Chimney flue back drafting down the adjacent flue. Chimney extension?

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Deere-nh

Member
Aug 30, 2022
49
NH
Hello all, I have a three flue chimney. All three flues are at the same height. I use the middle flue the most and oncassion use the flue to the right as well. I have noticed when I use the middle flue I will get a back draft on the flue to the right.

I am looking to get a chimney top extension kit. Any recommendations on how they work? And if this would fix the problem? Thoughts on heights as well? I was goimg to go with 18" one. I don't live in a windy environment but was concerned if the wind would blow it over.

[Hearth.com] Chimney flue back drafting down the adjacent flue. Chimney extension?[Hearth.com] Chimney flue back drafting down the adjacent flue. Chimney extension?
 
It's a common problem. The smoke is back siphoning down into the lower floor chimney. An extension on the main floor flue will help.
 
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18" should suffice. That uninsulated section will cool down the flue gases quickly.
 
18" should suffice. That uninsulated section will cool down the flue gases quickly.
Does this pipe need to be insulated? I was trying to see if they made a terra cotta top plate that went to SS liner to a class A stove pipe but had no luck.
 
Anchor plates for conversion to class A exist in several brand lines and some have support systems for the liner available.
 
Does the extension need to be insulated or will I be fine without?
That depends on the setup and stove and operator. Do you know what the normal flue temps are?
 
That depends on the setup and stove and operator. Do you know what the normal flue temps are.

I dont. The woodstove is in a fireplace and am not able to get the thermometer at proper height. The stove temp is usually around 400 to 600.
 
How tall is the liner and is it insulated? What stove is this for?
 
The liner should be insulated, there's plenty of room and a lot of heat loss in 20' of uninsulated liner in a cold exterior chimney. If the brick chimney doesn't have at least 1" clearance from combustibles then insulation is required. It can be retrofitted by pulling the liner out.