Elbow Clearance to Ceiling?

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wjohn

Member
Jul 27, 2021
167
KS
Many of those installs may be with double wall pipe. Which in your case with 14' ceilings I would absolutely recommend.
Most of the ones I saw sure looked like single wall from the pictures. A few specifically mentioned single wall. It's the internet, though :)

Sorry, not 14' ceilings - 14' floor to chimney cap height. My ceilings are only 8'.
 

Highbeam

Minister of Fire
Dec 28, 2006
19,529
Mt. Rainier Foothills, WA
Have you ever measured diagonally from a single wall pipe on a proper install? The box itself acts as a shield.

I don't understand your question but the box is not a shield, it is a structural box to support the chimney and to maintain that 2" clearance to the class A from the joists/insulation/etc..

So now your interpretation changes. It's not "in any direction" but back to perpendicular.
 

Highbeam

Minister of Fire
Dec 28, 2006
19,529
Mt. Rainier Foothills, WA
I don't understand your question but the box is not a shield, it is a structural box to support the chimney and to maintain that 2" clearance to the class A from the joists/insulation/etc..

So now your interpretation changes. It's not "in any direction" but back to perpendicular.
Like this. This is ridiculous, you don’t measure the 18” “in any direction” it’s perpendicular.

92972C3B-2E31-47E6-BFC0-C86925B7D83D.jpeg
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
26,867
central pa
I don't understand your question but the box is not a shield, it is a structural box to support the chimney and to maintain that 2" clearance to the class A from the joists/insulation/etc..

So now your interpretation changes. It's not "in any direction" but back to perpendicular.
But is that box a combustible material? If it is in the way of the radiant heat coming off the pipe wouldn't it block that radiant heat?

If you don't believe talk to a few manufacturers about it. I have.
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
26,867
central pa
Like this. This is ridiculous, you don’t measure the 18” “in any direction” it’s perpendicular.
Where does it say that???
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
26,867
central pa
Most of the ones I saw sure looked like single wall from the pictures. A few specifically mentioned single wall. It's the internet, though :)

Sorry, not 14' ceilings - 14' floor to chimney cap height. My ceilings are only 8'.
Ok that's a big difference. What is the minimum chimney height requirements for your stove?
 

wjohn

Member
Jul 27, 2021
167
KS
Have you ever measured diagonally from a single wall pipe on a proper install? The box itself acts as a shield. And when we are talking about protecting from radiant heat how is the fact that it travels in all directions irrelevant?
I just measured on mine and you have about 9" from the pipe to the ceiling surface just outside of the box, at the shortest distance. The ceiling support box would have to drop down what, another 8-9" to make that diagonal 18", right? But this is kosher per the chimney system manufacturer, I presume because they have tested and the size of the dropped down box area adequately shields the surrounding ceiling material from the heat off of the pipe?
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
26,867
central pa
I just measured on mine and you have about 9" from the pipe to the ceiling surface just outside of the box, at the shortest distance. The ceiling support box would have to drop down what, another 8-9" to make that diagonal 18", right? But this is kosher per the chimney system manufacturer, I presume because they have tested and the size of the dropped down box area adequately shields the surrounding ceiling material from the heat off of the pipe?
It may be that they found in testing radiant heat at that angle is reduced enough to allow the lesser clearance. I don't know the pipe you are using. I am just going by what Olympia and Jeremiahs have told me about this issue.
 

wjohn

Member
Jul 27, 2021
167
KS
Ok that's a big difference. What is the minimum chimney height requirements for your stove?
VC says 16' from base of the stove is "ideal" and deviations from that may affect performance. I figure if I have issues I can add another section up top, but I'll have to support it if I go that high.
 
