Elbow Clearance to Ceiling?

  • 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.

Highbeam

Minister of Fire
Dec 28, 2006
19,300
Mt. Rainier Foothills, WA
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.

So you think the measurement methods are different for single wall vs. double wall? Interesting.
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
26,053
central pa
They are referring to radially in any direction.
That isn't what it says. Now in most cases with a flat wall and straight pipe if you measure perpendicular everything else will be fine. But again simply saying perpendicular is the only measurement that matters for every situation is a dangerous suggestion.
 

Highbeam

Minister of Fire
Dec 28, 2006
19,300
Mt. Rainier Foothills, WA
That isn't what it says. Now in most cases with a flat wall and straight pipe if you measure perpendicular everything else will be fine. But again simply saying perpendicular is the only measurement that matters for every situation is a dangerous suggestion.

Regardless of the correct answer, this is a very good topic to discuss. I mean really. This is a profoundly misunderstood item that should be very obvious. Safety should be the top priority and we deserve a solid answer.

I'll certainly be happy to be wrong if there is a valid support that you don't measure pipe clearance perpendicular to the pipe axis.
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
26,053
central pa
Regardless of the correct answer, this is a very good topic to discuss. I mean really. This is a profoundly misunderstood item that should be very obvious. Safety should be the top priority and we deserve a solid answer.

I'll certainly be happy to be wrong if there is a valid support that you don't measure pipe clearance perpendicular to the pipe axis.
It is rare that anything will be closer than a perpendicular measurement. But I have had it occasionally with things like trim sticking out in a strange spot. Or with studs or floor joists in unfinished areas.
 

Highbeam

Minister of Fire
Dec 28, 2006
19,300
Mt. Rainier Foothills, WA
It is rare that anything will be closer than a perpendicular measurement. But I have had it occasionally with things like trim sticking out in a strange spot. Or with studs or floor joists in unfinished areas.

Thats why I posted that photo above. If the stove pipe was single wall it would have been too close to the ceiling at 9” when measured “in any direction”. Seems like a common install that would not be legal if we measured it “your” way.
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
26,053
central pa
Thats why I posted that photo above. If the stove pipe was single wall it would have been too close to the ceiling at 9” when measured “in any direction”. Seems like a common install that would not be legal if we measured it “your” way.
It isn't my way. It is the way I was told to measure clearances in all of my training courses and in discussion with manufacturers. Now obviously if you are dealing with a ul listed component like a chimney support box that over rides the generic clearances of non listed single wall pipe. That is why stove manufacturers can specify lesser single wall clearances. If the single wall was listed then you would need to honor theirs.
 

EbS-P

Minister of Fire
Jan 19, 2019
1,451
SE North Carolina
If you want to get in the physics here we really need to integrate or add up all the thermal radiation for the entire length of the pipe. This includes radiation that is perpendicular and as well as all the angles less that 90. The theoretical treatment would go all the way to 0 degrees. Not relevant here. What is, is the length of the pipe matters, the longer the section the more radiation a single point on the wall receives. So manufacturers must take into account all scenarios. Making clearances based on the length of the run is too difficult. We have rules and codes that must be interpreted. Maybe there should be additional statement saying If a section of pipe is shorter than xx” the clearance can be reduced by##%. Or we could say that any wall/ceiling penetration needs a certain length of pipe perpendicular to the penetrated plane before any bends. That seems simpler.

Is the original single wall configuration safe? Maybe. Is the double wall safer? Yes. Can you construct this system (single or double wall) so there is no argument that it conforms the minimum distance to combustibles. Yes. Do it that way.
 

stoveliker

Minister of Fire
Nov 17, 2019
1,867
Long Island NY
I doubt the "shorter than xx, clearance can be reduced" has a proper basis in physics. IR radiation goes down with the square of the distance in 3D. Hence a part of the pipe a bit farther away (b/c a longer pipe) contributes almost nothing to the heat load. In other words, the heat load on the nearby wall/ceiling is almost solely caused by the radiating part that is closest to it, because the distance goes linear, but the heat load goes down squared.

Also, the radiative intensity from an object (in particular one with a certain roughness, as in matte pipes) will depend on the angle of departure. Highest load is at 90 degrees, falling off to zero at a departure angle parallel to the surface. So for the section of pipe closest to the ceiling, where the departure angle of the radiation is closest to "parallel to the pipe surface", the intensity will be much reduced.

I do find "18" measured at right angles from the pipe" noted on the web - but not on authoritative websites, so I'd have to assume they copied properly from authoritative sources.
 

wjohn

Member
Jul 27, 2021
110
KS
Or we could say that any wall/ceiling penetration needs a certain length of pipe perpendicular to the penetrated plane before any bends. That seems simpler.
This is what I was surprised to not find anywhere. I would have expected a manufacturer to call out this situation (elbow right off of ceiling support). I know they can't cover everything in the install manuals but this isn't an uncommon thing to do.
 
  • Like
Reactions: bholler

kennyp2339

Minister of Fire
Feb 16, 2014
6,090
07462
This is what I was surprised to not find anywhere. I would have expected a manufacturer to call out this situation (elbow right off of ceiling support). I know they can't cover everything in the install manuals but this isn't an uncommon thing to do.
I think thats why ceiling support boxes are not mounted flush to the ceilings and why some are pretty long, allows them to be mounted lower into the room incase you need to do the elbow thing, most of the time its easier to plan for a straight shot up from the stove collar to the ceiling support then if you need to add a bend, do it with the class A pipe above and use metal strapping to anchor it.
 

begreen

Mooderator
Staff member
Nov 18, 2005
90,417
South Puget Sound, WA
The OP defined the concern in his first posting. The question is about heat being radiated directly above the elbow if its surface is beyond the protective shielding of the ceiling support box. He provided a clear diagram of the area of concern. The easiest solutions for peace of mind are either to add a 6" stub at the support box to lower the elbow or to use double-wall stovepipe.
 
  • Like
Reactions: bholler and EbS-P

brenndatomu

Minister of Fire
Aug 21, 2013
6,537
NE Ohio
If its an issue in this install, why not fabricate a simple heat shield to stand 1" off the top of the elbow?
Still not enough distance?
I agree though, just use doublewall!
 

Highbeam

Minister of Fire
Dec 28, 2006
19,300
Mt. Rainier Foothills, WA
If its an issue in this install, why not fabricate a simple heat shield to stand 1" off the top of the elbow?
Still not enough distance?
I agree though, just use doublewall!
Double wall is really nice to work with and lasts a very long time. I'm glad I have it in the house and am considering upgrading from single wall in the shop once prices come back down.