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Blower door tests and fireplaces

Most of the blower door tests that are mentioned on GBA give numbers under 3 or 2 or 1 ACH50. I'm guessing that none of these homes have a traditional fireplace. How much does a traditional fireplace with standard chimney damper contribute to air exchange numbers? What are some recommendations for improving a house with fireplace and chimney?

Asked by Derek Roff
Posted Sep 1, 2014 7:54 PM ET


5 Answers

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The leakage of a standard masonry chimney damper at 50 pascals is in the range of 40-400 cfm.

I base that on one conversation with my blower door guy.

Plug it with an inflatable stopper http://www.batticdoor.com/DraftStopper.htm

Answered by Kevin Dickson, MSME
Posted Sep 2, 2014 4:30 AM ET

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Kevin mentioned the Battic Door Chimney Pillow. A similar product from the U.K. is the Chimney Balloon.

Here's the thing, though: if you care about energy efficiency, you're not going to want to have a traditional fireplace in your house. When you have the time to address this problem seriously, you can demolish the chimney and fireplace (start at the top). You'll end up with more interior space.

Answered by Martin Holladay, GBA Advisor
Posted Sep 2, 2014 5:15 AM ET

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What would you suggest to minimize the impact of a fireplace on a building's energy efficiency short of removing it or not including one in a new build? I ask from the viewpoint of wanting to/planning on using wood as the primary source of heat (using a woodstove).


Answered by Rob Shuman
Posted Sep 2, 2014 9:39 AM ET

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Martin, you are absolutely correct about my not wanting to have a fireplace in my house. My sweetheart, however, loves the ambiance of a small fire on a winter's day. I have protested that 'ambiance' seems to mean smoke, carbon monoxide, and unburned hydrocarbons, since these fireplaces don't function very well. That didn't sway the argument, nor did the floorspace advantage. But the discussion is ongoing. If anyone can offer further reasons in support of removing the fireplace, I would love to hear them.

"It might hurt resale" is another common statement. I've never wanted to make my living choices based on the hypothetical taste of an unidentified future buyer, but real estate agents live by this myth. I'm guessing that more buyers ten years from now will be wanting the energy efficiency and floor more than the ambiance of a fireplace.

Answered by Derek Roff
Posted Sep 2, 2014 9:57 AM ET

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Bob: Gasketed flue-top fireplace dampers (eg: http://www.homesaver.com/content/locktop/about_locktop_dampers.aspx) are far more air-tight than the typical cast-iron/steel dampers located at the firebox.

Masonry chimneys on exterior walls are not usually insulated- a big R2-ish hole in your insulation. This can be remediated with exterior rock wool insulation and non-combustible furring/siding.

Masonry chimneys often have no air-sealing where they go through the attic insulation plane, which can be remediated with sheet metal air-barriers sealed with fire-rated duct mastic.

Answered by Dana Dorsett
Posted Sep 2, 2014 10:04 AM ET

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