Gaps around chimney cap reducing efficiency?

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New Member
May 7, 2017
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Hey guys

Ive a question about how to get the most out of my inglenook’ed Jotul F3.

First, some housekeeping. Have a moisture meter, all wood is dry (15% or lower), Australian hardwood, no smell of smoke, CO2 alarm set up.

When the stove was first installed, we didn’t put a flue cap on the top of the masonry stack and the fire was very inefficient. We only ran a metal flu pipe half way up. (I think you call the pipe a “chimney liner” in the states).

Now, an installer has improved our stove and the flu is all the way to the top and there’s a cap. See the first photo below. The fire is much more efficient.

But can it be better? There are gaps where the plate and cap were installed. If I look up through chimney during the day, there is light coming through both the gap between the pipe and metal plate, and between the plate and masonry. See the second picture.

Is it worth sealing these gaps? Surely hot air would be flowing out of them. If so, what product is the best to use? I want something fire safe that can be removed if we ever want to move the stove.

Thanks for any tips or advice.

Usually a thick bead of silicone is run around the top of the chimney before the top plate is put down. Any good silicone will work. I've used GE Silicone II with good results.

PS: What is the height code for chimneys there? It doesn't look like it meets the 10-3-2 rule.
10-3-2 rule.JPG
Thanks begreen. I’ll silicone around the plate and the flue liner with a heat tolerant silicone. Much appreciated.

Yep - the cap height is less than the highest point of the roof. It’s an old house, I imagine the codes weren’t in place when they built it. It’s odd that my installer didn’t mention it.
Regular silicone is fine. Just clean the area well and use a good quality silicone.