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Should a wood burning fireplace (with outside combustion air intake) pull auxiliary convection air from outside or inside the home?

Andrew Homoly | Posted in General Questions on

I have purchased a Quadra-Fire 7100FP Wood Burning fireplace for my new home. It has an “Auxiliary Convection Air” feature that can be routed to the outside or as a cold air return to another part of the home. I am assuming this should be routed as a cold air return inside the home so as to not bring in outside air in that will then pressurize the home. What do you think?

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    Andrew,
    Read this article and then let us know if you have further questions: How to Provide Makeup Air for a Wood Stove.

  2. Andrew Homoly | | #2

    Martin,

    I believe this article did not answer my question. This article refers to "combustion air" which I agree should be brought into the firebox directly from the outside for several reasons. My fireplace has this so I do not anticipate any pressure issues in the home due to combustion air makeup needs.

    My question involves "auxiliary convection air" or the air which is brought in around the firebox and then gets blown out the top area into the room with blowers. My fireplace has 3 options for this air. It can either come in the bottom of the front panel, through a duct that can be routed to the outside, or through the same duct that can be routed to the other side of the room to form a "cold air return" line so to speak. My fireplace company says they always hook this line up straight to the outside, but they really don't know why. It seems to me this is a bad idea for 3 reasons:

    1. Bringing in outside air that theorectically does not go out of the home would pressure up the home (it actually says this in the owners manual like this might be a good thing).

    2. When the fireplace is not on, cold air can just migrate into the home through the fireplace (although a damper will mitigate this if we remember to shut it when the fire burns out).

    3. Creating a "cold air return" line might create a nice heating circulation pattern in the room/home where the hot air coming out of the fireplace would then go to the ceiling, go across the celing, and then come down to the air intake vent on the other side of the room.

    Which method would you chose... getting this auxiliary air from the outside or from a cold air return line?

  3. John Klingel | | #3

    If I am reading this right, this is effectively a stack robber, right? All it does is bring air from the immediate area (if that is what you choose), heat it, and send it flying back at you, but hotter. Correct? I don't see any pressure issues or anything else to worry about with that method, so that would be my selection. The only thing that I can see that is remotely possible is that the stack temp may drop, and there is a critical temp there to avoid/minimize crap accumulating in the stack (350 degrees??). Have you read on hearth.com? That is what they do over there; wood. Note: I am just a diy guy here.

  4. GBA Editor
    Martin Holladay | | #4

    Andrew,
    Assuming that you are describing the situation correctly, and that the air in question is not combustion air, then I agree with John Klingel. It sounds like the fan in question is simply circulating interior air around the outside of a heat exchanger to warm up the air. It makes sense to use indoor air for this purpose.

  5. David Meiland | | #5

    Sounds like the fireplace installers are creating big air leaks wherever they go. If I understand your description, this "auxiliary convection air", if ducted from the outside, comes straight into the house, passing across the outside of the firebox as it comes in. As long as the fireplace is burning, this air may not seem cold, but there has got to be an energy penalty associated with it. I don't see why you'd duct it at all--just let it enter under the stove and exit at the top, using interior air in the immediate vicinity of the stove. I suppose you could duct to a "cold" area of the house and try to create an airflow pattern, but how do you know it will work?

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