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Community and Q&A

Could a powered zone damper prevent leaks in a bathroom or kitchen exhaust?

SteveDraft | Posted in Energy Efficiency and Durability on

Spring or gravity backdraft dampers prevent air from coming into a house through kitchen or bathroom exhaust ducts, but they can let air out when the exhaust fan is off.   When air goes out through the backdraft damper, it’s letting air in somewhere else in the house.  These dampers just make the exhaust duct a one way hole in the house instead of a two way hole.

The closing force on spring or gravity backdraft dampers must be minimized to reduce obstruction of air flow.  Because fairly low forces are involved, the damper may get stuck open or closed when moisture, dust, or grease collect in the exhaust duct. 

A powered damper would ensure that the damper only opens when the exhaust fan is running, and it greatly reduce the chance of a stuck damper.   A Larson damper/fan combination is mentioned in some other questions on GBA.

 Are there any other powered dampers for exhaust ducts that aren’t blower/damper combos?   Many different HVAC powered zone dampers and fresh air  intake dampers are available.  Could a powered zone damper like this Suncourt be used on a kitchen or bathroom exhaust?

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  1. Expert Member
    BILL WICHERS | | #1

    I don’t see any reason you couldn’t use this damper in the application you describe. You’d want the “power open / spring close” configuration, and then wire it through a 24v control transformer parelleled with the fan so that the damper will open whenever the fan is running.

    Very large dampers similar to this in concept are commonly used in generator rooms. These would be the “spring open / power close” type so that they will open when the power fails so that the generator can run. I don’t like spring dampers for this application since they are less reliable as you mentioned.


  2. Expert Member


    Since you are obviously interested in this, let me suggest a further complication to improve things.

    Sick of poorly sealed fan boxes, inaccessible dampers, and the work needed to switch out an exhaust fan if newer model come along, on a house I built two years ago we instead mounted a large plywood box in the ceiling, with the duct sealed through 0ne end. The box was air-sealed to the drywall, and sized to be covered by a commercial ceiling grill. There was room inside for the fan, it's mounting box, and an inline damper to replace the flimsy one that came with the fan.

    Doing that would make mounting and servicing your motorized setup a lot easier. Aesthetically I prefer the larger commercial ceiling grill to the ones that come with most bathroom fans too.

    Full disclosure: I was able to do it that way because I was the contractor. I've never managed to convince a builder on the projects I design to repeat the experiment.

    1. SteveDraft | | #4

      This is probably the core of this issue. There aren't better dampers for kitchen and bathroom exhausts because builders have little incentive to fix the problem right. Though spring or gravity backdraft dampers let air out of the house when the wind blows, homeowners don't realize that it's the source of a problem because the outside air that replaces the lost air comes in at other locations. Likewise, homeowners wouldn't value your box solution until long after the builder has been paid.

  3. Expert Member
    Akos | | #3


    There are also 120V versions ( also old mid efficiency boilers have them on the exhaust if you are looking to scavenge one) which you can slave to your fan switch to open automatically when turned one. I would stay away from louver type vents as they don't seal (at best they discourage airflow).

    I think this is one of those where just one more electrical item that can fail. I think effort is better spent on getting one of the better sealing vents (I have the Broan ball type, almost no leakage) or install an inline butterfly valve.

    1. SteveDraft | | #5

      Thanks for the ideas Akos.
      I got interested in this when installing a Fantech butterfly damper.
      Though it is well made, the closing springs are so delicate that it's very likely to get stuck in real world conditions. I have to think that a well made powered damper would be more reliable.

      I found this fairly negative review of the Broan ball type damper.
      I guess it's one vote for and one against.

  4. Expert Member
    Peter Yost | | #6

    hi Steve -

    I have used and love the Cape May backdraft damper by Tamarack Technologies:

    Great products, excellent tech support, great family business here in the US.


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