Making double-wall pipe

[EddyKilowatt]

The house I moved to has an old (pre-EPA) Jotul 8 that is direct-connected to a ten-foot masonry chimney, via a couple feet of horizontal 7" singlewall steel pipe and a blank-off plate in the damper throat. I've been musing that I might warm the flue and improve the draft a bit by sliding a two-foot piece of 8" pipe (which I have) over the 7" pipe, spacing the two with some 1/2" liner wrap I've got left over from the install at my previous house. Question, will the steel 7" pipe hold up in this kind of service... or would I need stainless to handle the temperature of an insulated inner pipe, at which point I might as well spring for commercial doublewall pipe?

thanks,
Eddy

 

[begreen]

First make sure that the horiz connection is heading uphill at least 1/4"/ ft. I think the stove would likely respond best with additional footage added to the top.

 

[EddyKilowatt]

I think the stove would likely respond best with additional footage added to the top.

Probably so... it's just that this double-wall experiment is something I can do with leftovers I have on hand (if the plain-steel inner pipe can take the heat that is). The draft's not bad; I got to top of the stove to 750F without really trying during a three-split test burn last week. I mainly want things warmer "on principle" to reduce condensation and creosote in the 13 x 13 flue in the chimney.

The connector is already inclined nearly an inch per foot, so I think I'm okay there... in fact due to the angle it was a bit fussy to get re-connected to the stove outlet.

Eddy

 

[fossil]

Your chimney flue cross-sectional area is more than four times that of the stove flue collar. This doesn't meet NFPA 211 standards even if the chimney's an interior one. Have you given any thought to a chimney liner? As to the pipe experiment, I think most commercial double wall pipe is stainless inside, but I'm no expert. I think it's more of a service life issue than a heat capacity one. Can't think of any reason why you shouldn't give it a try, though. Rick

 

[Ottowoops]

About 1979, I made my own double wall pipe by sliding a piece of 8" plain finish pipe down over a piece of 6" plain finish pipe and using a piece of lath to pack the space with Dow Corning ceramic fiber insulation that had the consistency of cotton balls. When the stove was going wide open, I could lay my hand on the pipe without getting burnt. After about eight years, I sold the house and tore the airtight out. The inner pipe was pretty well deteriorated from rust, but there was ZERO creosote because the temperature was always too hot for condensation to occur.

Ottowoops