How to Increase Chimney Draft

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BPatrick
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Post Mon. Dec. 16, 2013 4:16 pm

I was reading the thread, overdraft and I read a couple of posts regarding low draft. One member, CC, said that for every 1 overdraft, there's 10 under-drafts. What things can you do to increase chimney draft. Someone mentioned caps; does the adjustment of the cap effect chimney draft. What other things would increase chimney draft. I have good draft in an old house but may remodel an attic and the concern with the height would be low draft. I can't be the only person on here wondering about low draft. I would find this very educational. I actually copy and paste some of the really great threads as there is technical information on here that's really helpful. I thank everyone, in advance, for the comments.

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Post Mon. Dec. 16, 2013 4:37 pm

i have used this style of cap in three diff. installations and they really do increase draft by a sig. amount.

http://www.famcomfg.com/chimney-caps-1/wind-direc ... nized.html

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Rob R.
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Post Mon. Dec. 16, 2013 4:42 pm

Generally speaking, I think most chimney caps either do nothing to improve draft or slightly reduce it. If you want to increase the draft, you either need to raise the height of the chimney or increase the temperature of the gasses going up through it.

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Post Mon. Dec. 16, 2013 6:37 pm

Rob R. wrote:Generally speaking, I think most chimney caps either do nothing to improve draft or slightly reduce it. If you want to increase the draft, you either need to raise the height of the chimney or increase the temperature of the gasses going up through it.
Yup Thats the big and small of it.

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Post Mon. Dec. 16, 2013 6:44 pm

What rob said is spot on.

wind directional caps do increase draft - when there's wind, and, as long as they don't seize up. Other caps do nothing or often decrease it - especially caps with screens.

The proper way to increase draft on a chimney is to extend its height; you can dump extra heat up the flue, but, then you're wasting heat to accomplish what a few more feet of height would get you all the time- more draft.

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Post Mon. Dec. 16, 2013 6:52 pm

If you can insulate a chimney and keep it from losing the heat of the exhaust going through it you can help your cause. On an exterior masonry chimney adding a layer of foam and Dryvit over it you would be amazed how much better they draw and don't accumulate creosote(if yer one of those w#$d burners) It would be the same principal as building your chimney up the center of the house.

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Post Tue. Dec. 17, 2013 10:10 am

Thanks for the information. Waldo, building the chimney in the middle of the room is like insulating it correct? Berlin, adding a few more feet really makes that much difference? The chimney would be at the highest point of the house, but still adding height to it would still increase draft?

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Post Tue. Dec. 17, 2013 10:21 am

I think being at the highest point it will be easy to have good draft with minimal chimney. It's where the house wants to draft naturally.

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Post Tue. Dec. 17, 2013 10:23 am

My chimney does go up through the center of the house. This year I replaced the old stainless liner that I'd used with the woodstoves for 25 years with an insulated multiply ply liner rated for coal (316ti). I've gone from an "ok" draft that was fine as long as I left the chimney cap off to too much draft with the cap installed even with the MPD closed. Waiting for a thaw so I can get up on the roof & reduce the height of the cap over the liner outlet an inch or so.

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Post Tue. Dec. 17, 2013 10:33 am

JohnB wrote:My chimney does go up through the center of the house. This year I replaced the old stainless liner that I'd used with the woodstoves for 25 years with an insulated multiply ply liner rated for coal (316ti). I've gone from an "ok" draft that was fine as long as I left the chimney cap off to too much draft with the cap installed even with the MPD closed. Waiting for a thaw so I can get up on the roof & reduce the height of the cap over the liner outlet an inch or so.
yep know the feeling. I have a smooth wall 316 liner and have enough draft to bale up and sell :lol:

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Post Tue. Dec. 17, 2013 11:19 am

franco b wrote:I think being at the highest point it will be easy to have good draft with minimal chimney. It's where the house wants to draft naturally.
Bingo on this. Stack effect of the house should promote draft with a short chimney if the stove is on an upper level.
Last edited by Lightning on Tue. Dec. 17, 2013 1:06 pm, edited 1 time in total.

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Post Tue. Dec. 17, 2013 12:46 pm

i just had alighting storm in my head :shock:

i have a center of the house brick chimney with a smooth wall 316 liner, total vert. height is 23Ft. from the top of the stove collar.

there is also 2, 90* elbows AND a clean out "T" in there and I seem to remember that 90's where considered to be equal to 10Ft. of straight pipe.

does that mean that my chimney is 53Ft. functionally ? if so I think i'll go to 2, 45's and cut 10Ft. off of it.

or i'm crazy and will just be spinning my wheels.

any way, if this is true, could a guy add a couple 90's to his stove pipe gaining functional height and draft ?

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Post Tue. Dec. 17, 2013 12:53 pm

90 degree bends are restrictive. Each one you add will make the chimney behave as if it was shorter.

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Post Tue. Dec. 17, 2013 12:55 pm

I think the 90's are subtracted from the height. They recommend as few 90's as possible as to NOT impede flow. Adding them would make a poorly drafting chimney worse.

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Post Tue. Dec. 17, 2013 12:56 pm

Rob types faster than me! :)

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