Put SS liner through old fireplace flue vs. old furnace flue?

[Chuck-OH]

Hi. I've been lurking here on and off for a while, considering adding a wood stove for supplementary heat. I've got a two story home built in the 40's with a walkout basement. The basement has an exterior chimney and a large FP which I don't think was ever used much. Chimney guy looked at it and said it looked "pretty good."

The same chimney though has another flue next to it, which opens into the basement only via a 7.5 inch metal pipe. It was the exhaust for the original gas furnace, which is long gone. It's sealed, though I could easily unseal it.

I know that if I put a wood stove in front of the FP, I will need to install a SS liner up the chimney. My question though is whether the old furnace flue could/should be used instead. The old furnace was gas, so I know wood smoke/exhaust never went up that chimney. I don't know though how far the 7.5 inch pipe goes up the chimney though. Would using it depend on the size and condition of the pipe? Or does any new woodstove require a SS liner, and not an old sheet metal liner?

Or, if there's a reason not to use the old furnace flue, please let me know. Just trying to plan ahead.

Thanks

 

[Hogwildz]

Hi. I've been lurking here on and off for a while, considering adding a wood stove for supplementary heat. I've got a two story home built in the 40's with a walkout basement. The basement has an exterior chimney and a large FP which I don't think was ever used much. Chimney guy looked at it and said it looked "pretty good."

The same chimney though has another flue next to it, which opens into the basement only via a 7.5 inch metal pipe. It was the exhaust for the original gas furnace, which is long gone. It's sealed, though I could easily unseal it.

I know that if I put a wood stove in front of the FP, I will need to install a SS liner up the chimney. My question though is whether the old furnace flue could/should be used instead. The old furnace was gas, so I know wood smoke/exhaust never went up that chimney. I don't know though how far the 7.5 inch pipe goes up the chimney though. Would using it depend on the size and condition of the pipe? Or does any new woodstove require a SS liner, and not an old sheet metal liner?

Or, if there's a reason not to use the old furnace flue, please let me know. Just trying to plan ahead.

Thanks

What size is the fireplace flue?
A 6" s.s. liner can be tough in a 7-1/2" flue. If the tiles are not set flush with each other, or the mortar between has oozed out prior to setting, the liner has a tendency to catch on these things in a tight space.
Most manufacturers suggest a full s.s. liner for best draft and chimney protection in case of fire. Of course depending on the liner you would need to insulate to achieve the code for fire protection (for flex liner & uninsulated rigid). If you went with insulated double wall rigid, no further insulation would be needed. If tiles is in good shape as you gas furnace should be, then technically you don't need a liner(check you local code first) or insulation.
But, being on an outside wall, your draft might suffer due to it being colder and losing/transferring more heat easier. If the old fireplace chimney is also in good shape you could direct connect there also. but again possibly suffer draft problems(lack of). If the fireplace tiles are larger, I myself would go fully lined with insulation. I went with insulated double wall rigid on a mostly interior chimney and the draft is excellent. But that is just my preference. Also keep in mind with a direct connect (lined only to first lower flue tile) you will have to pull the insert out every time you clean to get at the smoke shelf area, which is where a lot of the soot & ash will land when it is swept. With a full liner, most stoves you can pull the baffle, tubes or baffle board and sweep directly into stove. That alone is a major plus to consider.

 

[Chuck-OH]

Thanks Hogwildz. I think I follow your meaning, though I might be a little too new to this to grasp all of what you're saying.

I don't know if the 7.5 inch pipe terminates inside a masonry flue, or continues all the way up. I guess I'd need to unseal it and try to look/feel inside.

Regarding the drafting issue, I did build a fire in the basement FP once, and the updraft was incredible. It was in the 30's outside that day.

It's about 31 feet from the floor of the basement firebox to the top of the chimney.

 

[Chuck-OH]

To answer about the FP flue, I haven't measured it, but the chimney sweep said it was "unusually large."