Routing a chimney around a window?

[Badfish740]

I'm faced with a little dilemma in where to place my add-on furnace. I have a ready made opening in my foundation wall in the form of a window that I intend to gut (remove window/all wood framing) and install a thimble/outside air vent in as it is nearly 20" high x 36" wide and will provide plenty of space. The other advantage of course is the simple fact that I don't have to put another hole in my foundation wall. The dilemma is that centered directly above this window is a first floor window. In order to run the chimney out of the existing basement opening I would need to run the chimney around the 1st floor window which I should be able to do via two 30 degree elbows and a short section of pipe. I've enclosed a crude diagram of what it will look like. Is this normally done with Class A? Will I have enough draft? Total bends in the system will be a 90 from the stove to transition out of the window, the tee (90) to route the chimney up the side of the house, and the two 30s. The straight run of pipe after that would be 15' but I could always add more. Finally, what would I need to do in order to support something like this? I would think that the normal tee brace at the base of most chimneys wouldn't be that effective by itself since the load is not centered. Should I just use wall bands every 4 feet instead of every eight with an additional one at each 30 degree elbow?

 

[Patapsco Mike]

I did EXACTLY what you just drew at my last house. Triple wall out the basement casement window, two 30's to not block an upstairs window. I had a 24' run (total) from my basement to above the roofline of my Cape Cod.

I did have some modest draft issues, probably as much the result of being in the basement as it was due to the two extra 30's. But it worked fine, and heated my house very well for 5 years using a VC large Dutchwest (cat).

I used wall bands just like you described at each 30, but only every 6 feet going up the side of my house. Then of course you need the brace kit with adjustable arms for the part that extends above the roof.

The worst part of this kind of set up is that you don't have room below the clean-out for cleaning the flue. Not that big a deal, just have to take out the single wall part inside the house, clean as usual from outside the house, then suck it out (from outside the house) with a shop-vac.

Another issue is clearance to your ceiling in the basement. Most casement windows exit very close to the floor joists. Mine was very, very close. I had to use a combination of heat shields and special heat tolerant drop-ceiling tiles to get it to work safely.

When I moved out of the house, it was very simple to remove everything. Didn't leave a mark except for a few screw holes in the siding.

You don't need to worry too much about support, the two 30's and the bands would support the whole thing even if no T was there (provided they are anchored correctly to the house).

 

[Badfish740]

I did EXACTLY what you just drew at my last house. Triple wall out the basement casement window, two 30's to not block an upstairs window. I had a 24' run (total) from my basement to above the roofline of my Cape Cod.

I did have some modest draft issues, probably as much the result of being in the basement as it was due to the two extra 30's. But it worked fine, and heated my house very well for 5 years using a VC large Dutchwest (cat).

I used wall bands just like you described at each 30, but only every 6 feet going up the side of my house. Then of course you need the brace kit with adjustable arms for the part that extends above the roof.

The worst part of this kind of set up is that you don't have room below the clean-out for cleaning the flue. Not that big a deal, just have to take out the single wall part inside the house, clean as usual from outside the house, then suck it out (from outside the house) with a shop-vac.

Another issue is clearance to your ceiling in the basement. Most casement windows exit very close to the floor joists. Mine was very, very close. I had to use a combination of heat shields and special heat tolerant drop-ceiling tiles to get it to work safely.

When I moved out of the house, it was very simple to remove everything. Didn't leave a mark except for a few screw holes in the siding.

You don't need to worry too much about support, the two 30's and the bands would support the whole thing even if no T was there (provided they are anchored correctly to the house).

Thanks! That's exactly what I was looking for! As for exiting the house through the window it will be tricky, but I should be able to mount the thimble low enough in the opening so as to allow for enough clearance using double wall stove pipe. As a precaution however, I'm still going to shield the floor with a 1" air gap and hardi-board.

 

[Patapsco Mike]

What I did to get through my house was use a through-wall thimble custom cut to fit right into the old steel frame of the window casing. My windows were steel framed and divided into two panes. I had the stovepipe thimble replace one pane, and the other pane was still glass. I liked this because I could look right through it to keep an eye on they exterior and also because it leaked cold air which constantly washed over the hottest part of the junction (and probably helped improve my draft). The window frame was cut into solid cinderblock so there was great support.