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Fan in a Can and Cold Air

I have a Field Controls Fan-in-a-can that was installed this summer to bring in added air for my burner. The basement is now cool instead of warm and cold air comes in all the time.

Is there supposed to be a damper to close the duct when the burner is not running?
Steve from Denver, CO


  • I,,,

    don't know of one that's specifically designed for the fa in the can but I imagine one could be adapted to serve the prupose. It should be interlocked of course so the burner won't run unless it's open.
  • Brad White_191
    Brad White_191 Member Posts: 252
    There are

    in-line spring and gravity-inclined dampers with low air pressure drops made for that purpose. They do not need motors so there is no interlocking needed.

    EFI sells them as does Fantech. EFI also has the "cape style" fabric damper which collapses under no mechanical airflow.

    Personally, I like spring-loaded Fantech type first and the "Artis" type dampers second. I often specify two in series for a double-block. Just make sure that your fan can overcome these. It should but it depends on the extent of your ducting.

    You are finding the paradox of energy efficiency- insulating piping and adding mechanically interlocked combustion air makes the basement cooler, not warmer. You are doing something right.
  • Steve Garson_2
    Steve Garson_2 Member Posts: 708

    When you say I am doing something right, can you clarify?

    Was the warm air from the house previously being blown out the chimney and now outside air is being used. Is the net result less wasted heat? Or more?
    Steve from Denver, CO
  • Charlie from wmass
    Charlie from wmass Member Posts: 4,314

    Less wasted heat and cleaner combustion. the boiler area maybe able to be enclosed to isolate it from the rest of the basement to lessen the effect of the fan in a can. Make sure what ever you do the damper is installed with the proper flow direction for the air. Also on high wind days you may still have air infiltration when the fan is not running. The damper in the fan-in-a can is also to be adjusted for the requirements of the unit it is supplying so as to not bring in more air than is needed for combustion. This is in the installation manuel with the fan unit.
    Cost is what you spend , value is what you get.

    cell # 413-841-6726
  • Bob Bona_4
    Bob Bona_4 Member Posts: 2,083
    no, no

    damper, just preset intake air volume requirements depending on specific appliance scenarios.

    Really, it was made for enclosed boiler rooms so that ambient air changes don't affect conditioned spaces. Imagine having a 4" hole in your wall in the family room :)

  • DrPepper
    DrPepper Member Posts: 29
    This is for combustion air...

    ...and we are recommending dampers to block the opening? Proving controls and roll-out switches or not it's still CO. Why was it installed in the first place? Is it providing combustion air to a power vent or atmospheric burner? Was it installed via ductwork close to the burner, or 20 ft away?

    Is there anything sensing or adjusting inside/outside pressure differential?

    If it is a fixed cfm fan what happens when the kitchen & bath fans and the dryer are all running?

    I don't know much about Field Controls, I mostly do commercial design. For me it is closed combustion or a CAI damper with interlock. Just trying to understand.
  • Jamie_5
    Jamie_5 Member Posts: 103
    pressure differential?

    I am trying to understand the concern here. Unless I am missing something, the only way a draft blocking device that would normally work with the combustion air fan (the "fan in a can") would not permit enough air to enter the combustion zone would be if the outside pressure became significantly *lower* than the inside pressure. Since other fans in the house would presumably only serve to potentially lower the *inside* pressure, what is the worry here?

    I'm not trying to be difficult. I'm just having trouble visualizing the potential problem.
  • Bob Bona_4
    Bob Bona_4 Member Posts: 2,083
    it's about

    cold air flooding the space with or without the FIC on.

    When the FIC is on, that's what is going to happen-nature of the beast. Only recourse is to enclose the appliance/FIC and seperate it from conditioned space-which is exactly why the FIC exists.

    When the FIC is off, though, I can see a possible need for a motorized damper to shut off the outside air. (remember, the FIC is interlocked with the burner(s). If anything, to keep vermin from getting in?

    But, reality sets in...A damper is one more thing to fail, create liability, add cost and complexity. I'm sure Fields Controls have a good reason why they don't have this.
This discussion has been closed.