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Highbeam

Minister of Fire
Dec 28, 2006
19,529
Mt. Rainier Foothills, WA
I just measured on mine and you have about 9" from the pipe to the ceiling surface just outside of the box, at the shortest distance. The ceiling support box would have to drop down what, another 8-9" to make that diagonal 18", right? But this is kosher per the chimney system manufacturer, I presume because they have tested and the size of the dropped down box area adequately shields the surrounding ceiling material from the heat off of the pipe?
You are understanding the weird interpretation correctly but I think Bholler has it wrong. It's not measured diagonally but perpendicularly. Might be time to call the manufacturer.
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
26,867
central pa
VC says 16' from base of the stove is "ideal" and deviations from that may affect performance. I figure if I have issues I can add another section up top, but I'll have to support it if I go that high.
As long as you are aware you may need more pipe trying it isn't an issue
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
26,867
central pa
I just measured on mine and you have about 9" from the pipe to the ceiling surface just outside of the box, at the shortest distance. The ceiling support box would have to drop down what, another 8-9" to make that diagonal 18", right? But this is kosher per the chimney system manufacturer, I presume because they have tested and the size of the dropped down box area adequately shields the surrounding ceiling material from the heat off of the pipe?
I will say the manufacturers I use require the box to hang down more than the total height of your box. What chimney are you using?
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
26,867
central pa
It's ridiculous and wrong. You don't measure in any direction, you measure perpendicular to the pipe.
Again where does it say this? What manufacturer has told you this?
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
26,867
central pa
Absolutely radiant heat is less intense the further you go from perpendicular so at some point less clearance is certainly safe. I personally don't know at what angle that is so I can't say. But I feel saying you only need to worry about the clearance from perpendicular and ignore everything else is a very dangerous piece of advice.
 

Highbeam

Minister of Fire
Dec 28, 2006
19,529
Mt. Rainier Foothills, WA
Absolutely radiant heat is less intense the further you go from perpendicular so at some point less clearance is certainly safe. I personally don't know at what angle that is so I can't say. But I feel saying you only need to worry about the clearance from perpendicular and ignore everything else is a very dangerous piece of advice.
I wonder what an expert or the manufacturer would say. Surely, they don't just expect the installers to guess?

Here is one from google...."A single wall stovepipe must have a clearance to combustible walls and ceilings, measured at right angles to the pipe of at least 18 inches."

 

bholler

Chimney sweep
Staff member
Jan 14, 2014
26,867
central pa
I wonder what an expert or the manufacturer would say. Surely, they don't just expect the installers to guess?
I know what they say I have talked to several. Install the box as specified. And none have said only measure perpendicular. I am sure the clearance with straight pipe has been tested and is safe unless that box specifies double wall. But putting an elbow right at the box changes everything.
 

Highbeam

Minister of Fire
Dec 28, 2006
19,529
Mt. Rainier Foothills, WA
I know what they say I have talked to several. Install the box as specified. And none have said only measure perpendicular.

Here's another one from the duravent manual:

"CLEARANCE: 6” clearance to walls 8” clearance to ceiling Clearances are measured at a 90 degree angle to the pipe."


So obviously, you have misunderstood. I don't know what else to tell you.
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
26,867
central pa

bholler

Chimney sweep
Staff member
Jan 14, 2014
26,867
central pa
If only perpendicular measurements matter why do all instructions for shielding on single wall pipe and stoves tell you to measure in every direction and extent the shield untill clearances are met?
 

Highbeam

Minister of Fire
Dec 28, 2006
19,529
Mt. Rainier Foothills, WA
If only perpendicular measurements matter why do all instructions for shielding on single wall pipe and stoves tell you to measure in every direction and extent the shield untill clearances are met?

They are referring to radially in any direction. The measurement is to be made perpendicular to the pipe.
 
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bholler

Chimney sweep
Staff member
Jan 14, 2014
26,867
central pa
OMG, now I have to look it up for single wall too for you? I'll let you do that in your spare time.
Well considering we are talking about single wall I am pretty sure it's much more relevant. If we were talking about double wall pipe this wouldn't be an issue.