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I'm installing a wood stove. The regulations say that the chimney top should be at least 2 feet higher than any part of the roof within 10 feet horizontally . . . from what I've read, this seems to be all about draft. And it's also a bit unclear as to what the nearest part of the roof means. For instance, my house has a second story but the part of the roof that the chimney penetrates isn't a second story; in other words, the chimney goes through a first floor roof, but where it emerges, it's about 8 or 9 feet over to a second story external ( steel sided wall ).

So, if the chimney needs to go higher than that wall, it would be like 12 feet high, which seems unreasonable. But, if it's only about draft, I imagine the constraint is based upon the roof that the chimney comes from. So that it's not interrupting air flow.

Can anyone provide clarification?

Martin
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chad
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2 Answers2

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It means what it says. If you go 10 feet from the chimney in any direction horizontally, you need to be at least 2 feet above the roof. Which means that your chimney is poorly located, if it's within 10 feet of a higher roof. So it needs to be 12 feet tall, if that's what it takes. Wind currents over that higher roof can cause downdrafts in the chimney - and that sort of thing is precisely what the language is there to prevent.

Depending how far along your install is, you could potentially move the chimney so it's more than 10 feet from the second story.

Ecnerwal
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  • Wind breaking over the comb of a higher roof makes for really interesting "Fist of God" downdrafts due to the aerodynamics. The type that completely reverse the flow in the flue and push it out of every orifice in the pipe joints and stove casing. It's even worse if you have an open fireplace as there's no recourse to keep the smoke out of the living space. You want the top of the chimney out of that downwards airflow. – Fiasco Labs Dec 17 '13 at 04:56
  • Wood burning stoves can also produce poisonous but odorless and colorless [carbon monoxide](http://www.thecompliancecenter.com/blog/2011/10/12/carbon-monoxide-protection-with-woodstoves/), I wouldn't want the possibility (however remote) of carbon monoxide being blown back into my home by a back-draft. – RedGrittyBrick Dec 17 '13 at 15:38
  • Is it feasible to have a 12' high chimney, from a stability point of view? – chad Dec 17 '13 at 16:20
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    You need to brace it, and it's inconvenient to clean, at best (make sure you can get a cleaning rod in from the bottom.) Most of the stock braces for metal chimney are made for holding it a smaller distance away from a wall (between 1-3 feet) so supporting it 8-9 feet out will be a project. A masonry chimney CAN be built to be stable for that sort of distance on its own, but it takes planning and skill. – Ecnerwal Dec 17 '13 at 16:35
  • So, isn't a very tall chimney going to reduce draft as well, by virtue of it's cooling effect on the gasses. So, since I'm only 1.5-2 feet from being outside the 10 foot clearance, couldn't I do an elbow or something after coming through the roof -- to jog away from the other structure enough to gain the 10' ? This would impact draft as well, but perhaps not much more than the tall chimney. Plus, my system is totally straight up to the roof, so it's pretty ideal draft to start with. – chad Dec 18 '13 at 16:33
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    A tall chimney actually improves draft. – Ecnerwal Dec 18 '13 at 17:33
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In Ontario, at least, it doesn't even need to be your roof.

This article (and the following week's, 2009-12-26):

http://aaron.ca/columns/2009-12-19.htm

details how renovations to House A, carried out with all necessary permits, intruded into the clearance space of a chimney of neighboring House B. Result: House B had to rebuild its own chimney at its own expense, or have their gas turned off.

DJohnM
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  • Not sure this is an answer . . . but very interesting :) I was just in Toronto for the first time a couple months back; beautiful city. – chad Dec 19 '13 at 22:37