One of my first construction jobs in Vermont, back in the late 1970s, was at an architect-designed home with a massive brick chimney with four flues: one flue for the oil-fired boiler, and three flues for the home’s three wood stoves. The chimney worked fine — mostly because the house had so many air leaks that the wood stoves were never starved for combustion air.
Massive chimneys like the one I remember from that job are expensive to build, but they are often a source of pride for the owner. They provide interior thermal mass; they are durable; and they are handsome to behold.
Older cold-climate homes often included similar large brick chimneys with multiple flues. This type of chimney is usually located near the center of the house, so that the bricks and the flues stay as warm as possible.
These days, however, this type of chimney is responsible for a variety of problems. It turns out that massive brick chimneys perform poorly in a modern airtight house.
I recently had a conversation with a builder about problems in a new home with a three-flue brick chimney. Each flue served a separate wood-burning appliance. I’m going to present the case in the form of a dialogue. (Full disclosure: a few details have been changed to protect the privacy of the people involved.)
Makeup air is pulled down one of the flues
Q. When one of the wood stoves in this home is operating, makeup air seems to enter the house through one of the unused flues of the chimney. The entering air has a sooty smell. I realize that the problem is due to the fact that the house is relatively airtight. What’s the solution?
A. That’s a tough one. If a house…
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