Damper in double wall pipe

  • Active since 1995, Hearth.com is THE place on the internet for free information and advice about wood stoves, pellet stoves and other energy saving equipment.

    We strive to provide opinions, articles, discussions and history related to Hearth Products and in a more general sense, energy issues.

    We promote the EFFICIENT, RESPONSIBLE, CLEAN and SAFE use of all fuels, whether renewable or fossil.
Ashful

Ashful

Minister of Fire
Mar 7, 2012
19,983
Philadelphia
I’m planning to install a key damper in a double wall pipe, in the next few days, and wondering how to handle the usual compression spring. Here’s what I have:

9c6d660128d92cbf4b74803987241ae7.jpg

So, that spring on the axle near the handle will be compressed so hard it’ll likely deform the outer wall of the double-wall pipe, if I just drill the usual 1/4” hole and insert the rod. What I seem to be seeing, at least in a few cases, is folks counter-boring the outer wall large enough to allow the entire spring and cup washer to penetrate thru to the inner wall. So, the damper fits as if it were in single wall.

72ce006d259868a0d60ebc0623243d1b.jpg

This would have the added advantage of making easier to thread the bent axle thru the pipe.
 
Last edited by a moderator:
The damper is designed for single wall pipe. Is there a reason to not buy the proper fitting as shown in the lower image?
 
I haven't done this, but have thought about it, and have seen examples of others doing so.
Buy a 6" & a 7" damper (an 8" might work with mod)
Use the key part of the 7" & the cast iron part of the 6"

You used to be able to buy the 7" size, not sure now. Putting a longer spring on an 8" key would probably work as well. (Or stretch it, or washer it)
Just an idea, that I have seen done.

The ONLY reason I haven't tried this, is my chimney is very short & I'm afraid the damper would restrict the flow enough that I might have draft issues in warmer / shoulder season weather. The damper, even vertical does restrict flow / draft quite a bit -- I've seen figures between 15-20%.
 
Last edited:
begreen said:
The damper is designed for single wall pipe. Is there a reason to not buy the proper fitting as shown in the lower image?
Click to expand...

This is a highly “engineered” piping assembly, made up of about 7 pieces of double wall to make the required precise translation from my stove up and back to my liner at block-off plate. I really don’t want to go thru re-engineering that whole mess, if I can avoid it, and was aiming to put the damper in an existing 30” section of pipe.

Besides, is there anything at all different between the purchased damper section in that lower image, and what I’m planning to do? It looks like that’s exactly what they did, there.
 
Is there a slip section of stove pipe in the system where the damper could be inserted?

Like bcrtops indicated, I think the mandrel would need to be sized to the larger OD of the pipe while the damper sized to the inner ID of the pipe.
 
Just curious @Ashful
Do you have a problem with excessive draft?
I ask only because I was able to address this on our Jotul Oslo installation by restricting the OAK which seems way simpler than installing a damper in the flue.
 
begreen said:
Is there a slip section of stove pipe in the system where the damper could be inserted?

Like bcrtops indicated, I think the mandrel would need to be sized to the larger OD of the pipe while the damper sized to the inner ID of the pipe.
Click to expand...
No slip section. No issue with buying the larger size to steal the mandrel, if they're interchangeable. As I remember, this 6" one was dirt cheap at Tractor Supply Co.

semipro said:
Just curious @Ashful
Do you have a problem with excessive draft?
Click to expand...
LOL... are you new here? Yes, my draft is more than 3x BK's "allowable maximum" number. I'm into "voided warranty" territory, on this one chimney. Got a bit of a height issue, you see:

P6200036.JPG

I'm speaking of the 4-story job on the right, but you can also see the shorter chimney on my other Ashford on the left in this photo. Unfortunately, with 20" thick mud-stacked (not slang, the bedding mortar is literally mud from the back yard) stone walls all 'round, there's no chance of an OAK.
 
