use a strong enough fan .... a downdraft might work (and use more energy).

    Many of my clients make reservations for Dinner is sort of a Dallas "joke"
    When the mom says it's time for dinner.... the Kids head for the car....;-)

  14. Kevin O'Meara | | #14

    Thanks everyone for your contributions and ideas! Now looks like a good time to recap my situation. Several people have expressed concerns over placement of a cook top in an island. I am uncertain as to why other than a wall mount overhead hood is more effienct at drawing up the smoke, etc. In our home we are very fortunate to enjoy some incredible views out our South facing windows, this and our habit of actually cooking at home, helped guide the design. Our kitchen tends to be a place where we spend most of our time. We spend time there while preparing (and eating) appetizers and the meal. Since we spend so much time there we designed the kitchen so the cook doesn't get put in the "penalty box" when preparing meals.
    Then the next decision was on venting...but again aesthetics are important. The last thing We wante was obstruct our views, and also when standing they tend to block eye contact with the other people across from it. So we looked at downdraft units. I agree that are not the most efficienct way to draw smoke/odors but the newer ones that raise up a bit higher (13" on our model) does help overcome this a bit.
    Since this house is built to passive house standards I was also opposed to an overhead hood and venting outside for 2 reasons. First it punches a rather large hole in my thermal envelope, secondly, is the loss of BTU's when it is directly vented outside. The folks in Germany that build their passive houses very commonly avoid these two problems by using a recirculating vent hood. One in particular, Berbel, uses centrifuge technology and filters that works very well. I even found a person who had talked to Berbel to become a US distributer, but the cost was prohibitive....about $5000.
    Having had a cooktop with a downdraft, like other people who commented, I found that I didn't need to use it much. So I anticiapate the same in the future. This helps mitigate against the nergy costs of running a 500 CFM motor. The down draft unit has two stages of filtration. The first is in the downdraft unit itself, and is a grease trapping filter, which can be washed in our dishwasher when needed. The second are 2 carbon filters that help reduce the smoke and odors and have to be replaced periodically.
    The last part was to folow the ASHRAE 62.2 requirements and have an air return to the HRV from the kitchen area that was compliant, which we were able to do, and now remain LEED compliant without compromising passive house design. We also were able to satisfy our own unique lifestyle and aesthetic senses without incurring significant energy penalties. Thank you very much for all your contributions. Kevin O'Meara

  15. user-626934 | | #15

    Island cooktop (electric induction). I cook on it three times a day. The island is beautiful and the kitchen is really fun and functional to work in.

  16. andrei | | #16

    We are building in the spirit of passive haus but seeking LEED, and were frustrated to find out that a recirculating hood is NOT permitted by ashrae 62.2, the reasoning being that the feature must be maintenance free. A recirculating hood has a filter that inevitably does not get changed/cleaned when it should. If I am understanding, a downdraft involves a filter and includes no venting or penetration to the outside. So how can it be compliant with Ashrae 62.2? We are finishing our kitchen design now and would love to know!

  17. GBA Editor
    Martin Holladay | | #17

    Most downdraft fans are vented to the exterior, but some Passivhaus builders connect them to filters and exhaust them to a home's interior.

    Both LEED for Homes and the Passivhaus standard are voluntary programs. Choose your program, and comply — or don't — as you wish. No one said that either standard is consistent with other programs — or even logical.

  18. Riversong | | #18


    ASHRAE 62.2 does not require that mechanical ventilation equipment be maintenance-free (no mechanical equipment is). It requires spot ventilation in bathrooms and over the kitchen range to evacuate humidity and odors to the outdoors.

    That is an eminently sensible requirement. PassivHaus's obsession with restricting air exchange is not sensible or necessary for efficient and healthy living.

  19. pderas | | #19

    Well. I guess I'm the first kitchen designer to comment here...

    1. Far more time is spent at the sink than the cooktop in both prep time and cleanup. Better to put the main sink on the island and the cooktop against the wall where it can be efficiently vented to the exterior. Conditioned makeup air can be supplied, when needed, to compensate for the ventilation (Is it really true that LEED would not permit this sensible solution???).

    2. Downdraft venting is (at best) only 25% effective compared to a hood with a canopy large enough to capture steam and grease and gas vapors until the fan can pull or push them to the exterior (subtract the gas vapors for electric and induction).

    3. Seems as though nobody here in LEEDland really cooks. Sauteing, frying and stir-frying generate a great deal of grease-laden steam. 75% of that is going to be deposited on your ceiling, walls, cabinetry, etc. with a downdraft.

    4. Recirculating the air from cooking activities really makes ventilation an exercise in futility.

    5. As much as I decry the habit and work to change it, consumers still want monster ranges and cooktops. The manufacturers of same REQUIRE massive venting of these cooking appliances and building department officials defer to the manufacturers' installation instructions. Ideally all consumers would spring for an induction cooktop. In reality, that's not going to happen.

