Single vs double wall flue pipe

Gunfixr

New Member
Jan 14, 2019
89
Va, USA
OK, so I did search for threads on single wall vs double wall flue pipe for wood stoves. I found several, but none addressed the question I have.
So, the question is, is there a difference in the efficiency of a wood stove, in particular an epa stove, with single wall or double wall flue? Does the insulating layer increase the flue's draft efficiency? I know it will radiate less heat into the room, I know it costs more than single wall, my question is only about how it affects the stove's operation.
 

lsucet

Minister of Fire
May 14, 2015
1,552
San Ysidro, New Mexico
Both works fine but with some stoves double wall is better. those stoves tend to have low flue temp and is better to use double wall. Draft issues with some setups too, double can help. Another important detail is clearance. Double wall allows you to set up your stove closes to the walls etc, if your stove is shielded also.
 

SpaceBus

Minister of Fire
Nov 18, 2018
2,776
Downeast Maine
I too have questions on this topic. Before next heating season I'd like to change out my single wall to double wall with two 45's and out an insulated liner in my oversized clay tile liner. I already have a very strong draft and the stove tends to burn hot and fast, and that's with a 90 bend on single wall that rarely goes over 200f surface temp. The stove also has five 90 degree turns built into the smoke path. Is it possible to install a damper on double wall?

I look forward to next season when I have a probe in the stack!
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
18,638
central pa
I too have questions on this topic. Before next heating season I'd like to change out my single wall to double wall with two 45's and out an insulated liner in my oversized clay tile liner. I already have a very strong draft and the stove tends to burn hot and fast, and that's with a 90 bend on single wall that rarely goes over 200f surface temp. The stove also has five 90 degree turns built into the smoke path. Is it possible to install a damper on double wall?

I look forward to next season when I have a probe in the stack!
Yes you can get dampers for double wall
 
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lsucet

Minister of Fire
May 14, 2015
1,552
San Ysidro, New Mexico
I too have questions on this topic. Before next heating season I'd like to change out my single wall to double wall with two 45's and out an insulated liner in my oversized clay tile liner. I already have a very strong draft and the stove tends to burn hot and fast, and that's with a 90 bend on single wall that rarely goes over 200f surface temp. The stove also has five 90 degree turns built into the smoke path. Is it possible to install a damper on double wall?

I look forward to next season when I have a probe in the stack!
Yes there is key damper for double wall and are real cheap and easy to install. Also there is stove top adapter built in damper if you dont want to be opening holes on the stove pipe.
 

SpaceBus

Minister of Fire
Nov 18, 2018
2,776
Downeast Maine
Yes you can get dampers for double wall
Thank you.

Yes there is key damper for double wall and are real cheap and easy to install. Also there is stove top adapter built in damper if you dont want to be opening holes on the stove pipe.
Here's a photo of my flue collar. Are you saying I can get a damper that can fit the flue collar?
20190221_115526.jpg

If so, that would be perfect.
 

lsucet

Minister of Fire
May 14, 2015
1,552
San Ysidro, New Mexico
Thank you.



Here's a photo of my flue collar. Are you saying I can get a damper that can fit the flue collar?
View attachment 241213

If so, that would be perfect.
I recommend you ask @bholler. the one i use is the same brand of my stove pipe. I have on one setup the adapter and a key damper on my other setup on the pipe. I do like better the one on the pipe.
 

maple1

Minister of Fire
Sep 15, 2011
9,920
Nova Scotia
OK, so I did search for threads on single wall vs double wall flue pipe for wood stoves. I found several, but none addressed the question I have.
So, the question is, is there a difference in the efficiency of a wood stove, in particular an epa stove, with single wall or double wall flue? Does the insulating layer increase the flue's draft efficiency? I know it will radiate less heat into the room, I know it costs more than single wall, my question is only about how it affects the stove's operation.
You say flue pipe.

But do you actually mean stove or connector pipe?

Flue usually means chimney. And not in the room.
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
18,638
central pa
Thank you.



Here's a photo of my flue collar. Are you saying I can get a damper that can fit the flue collar?
View attachment 241213

If so, that would be perfect.
It usually works better if the damper is 12" or so from the stove. But with your stove it may not matter as much
 

SpaceBus

Minister of Fire
Nov 18, 2018
2,776
Downeast Maine
It usually works better if the damper is 12" or so from the stove. But with your stove it may not matter as much
Do you think a damper would be beneficial for my install? I wish this stove had an adjustable secondary intake to compensate for the tall chimney.
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
18,638
central pa
Do you think a damper would be beneficial for my install? I wish this stove had an adjustable secondary intake to compensate for the tall chimney.
If you are already running that cool on the surface of your pipe probably not.
 

Gunfixr

New Member
Jan 14, 2019
89
Va, USA
You say flue pipe.

But do you actually mean stove or connector pipe?

Flue usually means chimney. And not in the room.
Sorry, still new at this. I thought chimney was exterior, flue interior.
Yes, stove or connector pipe, the one in the room.

The chimney is double wall, duravent double wall, stainless, with screened(?) cap, also stainless. Ceiling box is duravent triple wall/insulated.
 

Gunfixr

New Member
Jan 14, 2019
89
Va, USA
Stove is Englander nc-13. At the chimney ceiling box, the pipe is 18.5" or 19" from the wall. Tapers back to about 16" or 17" down at the stove. Instead of running an extra wide or angled wall shield up, I took 8" pipe, split it, and mounted it over the 6" pipe, on the back 180 degrees. I used the same ceramic spacers used for wall shields.
Wall behind will get warm, but not hot.
I added the little side shields because the walls on either side got hot enough I didn't much care for it. You could leave your hand on it, but it was pretty hot.
The pipe is angled because the roof above has a peak which goes back, and putting the box where it is avoided having to mess with that.
2956cf62ff9e2281e5f0c072896fa2e2.jpg
 

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SpaceBus

Minister of Fire
Nov 18, 2018
2,776
Downeast Maine
If you are already running that cool on the surface of your pipe probably not.
Well, I could run it hotter, but I feel like it might damage the stove. At the hottest part it will run up over 700 in a hurry if I chase flue temps.
 

