How should I do a pass through this wall?

[Dajolu]

I would like to put a Morso 3440 stove in a man cave project I am working on. How can I pass the stove pipe between these studs? Is there a specific thimble I need to use? Or should I re-frame it? Also. What insulation should I put in? I plane to put durock and tile the back corner and the stove will easily meet clearance to combustibles.

 

[begreen]

The chimney pipe manufacturer usually has a thimble that ensures proper clearance for the short section that comes off of the tee to pass through the wall. Here is a picture of DuraTech's.

The other, much better option is to go straight up through the roof. This also may be a less expensive option. Beside drafting better by eliminating the 90º turns in a short flue path, it also requires less fittings.

Chimney info Thread 'CHIMNEY - PASSING A CHIMNEY THROUGH THE WALL'

Oct 17, 2015

DON’T Just “Do it” - Placing a wood stove into an existing masonry chimney could be hazardous to your health and house. Read this to learn more.

One of our biggest problems occurs when a customer enters the shop and states “I have an existing woodstove into a masonry chimney - I’d like to replace the stove with a more modern one”.

In the old days, we thought this was a gravy job…these days I wonder if I should send them packing….why? because:

1. 90%+ or more of existing masonry wall-pass throughs are wrong

2. It is often difficult confirming or repairing these...

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[Dajolu]

The chimney pipe manufacturer usually has a thimble that ensures proper clearance for the short section that comes off of the tee to pass through the wall. Here is a picture of DuraTech's.

The other, much better option is to go straight up through the roof. This also may be a less expensive option. Beside drafting better by eliminating the 90º turns in a short flue path, it also requires less fittings.

Going up through the Ceiling is not feasible for what is above that corner. So I would make a hole in the block and tile to accommodate that thimble and there would be enough clearance with it being centered between the two studs?

 

[Dajolu]

The studs are non load bearing, I am wondering If I should frame it out around where the thimble will go for extra clearance.

 

[begreen]

The thimble should fit between the studs if they are 16" OC. It will maintain the proper clearance for 6" class A chimney pipe passing through the wall if it is not triple wall pipe (not recommended). DuraTech or Selkirk Ultratemp are examples of double-wall class A chimney pipes.

Note that for secondary combustion the stove needs sufficient draft. They are typically tested on 15' flue systems straight up. That can be harder to achieve in a small cabin. Each 90º turns is like reducing the height of the flue about 2ft so 2 90º turns is like lopping off 4ft of chimney. This can lead to disappointing burns.

At the least, soften the inside 90º turn by using 45s and an offset.

 

[Dajolu]

Thank You, There is a second story above this area so I think there will be at least 16' from the stove top to the top of the roof. Probably more with the stove pipe going through the roof gable and clearing the peak. I have to measure later to get a better idea of chimney length. I am not opposed to two 45 elbows also.

 

[begreen]

Got it, I mistakenly thought this was a small independent building.

 

[Dajolu]

Its ok, its a weird space built into a hallow so its partially built in ground and the rest outside with a small garage like building on top. Thank you for your help.

 

[Dajolu]

Can that wall thimble be attached to the cement board and then tiled over so that only the circle is visible?

 

[begreen]

Can that wall thimble be attached to the cement board and then tiled over so that only the circle is visible?

The interior trim piece is not flush, it has a rim of about 1/4" or so. This would raise the surface of the cement board if it covers it but maybe that lip could be cut off?? Call the chimney manufacturer's tech support and ask. BTW, that is just one brand example. There are several different brands of good chimney pipe. Selkirk uses a flat round plate for example to trim out their thimble.

 

[Dajolu]

Ok thanks for all in info, one more question (for now..) the exterior of the block is decorative and uneven. the exterior thimble plate will not sit flush, also I would have to cut a very large hole in the cinderblock to fit the thimble. Can I cut an 8" hole and pass the chimney pipe through the block and then have the thimble in the inside to meet the clearances for the studs?

 

[begreen]

The thimble is a two part assembly. This keeps the pipe shielded and in alignment. The diagram makes it look like the outside collar would be between the existing studs and the masonry. How would that trick be pulled off?

Is there sheathing or substrate between the masonry and the studs? If so, what is it, cement board or plywood?

Theoretically, as long as the inside half of the thimble 100% shields the wood studs by providing at least 2" clearance and stays centered on the pipe, then just using the inner collar may work, especially if it penetrates the masonry a little bit. First, one needs to establish the length of the inside collar is at least long enough to do this (4.5"? If there is plywood or chipboard sheathing then more.) The exterior hole should be 8.25" to allow for this and to facilitate ease of installation. Caulk the 1/8" gap outside with a good quality, non-acid, silicone adhesive like GE Silicone II afterward.

 

[Dajolu]

The thimble is a two part assembly. This keeps the pipe shielded and in alignment. The diagram makes it look like the outside collar would be between the existing studs and the masonry. How would that trick be pulled off?

That would be a bit of a trick wouldn't it. There may be a small gap between the studs and masonry. but probably not enough to squeeze the outside collar. No sheathing or substrate between the studs and masonry. I could chisel a circle or make a circle with small drill bit holes into the masonry to partially fit the inside collar and make an 8.25" hole the rest of the way for the chimney pipe. I will order a thimble and play around with it and post some photos to make sure it looks safe.

Thanks again for clearing this up.

 

[begreen]

If renting or contracting a concrete hole cutter machine to cut the 8" hole is an option, I'd go that way.