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How to prevent leakage through the range hood?

user-6323668 | Posted in Green Products and Materials on

We are building a net zero house and are concerned that leakage thorough the range hood will be a major loss of conditioned air or gain of unconditioned air. Is there a device to install where the duct exits the house that will close tightly when the hood is not in use?

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  1. GBA Editor
    Martin Holladay | | #1

    The device is called a backdraft damper. Most exterior terminations for range hood fan ducts include a backdraft damper.

    Backdraft dampers aren't airtight, for technical reasons. (They need to be able to open easily when the fan starts up.)

    Some Passivhaus builders don't install a range hood fan that is ducted outdoors. Instead, they install a recirculating range hood fan with a charcoal filter. In addition, they install an exhaust grille in the kitchen ceiling (far from the range). The exhaust grille is connected to the exhaust system of an HRV.

    Check with your local building inspector before you adopt this approach.

    -- Martin Holladay

  2. charlie_sullivan | | #2

    Most backdraft dampers for range hoods are junk, and I don't think it's for any reason other than manufacturers cutting corners on items that not many homeowners or builders pay attention to.

    But good ones do exist. For the 3.25 x 10 rectangular size, this Canadian product is excellent:

    I could detect no air leakage through it in my blower door test. And its construction is head and shoulders above that of supposedly reputable brands such as Broan. I did seal some seams in its construction myself, so it might not have been quite as air tight straight out of the box.

    I think that last time this came up here there was also a recommendation for a round-duct version that worked well.

    1. zenhomes | | #15

      Here is a well-made round damper available in many sizes -

  3. GBA Editor
    Martin Holladay | | #3

    Thanks for the product suggestion! I really appreciate it.

    I have made a note of it -- so that hopefully, next time this question comes up, I'll remember your recommendation.

    P.S. When tested with a blower door, this type of backdraft damper looks pretty good during a depressurization test -- but usually it looks much worse on a pressurization test. When the wind is blowing against the wall that has the termination, the backdraft damper will probably work well. When the wind shifts, and the termination is on the leeward side of the house, my guess is that the backdraft damper will allow some exfiltration.

    -- Martin Holladay

  4. JC72 | | #4

    You can look into installing an inline motorized damper behind the gravity damper at the exterior wall. Just make sure you can access it when it eventually fails and needs to be replaced. Of course you'll have to use round pipe ducting (which you should be using anyways instead of that rectangular garbage).

    On a side note, don't spend a ton of money on a high BTU gas range because you'll have to install a more powerful fan for the range hood which in turn will then require additional ducting for makeup air. Consult your local building codes.

  5. brp_nh | | #5

    What kind of range are you installing, I would imagine standard electric or induction? What are your cooking habits? Steak in a cast iron pan every night....or do you lean towards lighter cooking?

    If your answers are electric and "lighter cooking", I would seriously consider a re-circulating hood and then you won't have to deal with makeup air and draft issues.

    Although we wired for it and can put one in if needed, we opted for no range hood at all...because our range is electric and our cooking habits are light. Grease isn't an issue and the ventilation system can handle any moisture. The house probably smells like pizza for a couple hours after baking one, but that's a good problem.

  6. Reid Baldwin | | #6

    This is a timely thread for me. We have been noticing cold air around our range lately. I haven't specifically noted how it correlates to wind, but it has been windy lately. We have a microwave over our range that provides the vent fan function. I considered installing a motorized damper but I don't know how to tap into an appropriate electrical signal that would open it whenever the fan is on. Any advice on that?

  7. jackofalltrades777 | | #7

    Is there a good damper that would work on a 5 or 6 inch round duct?

  8. walta100 | | #8

    This Tamarack Cape damper, looks very interesting seems to be silent effective and no electric required.

    Has anyone seen or used this product this product?


  9. Anon3 | | #9

    Try this? It's magnetically sealed, you'd have to add the weather stripping yourself.

    From what I read before, cape damper don't seal completely.

  10. GBA Editor
    Martin Holladay | | #10

    The Cape damper is a great product, but it is not really appropriate for a range hood exhaust duct. Range hood exhaust ducts are subject to grease buildup. The grease buildup can be a problem for many types of dampers, but the fabric in the Cape damper makes it a particularly poor choice for this application.

    -- Martin Holladay

  11. user-5293988 | | #12

    I am making this decision at the moment in our house. In the past when installing range hoods with a 3.25"x10" duct that goes directly out the back of the hood through the wall, I have had difficulty sealing the hood to the duct: First the duct is installed in the wall (carefully sealed), but when the hood is installed to the wall and duct, it seems impossible to tape the hood to the duct and thus providing a somewhat leaky installation - does anyone have a better way?

    Alternatively it seems like the better sealed option is to do a short vertical of the 7" (or other appropriate size) round duct and then install a 90 and go out the wall (with an american aides or similar quality backdraft damper). The disadvantage of this is the elbow which decreases hood efficacy that is really not needed. Most range hood manufacturers include a converter plate to switch between 3.25" x 10" and round ducts.

    I agree that the Imperial Damper noted previously looks like it is well made, though I haven't tried it. I i could figure out the duct sealing dilemma, I would go this route.

    American Aldes makes round dampers that are high quality with spring damper and epdm gaskets for sealing. But they don't make one to fit a 3.25 x 10" duct.

    Cape backdraft dampers are silent, and work well in a strong breeze or gust. But in a gentle wind, I think air can still pass through them.

  12. Matthias_32 | | #13

    A great vent seal, 4" round duct, I've used them on microwave/range exhaust, bathroom fans, and dryer vents. One of the best out there,perhaps the best.

    1. GBA Editor
      Martin Holladay | | #14

      The Heartland termination works, but eventually the plastic cap deteriorates from UV exposure. (It happened at my house.) I'm not sure that this termination is a good idea for range hoods, where grease build up is a problem.

      1. Matthias_32 | | #16

        The UV deterioration issue is quickly prevented with a coat of paint. I paint them anyway to match the siding.

        Grease buildup has never been a problem in the couple dozen I've installed over the years for homeowners. I do mention to them they should check it periodically and clean them if they become sticky.

        The simple gravity design of this termination is one of the most effective designs I've found.

  13. Hawnes | | #17

    anyone know where he got this product from?

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