Chimney Rules of Thumb

[Jeff Childers]

I am about to build a house with a stove and metal triple wall chimney that goes up through one side of a gable roof. What are the rules for clearances for the chimney? How far should it be from the roof surface and how far away from the roof ridge, measured horizontally, should it be to ensure good draft?

Thanks.

Jay

 

[JimWalshin845]

Jay,

I don't know the answer but tell people where you live. Codes are different between US and Canada.

Welcome aboard

 

[thechimneysweep]

Here's a sketch showing the minimum height for your chimney. Basically, your chimney must extend 3' above the roofing on the high side, and also 2' above anything within 10'. If the peak of the roof is within 10', your chimney must extend 2' above the peak.

Now, that's code minimum. Your question was about ensuring good draft, and I submit that nobody can tell you how to do that. The rule of thumb for woodstove venting is that the top of the chimney extend 13-15 feet above the firebox floor (the owner's manual of the stove you're installing may also specify a specific minimum height), but that doesn't always work. We start there, and add lengths of chimney if needed to establish good draft.

 

[Jeff Childers]

Thanks Jim and Tom. It was that 2-3-10 rule that I was looking for. I just couldn't remember it. Thanks for the drawing.

One more question: My house faces North and my chimney is on the South side of the roof. The chimney is more than 10' from the ridge line of the main house (which is 6' higher than my chimney), but it is only 6' from a closer ridge line which is also higher than the chimney. I can always just buy more triple wall pipe and extend the chimney's height, but does it matter that I may have 12' of bare chimney sticking up out of the roof? Should I take measures to protect or enclose the bare pipe? I am worried about convection drafts. Also, should I have a damper on this much pipe to keep my precious cool air from being sucked up the pipe in the summertime?

Jay

 

[thechimneysweep]

Hey Jay,

Your chimney must extend 2' over ANYTHING within 10'. If you have another ridge line within 10', it must extend 2' over that.

 

[Jeff Childers]

Hey Tom.

I can get compliant with the rule of thumb by adding pipe sections to the chimney. My concern is about having 12 feet of bare metal pipe sticking up out of my roof. Are there any issues with this sort of a situation? Should I build an enclosure around the pipe? I assume I must find a way to brace this stack against the wind, but is there anything else I need to be concerned about?

Jay

 

[thechimneysweep]

Chimney pipe is insulated, and I wouldn't be afraid of leaving it exposed. You will need a roof brace, though. Here's a picture of my house, showing 13' of exposed chimney and a custom roof brace.

 

[Jeff Childers]

Tom:

If you can do it, so can I. I'll just leave it exposed.

Thanks for the help.

Jay

 

[Rusty]

So what happens if you dont have your chimney by that rule of thumb, but you have a good draft?

 

[kieth4548]

I too have the same question. If there is anyone that can answer this please let me know. I am a new stove owner.

 

[RonB]

Ibjamn and keith,
My Quad installation book says the 2-10-3 Rule is for safety and is not meant to assure proper flue draft. The chimney must be the required height above the roof and any other nearby obstructions.

 

[kieth4548]

Ok.. thanks. I just installed my england stove last Friday and I was wondering about that same question. Looks like I will need at add an additional 12". Would that also cause some black stuff running down my roof. I got on the roof and noticed this and saw there was a little black liquid around the ring of the stove cap. I was a little puzzeled due to it being so new and it's already doing this. I had other people say this is normal.

Thanks
Kieth

 

[webbie]

Yes, the 2/10 rule is not for draft - it is more for safety - everything from making certain embers don't ignite the roof (especially cedar!) to making certain that gases and smoke do not turn downward and come into gable and roof vents.

So that is not a rule of thumb. It is required. That said, on certain roofs of ridiculous slope, some inspectors seem to let a couple inches here and there slide by.

An important part of this rule is "if any higher roof or part is within ten feet of the pipe, you must go higher than it".....

As far as actual chimney rules of thumb, we could start with as few 90 degree bends as possible, keeping much of the chimney interior, etc.

 

[JimWalshin845]

Would that also cause some black stuff running down my roof. I got on the roof and noticed this and saw there was a little black liquid around the ring of the stove cap. I was a little puzzeled due to it being so new and it's already doing this. I had other people say this is normal.
Thanks
Kieth

The black liquid, if it is gooey in nature, is probably creosote. Depending upon the stove you are operating, the wood you are burning and the environmental conditions it is not a huge concern unless it starts to get heavier and starts moving down the flue pipe. Check it weekly if possible and report back for possible solutions.

Safe burning!

 

[kieth4548]

thanks for the info.. I will get back if things get worse