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Community and Q&A

Hot basement

DenK | Posted in Mechanicals on

I have just moved into a home with a wood burning furnace hooked up to the NG furnace and duct work. When I run the wood furnace (wf) the basement gets really warm. Should I cut a register into the cold air trunk? Thank in advance for any suggestions.

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  1. charlie_sullivan | | #1

    I can think of two possible reasons. One is that the body of the furnace is not very well insulated and it directly heats the basement (assuming it's in the basement--is it?). The other is duct leakage. That could be a poorly sealed duct in some part of the ducting that is just used for the wood furnace, including the connection of the ducts to the furnace. Are there dampers that control which furnace is connected to the duct system? Or just backdraft dampers in the section for each furnace?

    Ducts are often poorly sealed, and it wouldn't be a bad idea to do a round of duct sealing whether or not that is the particular problem here. Use mastic, not tape.

    More on testing duct leakage:

  2. GBA Editor
    Martin Holladay | | #2

    The reason that your wood-burning furnace is making your basement hot is that most wood furnaces are poorly insulated. It's also possible that your wood furnace is oversized for your house, or that building even a moderately sized fire in the furnace's firebox is putting out more BTU/h than your house needs.

    Charlie's suggested solution -- sealing the duct seams -- may help a little. You might also try insulating the exposed sections of supply-air ductwork. I doubt whether these measures will make a significant difference, but they can't hurt.

    There may be no easy fix to this problem. You can try lighting smaller fires, but you may just have to learn to live with the situation.

    Q. "Should I cut a register into the cold air trunk?"

    A. No. The "cold air trunk" is more properly called a return-air duct. This duct brings air from the conditioned space (the rooms upstairs) to the furnace to be heated. It is not designed to supply cold air.

  3. wjrobinson | | #3

    I say enjoy the warm floors along with the heat is helping your home even though it is below.

  4. Expert Member
    Dana Dorsett | | #4

    What AJ said, but it's important to insulate foundation walls to reap the full benefit, or you're burning through quite a bit of wood that you would not otherwise need to.

    If the basement is more than 5F warmer than the room above you can move quite a bit of heat via convection by keeping the stairwell doors open.

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