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Install Inline Backdraft Damper on Fan-in-a-Can

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NY2024
NY2024 Member Posts: 23
in Strictly Steam

Hi! One of my goals this Spring/Summer is to better air seal our house. My boiler room has a fan-in-a-can which lets in a tremendous amount of cold air when the boiler isn't running. I re-wrapped with foil wrap all the connections in the rigid metal vent to prevent air from leaking out from those connections (many of them weren't fully sealed). I am going to seal the penetration with spray foam where the rigid metal vent exits the rim joist (which currently lets in a huge amount of cold air). I was also thinking about sticking one of these spring-loaded inline backdraft dampers into the duct right behind the hood where it the duct exits to the outside.

Is there any reason not to do this? When the fan-in-a-can is triggered to operate by the boiler turning on, should the pull from the fan be enough to open the backdraft damper?

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Comments

  • pecmsg
    pecmsg Member Posts: 7,122

    If it's letting in large amounts of air with the boiler off the house may be under excessive negative pressure.

    I suggest a blower door test be performed to find and fix the issue.

    Mad Dog_2HydronicMike
  • Jamie Hall
    Jamie Hall Member Posts: 27,432

    I would be rather cautious. Yes, it will probably work — but I wonder how much or if it will restrict the airflow, or even possibly change air pressure in the boiler room.

    Also, I would want to know just how much the boiler depends on air from that source — or to put it another way, if something should prevent that damper from opening, would the boiler still have enough air to fire properly? If not, you'll need a safety switch on it…

    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • HVACNUT
    HVACNUT Member Posts: 7,482

    If the space warranted outside combustion air, it should only effect the space the combustion air is needed. Seal off the boiler room. Or build a boiler room. Then seal it.

    What type of heating equipment is there? Power burner?

  • Mad Dog_2
    Mad Dog_2 Member Posts: 8,578

    I concur with pecmsg. You have air-balancing issues. I've never seen a fan-in-the-can do that. Mad Dog

    Consulting by Mad Dog & Matt Jr.
  • ChrisJ
    ChrisJ Member Posts: 17,443

    @pecmsg is right.
    If air's coming in, air's going out somewhere, perhaps all over.

    The higher up the leaks are in the building, the stronger the effect they have in cold weather.


    Does your boiler have a damper on the flue?

    Single pipe 392sqft system with an EG-40 rated for 325sqft and it's silent and balanced at all times.

  • AdmiralYoda
    AdmiralYoda Member Posts: 798

    How old is your house? If it is old enough that there are leaks everywhere…you probably don't even need outside air. Warm air rises and is escaping higher up in the building envelope. That outside air source is an easy inlet to replace all of the air your house is losing. Chimney effect.

    My house was built in the 1860's. I've put new windows, blown in insulation, caulked a bunch of stuff, etc. It's about as tight as it can get for its age. No draughts or anything. Not much more I can do to tighten it up further unless I want to completely gut it and remodel with spray-in foam, etc.

    I have no outside air source in my basement. The boiler runs fine with the dryer, bathroom vent and kitchen vent hood blowing air to the outside.

    How does your boiler run without the outside air source?

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