Our chimney has two flues, one we use the other must have been for a woodstove in the basement but has since been covered up with a finished basement. When we burn in the fireplace we can smell the smoke downstairs and from what I've been told it's because air has to come into the house to replace the air going out the chimney and the path of least resistance is down the other flue so smoke comes back down and into the house. I think the easiest solution is just to seal off the flue from the top, is that right? If so how should I go about doing this?
What’s the best way to seal unused flue
fireplace
Related Solutions
There is no way to convert a gas fireplace to burn wood, unless you are very lucky and the gas fireplace is an insert in a properly functioning solid fuel fireplace (in which case you basically just remove the insert, and have the fireplace inspected).
In situations like this, you have a couple options.
Install a Solid Fuel Stove
This option will require the least amount of work, though can still be quite expensive and time consuming.
You'll have to follow all local codes that deal with this type of project, but for this example we'll use National Fire Protection Association (NFPA) standards (NFPA 211 Standard for Chimneys, Fireplaces, Vents, and Solid Fuel-Burning Appliances).
Clearances
You'll need 36" clearance from combustible materials on all sides (top, left, right, front, and back).
Floor protection
You'll need a floor protector under the unit, that extends 18" in all directions (except up/down, that would just be silly).
Listed Stoves
The floor protection requirements will be provided by the manufacturer, for listed stoves.
Unlisted Stoves
For unlisted stoves, the floor protection requirements are determined by the length of the legs on the unit.
0" - 2"
Stove must be placed on non-combustible floor.
2" - 6"
4" hollow masonry laid to provide air circulation through the layer, covered with 24-gauge sheet metal.
6" and Greater
Closely spaced masonry not less than 2", covered with 24-gauge sheet metal.
Reducing clearances
There are ways to reduce the clearances, by installing special materials around the stove. Check your local codes for methods to reduce clearances.
Stovepipe
You'll need 18" clearance around the stove pipe, as well as a stovepipe thimble where the stovepipe passes through walls/ceilings.
Chimney
If you don't have a proper masonry chimney to attach the stovepipe to, you'll have to use a factory built metal (A.K.A. prefabricated, Class A, all-fuel) chimney. You likely won't be able to use the same pipe used by the old gas fireplace. You also don't want to connect the stovepipe to the chimney used by your other gas appliances (furnace, water heater, etc.).
Build a masonry fireplace
If you've got the cash and time, you could have a proper masonry chimney/fireplace built (or build it yourself). This option will require modifications to the building structure, lots of masonry skills, a healthy bank account, and a good bit of time.
When I light my fireplace I leave my flue open for the night. The residual smoke from your fire is putting the smoke smell in the house when you close the flue
Related Topic
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- Brick chimney with no smoke chamber: is there some type of metal insert that would work instead of rebuilding inside of chimney
- What’s the deal with this (fake?) chimney on the house
Best Answer
You didn't mention what the opening was that the smell was entering the house with. If it is a thimble opening, you can block the opening with solid mineral wool insulation, cut to the size of the opening and fit snugly. This will stop the downward drafting. Add a thimble cap over the insulation and it will look fine. It also will stop cold air from entering the house through the flue.
You could also put a flat concrete patio block. cut to just larger that the flue opening, over the unused flue. You can secure it in place with some exterior masonry caulking. This will stop the drafting, but also make it possible to remove the cover if you decide to use the second flue for another purpose.