Minimum Clearances to Single and Double Wall Pipe

[sbedelman]

Hi,

I did a search but wasn't exactly clear on how to apply the discussions to my situation. Please excuse me if this was covered and I missed it.

We are looking to install Rais 106 in a new house (soon to be sheetrocked). The flue will run straight up through the ceiling and out. The ceiling/roof is very low slope (1:12). there is no attic.

The design for the structure is quite simple, almost stark so ideally we would have the least amount of "stuff" up at the ceiling. In doing a web search I came up with the various minimum spacing between the stovepipe for both single and double wall, plus the reduction permitted if the surface is non-combustible although I don't fully understand how they apply when the pipe exits vertically rather than horizontally.

My first question is what materials qualify both as a practical matter (I won't set the house on fire if I use it) and legal matter (meets code) as non-combustible? I see Hartiboard, cement board and Wonderboard mentioned as possibilities but I wasn't able to locate what if any UL or other rating would be required to be sure any one material meets the code definition of non-combustible. Anybody know?

Since the design calls for the ceiling to be of one look if there is non-combustible material it would be great we could use a few sheets of it above the stove, do the rest in sheetrock and be able to skim coat the whole thing so that it all looked the same. This raises the further question as to whether or not the skim coating or paint would blow the rating on any material that was otherwise considered non-combustible?

Ideally we would use single wall pipe from the stove up to the ceiling box (because Rais makes really nice looking single wall pipe), have an noncombustible ceiling and a very small and simple transition box at the ceiling permitting the minimum set back from the pipe to the ceiling. What I am not sure of is what that setback would be at the collar (sorry I don't know the proper terms) for both single and double pipe. Of course I would be using an approved ceiling mount kit not just running the pipe through ceiling.

Any help would be appreciated. Thanks.

 

[elkimmeg]

I think you are a bit confused and need clarifications first of all single wall pipe clearance to combustiables is 18" and that is in all directions We are talking about the pipe th extends fron the flue collar into a chimney Meaning Class A chimney in your case Double wall connector pipe distance to combustiables is set by the manufacturer usually 6"

From you ceiling box it you extend the Class a chimney pipe down from the ceiling 18" then connect single wall pipe that is the correct way. You may reduce that distance of class a to 6" if you use double wall connector pipe, What you have to use at the ceiling level. is the the clearance ceiling box system specified with you '''class A chimney pipe. You must also use the roof flashing and ventilated boot.

 

[sbedelman]

Ok, got it. That all makes sense. But I thought I read that if the ceiling is made of non-combustible material (or is that not suitable shielding?) the 18" pipe clearance from the single wall pipe to the ceiling is reduced by 50%. Rule 14 in link below...

(broken link removed to http://www.woodheat.org/safety/rulesforfluepipes.htm)

Am I reading the drawing correctly? And if so would that mean if I had a non-combustible ceiling and a ceiling box with a class A chimney extending down into the room it would only need to extend downward 9" from the face of the ceiling (assuming they make such an animal)?

We are trying to configure the ceiling box to avoid the 18" wide pipe as the architect would prefer to avoid the look of a narrow pipe flaring out to a wide one. Pictures of this stove from the Rais catalog show a rather small ceiling plate both in diameter and thickness which is quite nice looking. This is probably an installation from Europe and the vendor of the ceiling box/Chimney etc almost certainly either hasn't designed it to US code or even if it does meet code they have haven't had it certified since they don't sell here.

From your post (thank you by the way) I see that double wall reduces the minimum separation to 6" but the problem is that Rais doesn't make double wall pipe and says this is because double wall doesn't look very good on this stove (I am still trying to figure out if this is try and if so why).

Assuming there really is a compelling reason to use single wall we are looking for techniques (like a non-combustible ceiling) that allow us to reduce the depth or diameter of whatever has to extend down from the ceiling while of course still being safe and meeting code.

Any suggestions would be most appreciated.

Thanks.

 

[sbedelman]

I got to the engineering support person at Selkirk and when I asked the minimum distance from a standard sheet rock ceiling to a single wall vertical pipe the answer was....

3 1/2"

Boy was I surprised. But according to them NFPA 211 table 6-5.1.2 states that the 18" spacing is to be measured perpendicular to the pipe. So while a vertical pipe has to be 18" from a wall the only requirement at the ceiling is that that (in the case of a sloped ceiling) the class A chimney protrude 3 1/2" below the sheet rock.