    Bottom line: Only those cooks who confine their efforts to boiling water, the oven and microwave are not going to need proper ventilation (even boiling water becomes a problem in a humid climate).

  20. Dennis | | #20

    I am working on a similar project: A very tight and energy efficient home, downdraft kitchen hood. We are certifying project to LEED for Homes. Approach is simple:

    - Recirculating down-flow hood with filtration system. We recommended an up-flow hood, but owner insisted on the down-flow design.

    - An HRV dedicated to the kitchen, and sized per ASHRAE 62.2 requirements for kitchen exhaust (requires 5 kitchen ACH, 100 cfm minimum intermittent).

    - The HRV is interlocked to run when hood fan in on (or if a separate wall timer switch is activated).

    - General whole house 62.2 ventilation is provided by other HRV units.

    - An induction cooktop is being used (but is not required).

    I think the homeowner will be happy with the results. In any case, he is fully aware of the design considerations. I think this meets all code and ASHRAE 62.2 requirements.

    I am aware of a passive house that was designed with no kitchen hood at all, only an ERV general exhaust from kitchen. I think this is a mistake, and a code violation, but it will likely work OK anyway.

    I have lived in several homes with cheap range hoods that were not vented to outdoors. We never even bothered turning the hood fans on, as all they seemed to do was make a lot of noise. Of course these homes had lots of infiltration to eventually get rid of odors. A general ERV/HRV ventilation system would likely do an even better job at that.

  21. Expert Member
    ARMANDO COBO | | #21

    Sorry for coming late to this discussion, but it maybe good for some to know of a
    NEW CODE in 2009 IRC: "Code M1503.4 Makeup Air Required: Exhaust hood systems capable of exhausting in excess of 400 cfm shall be provided with makeup air at a rate approximately equal to the exhaust air rate. Such makeup air systems shall be equipped with a means of closure and shall be automatically controlled to start and operate simultaneously with the exhaust system". So, if your State/Local code is 2009 IRC, you must comply.
    I agree w/ Peggy, several “high end” manufacturers do require specific hoods and, as far as I have researched, none have a hood with makeup air built-in. Some of this hoods are 1200 cfm; and without getting on the discussion “if this is a green house”, if a client wants “that” appliance they must PAY to have a good makeup air designed and built-in.
    For now, I've started to specify this in every home I design and I'm thinking about this system,, it can be installed in a pantry, attic, etc, and it can be supplied near the stove/hood (above the stove, by the side's on the wall or below by the base cabinet's toe kick) so there is minimal air exchange from the rest of the house. If anyone has a good/better idea I would love to hear it.

  22. Stacy Yeomans | | #22

    Our house is 2 years old. We have never had problems before, but in the last 2 months our cabinets under the cooktop and down draft have collected ALOT of moisture and mildew. It is so much, I now have to leave the doors open all the time. My contractor does not know why. Does anybody have any help or suggestions. We spend a ton on our cabinents and I dont want them rotting away! THANKS so much!

  23. Armando | | #23

    my best guess is that the down draft is dumping directly to your crawlspace and is not dusted to an exterior vent. Duct and vent the exhaust to an exterior vent.

  24. Chris | | #24

    We have an adjustable vent in our basement that we use to let the heater get more make up air. We keep it clean and its probably going to get an electric damper soon so that it can be told to open wide open (and maybe be supplemented by a fan) whenever the kitchen or bathroom exhaust fans are going. We also have an HRV which is on pretty much all the time (at various speeds..and duty cycles)

    We could not do without fans of one kind or another because cooking generates a lot of water vapor.

    What I would really like to see is a digital panel on the HRV that would provide several presets that unbalanced the fan to provide makeup air (increase air intake, not air exhaust) Then those presets could be utilized, say low or medium when kitchen or bathroom fan was on, and high- an adjustable high setting for both. That seems like the most common sense solution. That way, unless the exhaust fans are on for a very long time and are very powerful, the makeup air will be warmed to a variable extent by the nonkitchen exhaust air. (Its desirable to have a return damper for your HRV in your bathroom but kitchen fumes would probably screw up your ducts - leading to a MAJOR pain in the butt to clean.them)

    Maybe in the future, for mild climates, we'll start seeing fans come in pairs.. and for the rest of us, dedicated kitchen-ready HRVs- completely designed for cleanability, (mold-sensitized people, also need this feature).

    If an HRV was designed with super easy and frequent - and utterly thorough - cleaning in mind- which especially requires that the ducts to the outside be accessible from the inside for cleaning- fully accessible, ideally, the entire assembly, including the motor area- should be easy to disassemble, wash, or at least wipe down thoroughly, and reassemble - it would be fine as kitchen ventilation.

  25. Chris | | #25

    Whoa, I forgot something really important.

    The stack effect - a major player in this situation.

    All you folk here who know this inside out, I hope you will forgive me for bringing this up. Its boring, but its super important. Obviously, any chimney is a stack.. a smokestack.. So is a home or any building.

