Unused Clay Flue in Basement

[BTSomogyi]

Hello,
I've got a 8" OD (6.5" ID) clay flue pipe as a secondary flue that has never been used in my basement. The home was built in 1987, and it has a completely external block/stone chimney with an existing in-use (lined) flue for the living room fireplace.

The clay flue I'm wanting to use for a basement supplemental heat stove goes about 3' horizontally from an unfinished basement wall, then turns up for a 30' straight run through the masonry chimney. I'm looking to put a stove with a 6" exhaust into this flue. It is lined in pristine terra cotta flue liner. The flue liner comes out of the basement wall at 6' high (on center), and the floor joists overhead are at 8', but there is a bit less than the 18" required for single wall pipe to the plywood forms used in creating the hearth in the room above (see photo). I would go with double walled pipe to address this issue.

I saw in another post that exceeding 2x the area of the stove output is against code (due to slowdown of exhaust), but the 6.5" ID flue is only 42.25" cross-sectional area, vs the 28.25" of the 6" exhaust pipe, so this seems to be within spec. I was planning to use a 6" -> sq flue adapter with the double walled chimney pipe to hook up the stove.

I've attached photos, but I'm interested to know if there is anything described that is a red flag regarding use of this flue for a wood stove.

Best regards,
BTS

 

[begreen]

Sounds ok, but note that the flue gases are going to cool considerably over the 30 ft of flue. This may be ok for a furnace, but not good for wood stove flue gases containing creosote. Once the gases cool down to condensation point they will create creosote deposits. Burning dry wood will help as will running the stove with a high enough output temp so that the flue gases stay above 250º at the top of the chimney. Also, the chimney may be balky until it warms up. After that it may draft too strongly in which case a key damper may be necessary to keep the stove from overfiring.

 

[Wisco Shepherd]

I would tend to agree with @begreen you are going to want something that has pretty high exhaust temps fast in order to heat up that flue. Most modern stoves run best on insulated liners and that is a lot of Mass to heat up. maybe some sort of easy breather or something that can run a bit hot like a Pacific Energy or some sort of hybrid stove.

 

[EbS-P]

Are there square to round adapters?

 

[Ctwoodtick]

In addition to the other info provided already, I would question how pristine the mortar joints are in this almost 40 yr old flue. Although it’s never been used, time has still gone by.

 

[bholler]

The forms should be pulled from.the bottom of your hearth extension regardless