New Stove and a draft question

[jbrown56]

First I would like to thank those who offered their thoughts on my stove question. On Saturday I purchased a Jotul Oslo 500. I've had my old steel stove for 26 years and heats my house so well that I'm a little nervous about the new stove. In talking to my salesman he asked me what kind of chimney the stove will be exhausting into. I told him it is a 8 x 12 masonry. He told me that I may lose some efficiency because the stove was rated with a 6" round chimney. I know that I have good draft because when I light a match in a cold stove it pulls the flame from the match head. Also my chimney is on the inside of the house. Any thoughts you can offer me on this issue will be greatly appreciated.

Jim

 

[elkimmeg]

Code wise you situation is compliant with a direct connection Opperating most efficiently ,Well! that might be the best question to discuss. Also cleaning that stove might mean pulling it out and removing the damper plate. th old beast probably flooded that 8/12 flue with heat the New Oslo is trying to keep heat in the stove and as little as possible going up the chimney

that said it is anyone's guess as to how well t your Oslo will preform with a direct connection Maybe the question should be asked what percentage of performance hit are you willing to accept

10 20 30% or more. I do know the members here that had direct connections and them lined their chimneys reports huge performance gains Used less wood and gained more control of their stoves

 

[zzr7ky]

Hi -

I would line it with 6" rigid liner. You'll have a nice easy to clean, easy to light and manage, high performance package!!

ATB,
Mike P

 

[jpl1nh]

Code wise you situation is compliant with a direct connection Opperating most efficiently ,Well! that might be the best question to discuss. Also cleaning that stove might mean pulling it out and removing the damper plate. th old beast probably flooded that 8/12 flue with heat the New Oslo is trying to keep heat in the stove and as little as possible going up the chimney
that said it is anyone’s guess as to how well t your Oslo will preform with a direct connection Maybe the question should be asked what percentage of performance hit are you willing to accept
10 20 30% or more. I do know the members here that had direct connections and them lined their chimneys reports huge performance gains Used less wood and gained more control of their stoves

I have a very similar situation with my Woodstock Keystone though its a 7" pipe with 1 90 degree elbow going directly into a thimble that goes into a tile lined 6"x10" chimney located in the center of my house. Elk, is the potential problem that JB has too much draft due to the chimney size or too little draft due to the chimney size. Could you elaborate please? Also JB do you connect with a thimble connection or is it an open hearth with a block off plate? (and does thimble vs block off plate matter)

 

[senorFrog]

I have a jotul oslo and had some marginal draft last year. They stove may work okay, but not optimally. Meaning you may not be able to damper it down and get the long burn times or get better efficiency with the secondary burn tubes. How tall is your current chimney and is it mostly internal on the exterior of the house. Also, how many 90*'s and is there a horizontal run of pipe?

I think I'd be inclined to line it, but you could always do that later on.

Check out my marginal draft issues w/the oslo. Hopefully they are fixed this year because I installed an exhausto fan.

https://www.hearth.com/talk/threads/4008/
https://www.hearth.com/talk/threads/2965/

 

[Gooserider]

The problem with these chimneys is the cross sectional area of the flue compared to what the stove needs. The flue is actually the "engine" that drives the entire system to produce heat. It does so by the hot exhaust gasses rising up the chimney, pulling fresh combustion air into the stove. To do this, the gasses need to stay hot, and move fairly quickly so they don't have a chance to cool. The hot gasses want to expand, and the only place they can do so is to rush out the top of the stack, which helps drive the flow. Exhausting into a liner the same diameter as the stove exit keeps the gasses moving, pulling fresh air into the stove, and carrying any remaining unburned creosote out of the chimney before it has a chance to cool and condense on the flue walls. Insulating the liner improves this even more by helping to keep the gasses as hot as possible. (An insulated liner also improves safety in the event of a chimney fire)

When you vent into a larger cross section chimney, the gasses have room to expand, which looses some energy right there, the gasses cool when they expand, and are further cooled by contact with the chimney walls (which will take a LONG time to really get hot, assuming they ever will...) which makes them less "anxious" to escape out the top, and gives them a chance to drop any creosote they may be carrying... This leads to a slower exhaust and a weaker draft, which in turn will make a less enthusiastic stove that potentially puts out less heat and requires more wood to keep it going.

The old smoke dragons didn't have a big problem with this, as they tended to dump a lot of excess heat up the chimney, so you got a fairly decent draft regardless. Part of the improvement of a modern stove is to put less heat up the chimney, sending it out into your room instead. Mostly this is a "good thing" but one of the negative consequences is to make the new stoves fussier about their chimneys as they are ideally only sending enough heat up the stack to keep an efficient chimney working, and don't have the same "margin" of excess energy to drive an oversized stack.

Current code says you MAY NOT have a stack with a cross section area more than 2X the flue collar diameter on an external chimney, or 3X on an internal chimney, and it reccomends that the area be the same as the flue collar all the way up, which usually means a liner when dealing with an existing chimney.

(BTW, I may not have the physics part exactly right, but it's a workable first pass, and the conclusions ARE valid...)

Gooserider

 

[jbrown56]

Gooserider, thanks for the great explanation on my question. You put it in good layman's terms. I guess I will bite the bullet and put a liner in as it would defeat the purpose of the new stove without it.

Jim

 

[zzr7ky]

You're going to really like it!
SB