    Kitchen exhaust air is warm. So, especially in the winter, make up air should come in to the house as low on its side as possible. Ideally, into the basement.

    Another thing- opening any upstairs window WON'T help you defeat backdrafting in the winter. It will make it worse!

    If its windy, opening a window on the downwind side of your house can do the same thing.

    The best solution for high CFM backdrafting might be a very simple one, a 117 volt coil relay that is connected to the fan motor that is used to control an low voltage electric damper on a large vent that penetrates the wall of a home at the basement level, allowing a substantial amount of cold, fresh outdoor air in, low on the side of the building, in an unoccupied part of the home. I don't know if adjustable electric dampers exist but that would be even better. Or, add a fan to the vent to enable various levels of make up air.

    Open the vent for one fan, still more for two. Or open the vent for one fan, turn on a fan blowing in to supplement the vent for two.

    For a 1200 CFM fan, you might need a very large vent and fan.

  26. Anonymous | | #26

    By the sounds of it, code will eventually require the same fan that sucks the air out to suck 'make-up' air in, at the same rate.

    It would make sense anyway, since the ventilated air from the stove ends up being at a variable cfm rate, depending on distance, etc., bringing the make-up air in the same path would ensure the same flow rate, and if the make-up air fan stops, so does the vent (important, if this is really an issue!).

  27. Anonymous | | #27

    There is a very similar thread to this one for clothes dryers.

    Q: Do you think appliance manufacturers will begin solving this problem by supplying their own make-up air? For a clothes dryer this could mean a close-loop system, so that the dryer consumes air from outside, and ventilates used air back outside.

  28. Riversong | | #28

    UGH. There is so much foolishness around these issues because of excessive ventilation. The simplest systems still work the best.

  29. GBA Editor
    Martin Holladay | | #29

    You wrote, "What I would really like to see is a digital panel on the HRV that would provide several presets that unbalanced the fan to provide makeup air "

    The major problem with your suggestion is that the volume of makeup air required for a powerful kitchen exhaust fan is much more than required for ventilation.

    To meet ASHRAE 62,2 requirements, most homes only need to ventilate at 40 cfm to 100 cfm. So an HRV can be small and effective.

    If you need to provide 600 cfm or 1,200 cfm of makeup air for a kitchen exhaust fan, that's a whole different kettle of fish, requiring much larger ductwork.

  30. Chris Ladner | | #30

    Would a potential solution to this dilema be to install a a make-up damper and grille in the wall behind the stove (on a non-island application) and interlock the damper with the exhaust fan? This would simulate a commecial "compensating" hood by using the makeup air to "pick up" the odors, etc. and then be exhausted through the fan. As long as the pressure drop through the opening was small, the air being exhausted would not be drawn completely from the interior of the home. The only concern would be very cold days and the impact on the cooking area.

  31. GBA Editor
    Martin Holladay | | #31

    You are describing the standard solution to the problem: a powered makeup air unit. It's up to the builder or homeowner to decide if the makeup air needs to be conditioned. If the homeowner wants conditioned air, these systems get expensive fast -- and in any case incur a substantial energy penalty.

    Solutions to this problem are being discussed at length in postings to my recent blog, "Makeup Air for Range Hoods." As of this morning, there are 106 posted comments. Several posters have suggested variations of your solution.

  32. Chris | | #32

    Martin, thank you for bringing this very well deserved attention to this issue!

    One interesting thing about depressurizing, while we are on the subject.

    When something depressurizes your space, it potentially stirs up all sorts of stuff..not just backdrafted fumes, it So, in a building with a history, testing while performing depressurization can be used to unmask hidden facts about it

    If a building tests acceptably for fumes, ERMI (mold by QPCR), heavy metals, pesticides, etc. EVEN during a artificial depressurization "acid test", it even be healthy enough to live or work in!

  33. Chris | | #33

    Stacy, is there any chance that water from the moist kitchen air is condensing on something cold, like the bottom of the sink, and dripping? the best solution is getting rid of that moisture, but you also might want to look at insulating, in an airtight way, everything that might be a (cold=condensation) trap for moisture in the air. Outer walls, cold water pipes/plumbing, and the bottom surface of your sink.

    My sink came with insulation on its bottom. In the situation you describe, it might not take much to raise the temperature of anything water is condensing on above the dew point (and thereby prevent condensation)

    Also, once its dry, keep the cabinet doors shut to keep any moist kitchen air out. (and of course use your snazzy looking vent fan or HRV)

    I grew up around people who probably still think that leaky sinks are normal. They aren't.

    Buy a cheap digital thermometer with a relative humidity function (I've seen them for as little as $10 at some stores..) and see what the RH is down there over a period of time...

    If its more humid under your sink than in the kitchen, you probably either have a leak down there that you still have not discovered, or its against an outdoor wall that needs more insulating.

  34. aj builder | | #34

    Never really cared for heavy metal

    This thread has me head spinning like it's attached to a 1200cfm-er!

    Sounds like the multiple right ways should be culled and another blog posted with such.

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