Any comments on my chimney setup?

Hi all,

I've been meaning to ask about my chimney setup, so here goes.

Last fall I removed the old 7" interior diameter insulated chimney. It was older and the walls were 1" thick, what is referred to as "Class A chimney" up here in Canada - a style that is no longer acceptable for wood burning applications. There were two 3' sections for a total of 6', with half in the (crawl in) attic and half outside the building envelope.

The new chimney I've installed is modern Selkirk-Metalsbestos 6" ID (stove didn't require 7") and I replicated the old setup's two 3' sections for a total of 6' of chimney. However the new ceiling support protrudes further into the room than the old one did (check out my avatar to see what the old ceiling support looked like - that single wall was about 2" from the very combustible pine ceiling), so I suspect the chimney height vis-a-vis the roof peak is no longer adequate (if it ever was) and I plan on adding a 1' section.

The stovepipe is about 5' and completely vertical.

So my questions are:

Will another 1' of chimney improve the draft much?

Could the chimney be too cold? There's only about 6" of chimney in a heated part of the cabin. The attic may be sheltered compared to outside, but it's still freezing in the depths of winter.

Do these manufactured chimneys fail often? I'm pretty confident of the installation, clearances, framing, etc, but I have to say that the way those sections are connected to each other and the ceiling support doesn't inspire a lot of confidence.

Is it possible/advisable to build a sort of internal chase around the chimney in the unheated attic - let's say with Durock and other non-combustibles? Would there be any reason not to do this? I'm thinking even if it wasn't completely sealed it would keep the chimney warmer and perhaps offer a small measure of safety in the event of chimney failure. Also, it might stay warm enough to allow a smoke detector to be installed inside. As I understand it most/all smoke detectors need to be in an environment that is at least 40 degrees F or 4 celsius.

Matt,

Need more info - You never actually stated, do you have a draft problem or you are just wanting to improve it? What stove are you burning, did you have draft issues with the old chimney?

One foot can make a big difference if it gets you over the 10/2/3 rule reguarding chimney hight. You have to get above the roof line 2 feet to prevent eddies of wind ripping down your chimney.

It can get to cold and condensate creating cresote problems, the only fix there is a insulated chase. This issue is more common in cold climates.

I think insulating the attic portion would be a waste of time realy, thats my take anyway.

There's currently an old Jotul 118, I'll be installing something smaller and modern before the fall. The draft is reasonably good but it does spill a bit of smoke when opening the door sometimes, I've heard that was one a problem with those old Jotul 118s.

The old setup (7" chimney, 6" stovepipe) drafted tolerably well, but it was different in 2 respects: the stove's big baffle wasn't installed, so it was working as a box stove, and the stovepipe wasn't a straight shot, it had a couple of bends in it.

The 10-2-3 rule - I know the 10-2 part of it... the 3 part means there has to be at least 3 feet exposed? I suspect it might be 6-12" too short.

Draft problems are rarley caused by a stove, there almost always casued by the chimney or negative pressure in the home. I dont think your 118 has anything to do with it. Add a few extra feet to the hight of the chimney and see if that helps. What altitdue do you live at? At my altitude nothing less then 18' works. the 10/2 rule is about preventing downdrafts from eddies, it doesnt have anything to do with haveing enought chimney to draft properly. It sounds like your chimney is a little on the short side. Yes, the 3 part of that rule is the minumum penetration.

Altitude is only about 1000 feet.

Am I the only one who worries about the part of my system that is within the building envelope yet cannot easily be monitored either by occupants (I have to get up on a counter, open the attic door and shine a light into the corner where the chimney runs) or by electronic devices (because they don't work at cold temperatures)?

I would say 14' is the minimum you would need to get strong draft. and of course be above the peak at least 2 feet, which you already stated that you might not be.

As long as you have an insulation shield and follow the CTC, you will be fine. How many feet of single wall do you have from your stove to the ceiling?

Reading threw the thread I come up witha couple suggestion some already made but to point out others.
Depending upon which stove you end up purchasing, the manufactures specs will tell you the miniun verticle length required to draft

Usually that verticle height is from the flue collar to the top exit The least I have seen speced is 12' the usual is 15'. Every change in direction (90 degree elbows) so mu ch friction is developed that 5' has to be added to the verticle height. For instance if 12 were the minium and you had one 90 degree elbow 17" verticle height would be required two 90's 22'. No connector pipe should have more that 2 90's. 45 degree elbow one should 2.5' additional feet

10/2/3 this is minium, The chimney shall pass 3' above any section of the roof if there is any part of the structure including, the roof domers, within 10" the totl height must be 2' higher than any part of the structure within 10' I have seen where the chimney exits the roof on the lower side not at the peak. If you tell me the pitch, I can tell you how high it should be. Just extending it 3' and having roof above it does not cut it, remember 3/2/10