Highbeam

Minister of Fire
Dec 28, 2006
16,222
Mt. Rainier Foothills, WA
I own a duravent double wall damper equipped appliance adapter. It's the first little 6" chunk of pipe you stick into the stove, comes with a key damper installed or without, and then you drop additional sections of double wall pipe right into it. Some stoves need an appliance adapter and some don't.
 

Highbeam

Minister of Fire
Dec 28, 2006
16,222
Mt. Rainier Foothills, WA
Well, I could run it hotter, but I feel like it might damage the stove. At the hottest part it will run up over 700 in a hurry if I chase flue temps.
If the surface temperature of a piece of single wall is 200 when the stove below is over 700 then I suspect that you have a broken thermometer. Or, since 200 celsius equals almost 400 Fahrenheit you might be reading celsius. 400 would be about right for a 700+ stove.
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
18,638
central pa
If the surface temperature of a piece of single wall is 200 when the stove below is over 700 then I suspect that you have a broken thermometer. Or, since 200 celsius equals almost 400 Fahrenheit you might be reading celsius. 400 would be about right for a 700+ stove.
His stove is a 2 tiered moroso. They do a very good job of extracting heat from the fluegases. In my opinion to good of a job
 
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Highbeam

Minister of Fire
Dec 28, 2006
16,222
Mt. Rainier Foothills, WA
So, the question is, is there a difference in the efficiency of a wood stove, in particular an epa stove, with single wall or double wall flue? Does the insulating layer increase the flue's draft efficiency?
Since warmer flue gasses make a stronger draft you get a stronger draft by keeping the flue gasses warm with the double wall.

Stove efficiency is unaffected by single wall vs. double wall unless you have so much single wall that your draft is reduced below your stove's required threshold. At some point your draft can be so low that the fire doesn't burn well. At some point you can cool flue gasses so much that creosote formation can be excessive.

Total system efficiency can actually be improved with single wall. Poorly designed stoves send a lot of heat up the flue in an effort to burn clean or to be simple. If you can recapture some of that heat, but not too much, with single wall pipe then it contributes to total system efficiency. Most wood furnaces have a back and forth flue arrangement on top of the firebox that they call a heat exchanger where room air steals heat from the flue gasses.

I have 10 feet of single wall above my noncat and I wish I could steal some heat from it. My noncat stove dumps too much heat up the stack. It's safe and works well but I know that there is heat being wasted.
 

SpaceBus

Minister of Fire
Nov 18, 2018
2,776
Downeast Maine
His stove is a 2 tiered moroso. They do a very good job of extracting heat from the fluegases. In my opinion to good of a job
I had very little creosote in the pipes when I cleaned them a month ago. That added to the expected accumulation from the total winter is probably less than a gallon from a 25' system. Obviously not amazing, but should improve when I get double wall and an insulated liner. There's not much advice on this particular stove out there.
 

BethelStrong

Member
Dec 12, 2018
146
Ohio
I’ve been holding back on asking this same question (1st season install). I have doublewall stovepipe, but was considering going to single wall next season. The double stovepipe is one of those adjustable types, I assume just a shield really, and no insulation. I ended up not needing the clearance reduction (or is it gain?). Am I wasting too much heat? My stove heats my house well enough, sometimes too much (when that happens, on comes the furnace circulator to bring cold basement air up or hot air down).

Quadrafire Millennium 3100 EPA
6 feet of Chimney
5 feet of Stivepipe
No temp probe
No stovepipe damper


Sent from my iPhone using Tapatalk
 
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Gunfixr

New Member
Jan 14, 2019
89
Va, USA
That is one point, I put in single wall to get the heat.
I've got more than enough. I end up trying to run smaller fires, and less air, and it won't run well. Bigger fire, more air, it runs well, but I end up running lots of fans and opening windows.
My wood isn't the best, so i'm not sure how much is because of that.
 

Highbeam

Minister of Fire
Dec 28, 2006
16,222
Mt. Rainier Foothills, WA
I’ve been holding back on asking this same question (1st season install). I have doublewall stovepipe, but was considering going to single wall next season. The double stovepipe is one of those adjustable types, I assume just a shield really, and no insulation. I ended up not needing the clearance reduction (or is it gain?). Am I wasting too much heat? My stove heats my house well enough, sometimes too much (when that happens, on comes the furnace circulator to bring cold basement air up or hot air down).

Quadrafire Millennium 3100 EPA
6 feet of Chimney
5 feet of Stivepipe
No temp probe
No stovepipe damper


Sent from my iPhone using Tapatalk
I would keep the double wall. It's good stuff, stainless steel inner wall so it should last as long as the chimney. Welded and the double wall acts as both a heat shield and insulation to keep flue gasses warm and creosote accumulation down.

Both work but I think it's a downgrade to go to single wall in a normal home application.
 
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maple1

Minister of Fire
Sep 15, 2011
9,920
Nova Scotia
I would keep the double wall. It's good stuff, stainless steel inner wall so it should last as long as the chimney. Welded and the double wall acts as both a heat shield and insulation to keep flue gasses warm and creosote accumulation down.

Both work but I think it's a downgrade to go to single wall in a normal home application.
Plus, that's a pretty short chimney.