Hey guys new here and looking for some info. I have an old fireplace that I want to put a pellet stove in, was gonna go wood but my flue is to narrow and oval pipe cost to much, but pellet uses 3-4 inch so it’ll fit better. Now my question is my chimney has a double flue I’m assuming ones for fireplace the other for old boiler that no longer exists and that flue is not being used. When I drop the liner down the one flue and run to the stove what do I do with the other flue? I’d assume the liner would give nice airtight seal but the other flue would creat a draft. Do I cap both flues and block off the one or is it fine to just let it draw air? Thanks for any help
2 flue question
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Ctwoodtick
Minister of Fire
My non-pro thought is that a new pellet stove install would be fine and not affected by other flue that is not in use.
If the 2 flues exit at very similar heights at top, that may cause some exiting exhaust from pellet stove to go back down a bit into the boiler flue. Capping the boiler flue top may be needed.
For point of reference, I have the same set up you’re describing but with a wood insert and the other basement flue not in use. No issues aside from a tiny hint of smoke in basement but very rare and insignificant. My draft is so-so but my the chimney height is on the low side.
If the 2 flues exit at very similar heights at top, that may cause some exiting exhaust from pellet stove to go back down a bit into the boiler flue. Capping the boiler flue top may be needed.
For point of reference, I have the same set up you’re describing but with a wood insert and the other basement flue not in use. No issues aside from a tiny hint of smoke in basement but very rare and insignificant. My draft is so-so but my the chimney height is on the low side.
Capping is best; keeps weather and critters out.
Second option is to close the unused flue off at the bottom with one of those balloon inflatable flue blocking things. Less heat going up or cold air coming down there.
Or do both.
Second option is to close the unused flue off at the bottom with one of those balloon inflatable flue blocking things. Less heat going up or cold air coming down there.
Or do both.
Dont know if it’s normal but both flues are same in height and go to the firebox I guess it’s called, there identical just one side they tapped into at some point for boiler and hot water heater don’t know if I can get in there to block bottom but I can def close the top off. Was afraid of it causing smoke to come back down
Yes,. it's common for smoke to siphon back into a neighboring flue.
If both are in use, extending the used one by a foot or so helps.
But the one not in use is best closed so nothing gets in from the top. And I would see if you can close it from the bottom too.
If both are in use, extending the used one by a foot or so helps.
But the one not in use is best closed so nothing gets in from the top. And I would see if you can close it from the bottom too.
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