How Does Chimney Height Help or Hurt Burn Performance

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jscs.moore

jscs.moore

Feeling the Heat
Sep 9, 2015
291
Eastern PA
Hey Guys...I had a Hampton HI300 installed recently and will be doing my first/break-in burn this weekend. I have a 6" ovalized, double walled, SS, pre-insulated liner (Olympia) and my chimney is 35ft. I've gotten great info off of this site and have read some stuff about chimney height and draft that has left me a little confused. So is a tall chimney better or worse than a short chimney for burning? What are the pros and cons? I hope you don't tell me a 35ft chimney is bad, because there isn't a damn thing I can do about that! This is an awesome site, but can be overwhelming for a newbie.
 
A tall chimney is better than a short chimney. However, too tall of a chimney can cause exceptionally strong draft which can reduce burn times, and cause some stove parts(cat) to clog sooner(this is largely dependent on the individual stove though).

35ft is on the really tall side. My chimney is about 28ft, and that's usually considered pretty tall
 
Usually people get in trouble because their chimney is too short, not because it is too tall.
 
What those guys said . . .

Some folks with taller chimneys find that a damper can be useful if they are getting too strong of a draft which is causing the fire to get a little too hairy for comfort . . .
 
35ft. is very tall. Some stove companies put a caveat in their documentation about too tall chimneys. Too strong draft can make the stove hard to regulate. It is designed to work within specific draft parameters. Draft can be measured and if needed it can be reduced by introducing a damper in the flue pipe and possibly by reducing the pipe size just under the chimney cap. In some cases the stove air intakes may also need to be reduced to compensate.

If the stove is in a basement installation then the system may balance out a bit due to the tendency for pressure in the basement to go negative. Again, this can be measured.
 
Thanks for the feedback...I think I may have jumped the gun on the chimney height. I have a 2 story Center Hall Colonial, I assumed it was a 35ft chimney because the install work order said 6"x35' Flex-Inset Kit for the liner. But don't they order extra length to work with when installing? The chimney top is about 4 to 5 ft above the roof line...so I'm thinking on a 2 story house that would not be 35ft tall?
 
Depends on the attic height and chimney penetration location. It could be closer to 32ft but hopefully they aren't putting a 35' liner in a 25' chimney. That would be an expensive waste.

PS: I misread and thought this was the freestanding Hampton. Now I see this is an HI300 and not an H300. A stove pipe damper is not an option in a flue liner.
 
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When I moved in to my house 18 yrs ago the fireplace had a Damper in the fireplace and a Spring Loaded Damper at the very top, With a chain that hung down in the fireplace. The chimney sweep guy told me between the two the one at the top controlled it better ( this was an open fireplace, Before the wood stove) Can he do that??
 
I don't think so, with an insert, how would one access the chain controlling the damper? Even in a fireplace I would be leery of this practice. If the chain is hot and slips in one's hand and closes off the damper the house would immediately start filling with smoke. Gloves may not be close by to remedy that situation.
 
I also have a 25+ foot chimney with an HI-300. I always felt like the fire was a little difficult to control, and I always had to burn with the damper closed 80-100%. I did two things to address this.

1. I did the dollar bill test after about 2 or 3 years and found the door gasket seal wasn't very tight. That was fixed by adjusting the door latch. There are some washers in there that you can remove to tighten up the door a bit if necessary. Procedure is in the manual. Shouldn't be necessary for a brand-new unit, but it's easy to check.

2. I plugged what I thought was the auxiliary air supply hole with some aluminum foil (wadded into a ball and pressed into the hole). In retrospect I am not sure the hole I plugged was actually the auxiliary air. It might just be a cutout to allow the air control rod to be switched from the left to the right side. So maybe this "change" didn't have an effect. https://www.hearth.com/talk/threads/hampton-hi-300-auxiliary-air-hole.132827/

Nevertheless, with these changes, the unit seems to be significantly more controllable. Now I run at more like 50-90% closed on the air control rod, and if I close it 100% it kills the fire quickly. This is the behavior I wanted.

-Jim
p.s. here is a really interesting thread from a guy who modded the HI300 to incorporate a feedback-control system for the burn. http://inveninc.com/SmartStoveForum/index.php?topic=19.0
 
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I'm new to this conversation, but learned a lot from BeGreen and others - thanks!

I too will be purchasing / installing a zero-clearance fireplace (leaning towards the Heat and Glo Northstar) in a 'bump-out' configuration. My specifics are similar to the original post - I will have 30-35 feet of chimney pipe (Duravent DuraPlus triple wall) straight up the outside of the house and like the original poster, I can't change this layout - blah! I'm rather concerned about 'cold backdrafting' as the attached article (link below) talks super negatively about my high outside chimney scenario.

http://www.woodheat.org/outside-chimney.html

Is there anything I can do to help alleviate backdrafting such as dampers, etc?

Your help / input is greatly appreciated - thanks in advance!

Matt
 
i have a basic colonial and with it on the first floor its 27 ft to the top! so if it was to be in the basement it would be about 35 ft
 
Depending on the stove insert and the size of the fireplace I would think that it would be possible, if there is room for a short section of pipe above the stove (6" tall?), to install a damper in the flue. You would need to drill a hole in the surround and then fabricate and install a rod or some sort of linkage through the hole that attaches to the damper handle. Might not be possible for everybody, but for some I'd think that would work
 
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