Ashful said:
LOL... are you new here? Yes, my draft is more than 3x BK's "allowable maximum" number. I'm into "voided warranty" territory, on this one chimney. Got a bit of a height issue, you see:

View attachment 221786

I'm speaking of the 4-story job on the right, but you can also see the shorter chimney on my other Ashford on the left in this photo.
Click to expand...
Haha. I don't spend much time in the Hearth Room, so yeah.
So why not restrict the inlet instead, i.e. install an Oak on the your BK and control that? Seems simpler maybe?
I've operated the Jotul 12 and Oslo and know it can be done with them under high draft. Not sure about the BK though.

What an incredibly cool house BTW!
 
Last edited:
Interesting.

My local "useless" dealer that just started selling BK products said that if I install my new (potential) Chinook on a 25' chimney, BK might void the warranty due to the excessive draft.
He also said, if I run it through the wall and out on the side of the house, I will run into creosote issues and will also void the warranty.

Plus, he has never heard of a steel cat!! Chris, you might take notice.....
 
Diabel said:
Interesting.

My local "useless" dealer that just started selling BK products said that if I install my new (potential) Chinook on a 25' chimney, BK might void the warranty due to the excessive draft.
He also said, if I run it through the wall and out on the side of the house, I will run into creosote issues and will also void the warranty.

Plus, he has never heard of a steel cat!! Chris, you might take notice.....
Click to expand...
Voiding the warranty may have been the wrong words, but his advice is sound.
 
webby3650 said:
Voiding the warranty may have been the wrong words, but his advice is sound.
Click to expand...

Pssst... webby, there is actually a statement in the owner’s manual that, “draft above 0.06” WC will void warranty.” However, I have never known BK to refuse support on this basis.
 
Ashful said:
Pssst... webby, there is actually a statement in the owner’s manual that, “draft above 0.06” WC will void warranty.” However, I have never known BK to refuse support on this basis.
Click to expand...
I know, I was referring more to the tee system.
 
Ashful said:
Pssst... webby, there is actually a statement in the owner’s manual that, “draft above 0.06” WC will void warranty.” However, I have never known BK to refuse support on this basis.
Click to expand...

Bk has spoken up when errors are found in the manual or website and indicated intention to fix them. Notice that this 0.06” thing is not being deemed a mistake? Wtf? 15’ of vertical chimney required but only 0.06” allowed. Is this even possible without a key damper?

The “useless” dealer above knows that the warranty is void above 0.06” makes me think there might have been a dealer bulletin. That’s pretty excellent for any dealer to have noticed otherwise.
 
  • Like
Reactions: Ashful
FWIW I ran a key damper on my 26’ stack and it didn’t improve much, I actually took it back out. I was hunting down another issue but did have smoke smell with it in. That was on my former 2 season old door gasket though. Still get the faint sweet smell above the door if i have to much smoke in the box for the cat to process. I hope your results are different.
 
Last edited:
Let’s be clear. I’m running two BKs, and have been for three years. I do NOT have a smoke smell issue, as long as I burn dry wood. The only time I have been able to generate smoke smell is when I burn wet wood.
 
Highbeam said:
Wtf? 15’ of vertical chimney required but only 0.06” allowed. Is this even possible without a key damper?
Click to expand...
I agree, this seems an impractical narrow range. However, I don’t think this is just BK, I think there are some industry/EPA testing standards upon which they’re leaning, here.
 
Ashful said:
I'm speaking of the 4-story job on the right, but you can also see the shorter chimney on my other Ashford on the left in this photo. Unfortunately, with 20" thick mud-stacked (not slang, the bedding mortar is literally mud from the back yard) stone walls all 'round, there's no chance of an OAK.
Click to expand...
Problems on the west wing?;)
 
Ashful said:
there's no chance of an OAK.
Click to expand...
I don't think I made myself clear but the real problem is in accepted terminology.
I was not suggesting you install an "outside air supply'.
I was suggesting you install whatever fitting is needed on the stove to connect to an outside air supply (typically called an "outside air kit") and that you restrict the airflow going into the stove from inside your house with some sort of adjustable restriction at that fitting.
I am not suggesting you need to bore a hole in an outer wall.
I know this works in overdraft situations because I've done it with our Oslo

Edit: the fitting at the arrow below. .

upload_2018-1-28_19-8-53.png
 
Last edited:
Thank you, @semipro. That might be something to consider, and you're right, I was misunderstanding you.

