Convection loop in chimney?

[Ehouse]

A lot of posts seem to be asking about overfire and/or air control problems. Is it possible for a convection loop to form in a chimney under certain conditions? I'm going from a 4" smoke pipe to a 6" class A chimney. I'm wondering if the relatively small column of heated air rising upon start up or even during normal usage can allow cold air to drop or be pulled down to the combustion chamber. This would seem to be a way for air to flood the stove, even with everything shut down, causing the stove to take off. Would this be an argument in favor of a stovepipe damper? Sorry if this has been covered before. I haven't read very far back in the posts.

Ehouse

 

[tfdchief]

I have never heard of anything like that before.

 

[begreen]

4" flue pipe? What stove is this?

 

[oldspark]

Sounds like a camp stove.

 

[pen]

I've never found a downdraft being created, after I stuck a match to the load in the stove. If I have a downdraft that I need to correct, I can tell the moment that I open the door on a cold stove. Either it is there or not. If it could make a switch because of the heat as you mention, I'd have to guess that it is rare.

Now, next to a liner in a masonry chimney there most certainly would be a convection loop if it is not insulated.

W/ a modern stove a damper is not necessary, and should not be used unless you have an overdraft condition (excessively tall chimney) since modern stoves are very dependent upon draft to run as they were designed. I have a damper on my chimney but I've only used it 2-3 times during extremely cold / windy spells as the stove was starting to take off on me. The Mrs., who refers to the flu damper as an "emergency brake" uses it more often than me just to slow thing down if she lets it get a bit too hot on a reload.

pen

 

[Ehouse]

After thinking about it, I don't think the pipe diameter is a factor in my case because the smaller dia. pipe would restrict any back draft. I don't really have a severe problem with my stove (1984 Weso german tile stove) although it likes to burn hot ( cruises at around 750*). I brought this up because there seems to be a lot of mystery overfireing out there. I was reading about convection loops in hydronic pipes causing problems where the hot and cold water separate in the pipe and circulate creating havoc with controls. I wondered if this scenario could arise and contribute to problems in chimneys.

Ehouse

 

[pen]

Maybe in a very large chimney w/ an open fireplace? Not saying it can't happen, I've just never heard of it w/ a standard system.

pen

 

[oldspark]

"I brought this up because there seems to be a lot of mystery overfireing out there"
I think the only mystery out there is to the person unfamilar with their setup, I bet that is a neat little stove, any pictures?

 

[Backwoods Savage]

After thinking about it, I don't think the pipe diameter is a factor in my case because the smaller dia. pipe would restrict any back draft. I don't really have a severe problem with my stove (1984 Weso german tile stove) although it likes to burn hot ( cruises at around 750*). I brought this up because there seems to be a lot of mystery overfireing out there. I was reading about convection loops in hydronic pipes causing problems where the hot and cold water separate in the pipe and circulate creating havoc with controls. I wondered if this scenario could arise and contribute to problems in chimneys.

Ehouse

If this is true you have a 4" going into a 6" then there can be some big problems with draft. That 6" is just so darned much larger than the 4" that you can lose draft. This is why your flue needs to be the same size as the stove.

Is this perhaps a pellet burner you have?

 

[Backwoods Savage]

Ehouse, you could help yourself and others if you would put the make of your stove into your signature line. Just go to "Your Control Panel" at the top of the page and you can edit the signature line there. This way it will always show up whenever you post.

 

[Ehouse]

I have good draft with approx. 23' of chimney. It seems to draw very well. I ran this in a post back in Sept. before my install and BeGreen replied saying it shouldn't cause any problems if it wasn't too long a run of 4". I might experiment with some 6" pipe after the holidays to see if it makes a difference, but I'm happy with it as is for now. I updated my sig.. Should show up when I post this thanx for the heads up.

Ehouse

 

[Backwoods Savage]

Good. I hope the 6" works out. Let us know how it does.