chimney elbows

[ddug]

Due to design error (mine) on the house I am building I need to offset the vent pipe 2 or 3 feet to avoid some exposed rafter ties. When I purchased my chimney pipe I ordered two 45 degree elbow connections. While reading the installation manual I learned that they only make the elbows in 15 and 30 degree units, it is not permissible to join a 15 and a 30 to make a 45 degree bend. Fair enough, but somewhat confusing because I was holding their brand of 45 degree elbow in my hand.

I will buy some 30 degrees but am curious as to the reason for this limitation. Is it due to potential creosote buildup, or something else?

My main question is how to safely support this stack with the offset. There is a total of 16 ft. pipe from stove to ceiling. Do I need some kind of support bracket attached to the elbows? Do both elbows need support, or can I just do the bottom one?

Safety is the prime concern but I would like as clean looking install as I can manage. It is a cathedral ceiling and the entire vent pipe is exposed.

 

[LLigetfa]

Yes, it is due to the angle of repose WRT to creosote falling and collecting in the elbow. There should be no reason why the offset couldn't be achieved with smaller angles by the sounds of your situation so the smaller the better IMHO.

In my former home, I installed my stove in an alcove under a flight of stairs as a retrofit and the only way I could do it was with two 45 degree elbows. Five years later, when I built my current home, 45 degree elbows were no longer permitted but since I designed and built my own home, I could design around that limitation. I now have two 30 degree elbows to offset the chimney from the roof peak.

 

[LLigetfa]

As for your support question, I think the weight would need to be supported at the top elbow and the bottom elbow should be laterally supported. In my case, the chemney went through a ceiling and was chased through the second floor. The firestop provided lateral support and I supported the weight of the top section with four pipe hanger straps at the top elbow and by the bracket at the rafters.

 

[LLigetfa]

I am a little confused... Normally in an exposed installation, the chimney would start at the rafters and be supported by a cathedral ceiling support. There would then be single or double-wall inside smoke pipe running from the stove up to the cathedral ceiling support.

Are you running the chimney all the way down to the stove?

 

[ddug]

I am a little confused… Normally in an exposed installation, the chimney would start at the rafters and be supported by a cathedral ceiling support. There would then be single or double-wall inside smoke pipe running from the stove up to the cathedral ceiling support.

Are you running the chimney all the way down to the stove?

I'm a little new at this so I may get my terminology mixed up sometimes.

I have a metal support box attached to the rafters that 6 ft. of class A pipe connects to, 3 ft. below the roof and 3 ft. above. below the box there is 16 ft. of single wall pipe to the stove.

Do they sell special brackets to support the pipe/elbows?

 

[SteveKG]

The Selkirk [Metalbestos] angles [elbows] come with support bands and straps. I don't know about other brands.

 

[LLigetfa]

OK, sorry about my poor reading comprehension. Single wall smoke pipe is usually held together by screws and self supporting if vertical but may at times be supported by piano/picture/rebar/#9 wire if run off from vertical. If run near enough to a wall or other structure, long L brackets may be used.

How long will the run be from the top elbow to the cathedral ceiling support? I might suggest four wires from the four corners of the cathedral ceiling support to the top elbow.
How long will the run be from the stove to the bottom elbow?
How long will the run be between the two elbows?
How far away will any of it be from the structure?

 

[ddug]

The stove will be directly underneath a rafter tie beam, the beam being about 11 feet above the floor. I need to move the pipe over almost 3 ft. so if I use 30 degree elbows that would take about 4 ft. of pipe to move it over that far. I have some leeway as to where to place the bend but it will be more or less in the middle of the 16 ft. run. The bottom elbow would be almost directly under the beam so I could support that one from there pretty easily.

I thought maybe if I had the lower one anchored down good the top elbow may not need support? The stove is near the center of the house and the pipe is not near any walls.

Thanks for the help.