In related news, the key damper, manometer, and probe thermo are now installed:

IMG_4359.JPG IMG_4366.JPG IMG_4367.JPG

So, now... well, chit. What do you do when you have the key damper completely closed, and your chimney still pulls harder than 0.06" on a partial load of four small splits?
 
  • Like
Reactions: Easy Livin’ 3000 and begreen
Ashful said:
What do you do when you have the key damper completely closed, and your chimney still pulls harder than 0.06" on a partial load of four small splits?
Click to expand...
Restrict the flue outlet using some sort of chimney cap - perhaps a cable operated one?
56301128-175px.jpg


My suggestion of restricting the stove inlet would only increase the flue vacuum but it may lower actual flow rate. It kind of depends on whether you'r trying to reduce flow rate or vacuum. I understand that BK has related warranty issues with the latter.
 
  • Like
Reactions: Ashful
Ashful said:
What do you do when you have the key damper completely closed, and your chimney still pulls harder than 0.06" on a partial load of four small splits?
Click to expand...
After that damper is in there for a while it will soot those holes up and work better for ya...BTDT...
 
  • Like
Reactions: Ashful
semipro said:
Restrict the flue outlet using some sort of chimney cap - perhaps a cable operated one?
View attachment 221940

My suggestion of restricting the stove inlet would only increase the flue vacuum but it may lower actual flow rate. It kind of depends on whether you'r trying to reduce flow rate or vacuum. I understand that BK has related warranty issues with the latter.
Click to expand...


Not keen on that one, I know they default to "open" but chit happens.
 
Ashful said:
Thank you, @semipro. That might be something to consider, and you're right, I was misunderstanding you.

In related news, the key damper, manometer, and probe thermo are now installed:

View attachment 221936 View attachment 221937 View attachment 221938

So, now... well, chit. What do you do when you have the key damper completely closed, and your chimney still pulls harder than 0.06" on a partial load of four small splits?
Click to expand...
Pull the 6" liner and reinstall a 4 or 5"? Think of all that extra room you'll have in the chimney! Plus, nothing is more fun than climbing on top of that pitched roof, say, about 40' up off the low side?

That 30' insulated 6" liner will sell easily on Craigslist, long as it's not too banged up from it's experience.
 
Ashful said:
Thank you, @semipro. That might be something to consider, and you're right, I was misunderstanding you.

In related news, the key damper, manometer, and probe thermo are now installed:

View attachment 221936 View attachment 221937 View attachment 221938

So, now... well, chit. What do you do when you have the key damper completely closed, and your chimney still pulls harder than 0.06" on a partial load of four small splits?
Click to expand...
Put a second damper in or reduce the size of the holes through the damper
 
  • Like
Reactions: Ashful
You must log in or register to reply here.

Similar threads

RustyShackleford
single-wall stove pipe collecting debris
Replies
31
Views
2K
The Hearth Room - Wood Stoves and Fireplaces
RustyShackleford
RustyShackleford
F
8" Double Wall stove pipe fit Hutch Rebel
Replies
1
Views
388
Classic Wood Stove Forums (prior to approx. 1993)
begreen
begreen
R
Help! We have drips of goo running down on outside of double wall onto Blaze King stove.
Replies
3
Views
1K
Blaze King
Highbeam
Highbeam
matt382
Help with connecting new double wall pipe to existing chimney?
Replies
2
Views
1K
The Hearth Room - Wood Stoves and Fireplaces
matt382
matt382
T
Brief Overfire Flue pipe Explanation
Replies
6
Views
2K
The Hearth Room - Wood Stoves and Fireplaces
travelerstro
T
Top Bottom
Back