Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Combustion Air?

This past July, walked into my utility room(which has always been described as "too small for my equipment") and it felt like a sauna. Lost story short, the assessment was a backdraft from my hot water heater . Very hot and humid that day, and the door to the utility room was closed like it typically is because my home is on a slab. In the utility room is a 70K btu atmospheric boiler, and 40k btu how water tank, along with electric clothes dryer and wash machine. I had numerous pro's over for quotes, was going to go with a HE system to eliminate any combustion problems, but because I may sell home within next few years, I elected to go with a "fan in the can". I live in RI......will this solve any lack of combustion air problems to this room? Room is about 13ftx8ft.


  • hot_rod
    hot_rod Member Posts: 21,880
    Consider a CO detector also.
    The entire venting and combustion air layout needs to be inspected by a qualified pro. You could have something in the flue piping causing inadequate draft?
    Backdrafting appliances can be a very serious issue.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    vinpalumbo1979delta T
  • vinpalumbo1979
    vinpalumbo1979 Member Posts: 5
    Yes, I now have a smoke/CO det in that room. I've been here for 5 years, and thats the only incident that I know of, but better safe than sorry. The CO detector is in, and the fan will be installed by a heating company that recommended this as an alternative to spending a lot of coin on a HE sealed system.
  • vinpalumbo1979
    vinpalumbo1979 Member Posts: 5
    And yes, both the flue and chimney were clear.
  • STEVEusaPA
    STEVEusaPA Member Posts: 6,506
    An energy star rated dryer can pull all the air out of a 1500 sq. ft. home in a 1 hour cycle. Best to bring in combustion air then have a qualified pro turn on your heater, all the appliances that can cause a back draft-dryer, exhaust fans, range hood, and check for back drafting.
  • vinpalumbo1979
    vinpalumbo1979 Member Posts: 5
    Thats the plan Steve, however, I know my fan will be wired to both the boiler and hw tank. If the dryer turns on, the fan wont activate. Its an electric dryer, but I also heard they use alot of air.
  • Jamie Hall
    Jamie Hall Member Posts: 22,952

    Thats the plan Steve, however, I know my fan will be wired to both the boiler and hw tank. If the dryer turns on, the fan wont activate. Its an electric dryer, but I also heard they use alot of air.

    It would be better if the dryer also activated the fan -- it doesn't matter whether it's electric or not; either one moves a lot of air. Or tries to. It will work better if it has enough air... Of course, without the fan I suppose it can get the air it needs by backdraughting through the hot water heater or the boiler... not ideal.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    JUGHNE Member Posts: 11,021
    I have done a "Fan in a Can" for a commercial water heater room that used an 8" inlet pipe. This was the medium sized fan, I believe. Hopefully the smaller one you might use would be quieter than the one I installed. If you are in the room when this one starts, conversation is limited......just mentioning this.....

    Also a question for other Wallies; how does this prevent a standing pilot water heater from firing until the pressurizing of the room is proven? Simple for electronic ignition of comm heaters......but a basic water heater with no electric connection??
    Please, someone tell me the control system for this.
  • Tim McElwain
    Tim McElwain Member Posts: 4,608
    Both Tjernlund and Field provide kits that can wire in all the equipment in the combustion zone so that if the fan fails nothing will operate. All appliances in the space must be interlocked.

    Be careful with Fan in the Can and Fan in the drum as you can over pressurize a room.

    Keep in mind dryers are not vented they are an exhaust system and require much more air than most appliances. ANSI 223.1 /NFPA 54 require make up air for Type 1 clothes dryers (residential).

    Once the air requirements are accomplished a combustion analysis should be done.
  • lchmb
    lchmb Member Posts: 2,997
    How about just a permanent opening into the room from the outside with a 4" or even 5" pipe? Drop it into a bucket to create an air trap...room needs air it come's in naturally...
  • vinpalumbo1979
    vinpalumbo1979 Member Posts: 5
    The fan that will be installed, has a 4 inch pipe, so it's def smaller than the one mentioned in the above post for a commercial application. I could have provided a permanent opening from the outside, and not used the fan, but these openings were recommended to be much larger that 4 or 5 inch. Everyone recommended the fan in the can as a solution, rather than spending a bunch of money on a direct vent system(selling house soon). I thought I had it figured it until Tim mentioned "over pressurizing the room". I will mention this to the tech. Lastly, I had no idea about the dryer being a problem, I do know that the boiler and hw tank will be wired in, but not the dryer.
  • captainco
    captainco Member Posts: 792
    110,000 btu needs approx. 55 cfm of combustion air. Usually when you install a fan in the can there should be a relief damper or barometric on the pipe indoors that only allows the proper amount of outside air and recirculates it with inside air. Combustion air pipes from outdoors can only work if the room is in a negative pressure. If the room has to be negative then the flues might not work either.

    With a simple draft tester combustion air can be verified. Put the draft gauge in the flue and fire the boiler or water heater. Then turn on the dryer. If the draft falls, you don't have enough air.