This contradicts what is on a number of web sites and what our installer thought but apparently the confusion comes from drawing that show the chimney extending below the ceiling 18" in structures with steep slopes. This is required not for vertical spacing but horizontal. A 45 degree pitch roof needs and 18" drop get get 18" off the wall.

However if the ceiling pitch is less, so is the drop. In my case 1 3/8:12 pitch (almost flat) even the minimum 3 1/2" protrusion is sufficient to meet the 18" horizontal setback.

I assume the tech people at Selkirk know this stuff. And they pointed out their standard adapter for flat ceilings to single wall pipe is only 3 1/2" and meets code fine.

Hopefully they are reading the code correctly. Unfortunately I don't have a copy (yet).

Anybody care to comment? This 18" number seems to be so strongly ingrained in peoples thinking that is strikes me as quite surprising that it could be wrong. But still, it's hard to argue with the logic.

 

[Corie]

THe 18" number comes from the horizontal distance allowed between a verticle run of pipe and a verticle combustible wall surface. Things change significantly when you're talking about clearence from the single wall to ceiling, in the case you're referring to. This is because almost all of the heat transfer from the pipe to the surroundings is in the form of radiation which leaves the hot surface in straight lines. Simply put, little radiation is heading out of the pipe directly parallel to the pipe direction, so different clearences apply.

 

[Highbeam]

Then this "reference" calls out 4" as the minimum chimney protrusion for flat ceilings but gives proper notice that sloped ceilings must meet the perpendicular clearance for the type of connector pipe.

(broken link removed to http://www.chimneysweeponline.com/hochim.htm)

 

[sbedelman]

THe 18" number comes from the horizontal distance allowed between a verticle run of pipe and a verticle combustible wall surface. Things change significantly when you're talking about clearence from the single wall to ceiling, in the case you're referring to. This is because almost all of the heat transfer from the pipe to the surroundings is in the form of radiation which leaves the hot surface in straight lines. Simply put, little radiation is heading out of the pipe directly parallel to the pipe direction, so different clearences apply.

Right. I agree. That was my logic but until I reached this person at Selkirk every person insisted that the minimum clearance parallel to the piple was 18". In fact the link supplied by one of the posters says 18" in all directions. Selkirk says this is flat out wrong.

Assuming Selkirk is right (and I now believe they are) I am surprised how much misinformation there is out there on this topic. Selkirk says it is clearly stated that the 18" measurement is only to be taken perpendicular to the direction of pipe but not one web site makes even a mention of this fact.

Our installer insisted we needed 18". I'll bet the inspector will do the same (stay tuned). We are obviously going to discuss the matter prior to installation and resolve the matter then not after the fact, but to do so I want to be on absolutely firm ground. The amount of (apparently) misinformation circulating is going to make this more difficult. I mean as of today I have one person at Selkirk against more or less the whole world.

Yikes.

 

[Corie]

Well I'm on your side too! haha

Whenever I install pipe in the situation like you're talking about, I always extend it four inches into the room. I've read that in almost every chimney manufacturers instruction manual.

 

[sbedelman]

Well I'm on your side too! haha

Whenever I install pipe in the situation like you're talking about, I always extend it four inches into the room. I've read that in almost every chimney manufacturers instruction manual.

Yeah the Selkirk manual S1 alludes to this, but it isn't all that clear and probably not clear enough to sway an inspector who comes in with a strong notion that it is otherwise.

It has been extremely helpful to get confirmation of Selkirk interpretation. And will make for a much cleaners installation.

Thanks to everyone for the help.

 

[Gooserider]

Well I'm on your side too! haha

Whenever I install pipe in the situation like you're talking about, I always extend it four inches into the room. I've read that in almost every chimney manufacturers instruction manual.

Yeah the Selkirk manual S1 alludes to this, but it isn't all that clear and probably not clear enough to sway an inspector who comes in with a strong notion that it is otherwise.

It has been extremely helpful to get confirmation of Selkirk interpretation. And will make for a much cleaners installation.

Thanks to everyone for the help.

I would try to get Selkirk to give you something in writing (with an engineer's signature) to back up what is in their manual - that would hopefully carry some weight with the intaller and inspector to say that this what the mfgr of the chimney specified as appropriate.

Gooserider