HELP!; Wood Stove out of control

"Backdraft" like in firefighting... gasses accumulating and not enough air to burn them off. The stove is gulping air back down the chimney and the combustible gasses are "exploding".

I'd almost err on the side of suggesting there is a long chimney on top of this stove that is actually overdrafting the stove. Gasses and wood won't burn in a vacuum... Typical chimney design height is about 15 feet or so in most stoves. That means the stove, if connected to a 30+ foot long chimney like the old-school VC insert that lives in my fireplace are going to tend to overfire real easily. It also leads to a situation where when wood is outgassing excessively like when you load the wood into it, you really can't close it up before it stops generating smoke out the chimney.

Closing up after a loading is a science. I usually load and let it burn with the bypass open until the wood is ignited all around it. Daylight hours, a peek at the top of the chimney tells alot too... steamy white smoke? Not time to close yet... little to no smoke? Close it up it's ready.

BeGreen said:

A complicating factor might be weak draft. This could be because of warmer outdoor temps, a fan on in the house or plugging. Have you checked the flue and cap for plugging?

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Same thing used to happen nearly every day in my wood boiler... old design New Yorker WC-90... burning wood, or coal in it at the time. Makes for some massive coal gas "WHOOSH!"es with the chimney and connector pipe chock full of coal gas and then the "ratio" finding the sweet spot and a source of combustion.

Solution there? I borrowed a draft gauge and checked it... "off the scale", so high it couldn't be read. Bought and installed a barometric draft damper and set it between .02 and .03 inches... per the owners' manual not more than .04 inches.

Rare occurrence now, with either wood or coal. The air supply to the boiler is sufficient to burn off the gasses because the chimney is not extinguishing the open flames before the gasses can burn off. The installer is "old school" and doesn't like BDDs on wood burners at all. He's right, "if there is a chimney fire"... but without the BDD the question is not "if" but when. It belched thick black smoke out of the chimney without the BDD. My neighbor asked if I was burning tires in it... With the BDD, it doesn't make much smoke at all with wood. On coal it makes NO smoke...

LeonMSPT said:

"Backdraft" like in firefighting... gasses accumulating and not enough air to burn them off. The stove is gulping air back down the chimney and the combustible gasses are "exploding".

I'd almost err on the side of suggesting there is a long chimney on top of this stove that is actually overdrafting the stove. Gasses and wood won't burn in a vacuum... Typical chimney design height is about 15 feet or so in most stoves. That means the stove, if connected to a 30+ foot long chimney like the old-school VC insert that lives in my fireplace are going to tend to overfire real easily. It also leads to a situation where when wood is outgassing excessively like when you load the wood into it, you really can't close it up before it stops generating smoke out the chimney.

Closing up after a loading is a science. I usually load and let it burn with the bypass open until the wood is ignited all around it. Daylight hours, a peek at the top of the chimney tells alot too... steamy white smoke? Not time to close yet... little to no smoke? Close it up it's ready.

BeGreen said:

A complicating factor might be weak draft. This could be because of warmer outdoor temps, a fan on in the house or plugging. Have you checked the flue and cap for plugging?

Click to expand...

Click to expand...

Well, in our case it was a short, exterior, uninsulated, masonry chimney. Exactly the recipe for NOT having overdrafting. Yet, we still had a completely unsolvable backpuffing issue with the old VC.

Well, even a broken watch is right twice a day. The old VC insert I have is a non-cat. The problem I was having was runaway conditions. It's old and getting a little loose. I resealed the seams and replaced door and glass gaskets, and fixed a pretty significant air leak a couple years ago. Then it REALLY took off, and I was lucky I didn't damage it. When it was apart while working on it, I noticed the secondary air supply ports in the bottom in the very back. Looked like too much air to me, so I throttled them back a little. A little too much, thing didn't work for a hill of beans. Took it apart and gave it half again as much air. Real good after that.

Frankly, I am not completely sure on resolving your issues. Might make sure your chimney is clean and try open the cleanout about halfway and see how the thing works with less draft. It will answer the question... just be sure it's closed "enough"... if smoke comes back out the door of the stove when you open it, there's not enough draft. My initial suspicion is there's going to be PLENTY even with the cleanout open.

How large is the liner inside the chimney? Six, eight, inches?

****
You are correct; there is a long chimney; it is two stories plus, probably around 30 feet. As I mentioned, I have absolutely no problem starting the stove and reaching high temperatures quickly. The stove runs great without the CAT engaged. Once the damper is closed and the CAT engaged, things often go awry. Same thing happened last night: I lit it up and ran it for almost an hour and a half before engaging the CAT, so there was a nice bed of coals. I turned down the air supply for a while before adding wood, then let it run for about 10 minutes with the added wood before engaging the CAT; initially it was Ok, but then the flames went out and the horrid back puffing started. The night before I tried using less wood to start up the stove thinking there would be less outgassing from the lower heat once I added wood to the coals before engaging the CAT; same problem.[/quote]

Yeah. Does sound like a lazy draft. Weirdly enough, sometimes a short flu with a large diameter liner just won't pull hard enough to move air through a woodstove to make it go.

Old fart once said that the chimney is the engine that makes a woodstove or fireplace work. It's where it gets it's power. Not enough, or too much, and it won't work the way it should. The "mix" won't be right and you'll have trouble ranging from little to no fire, to too much fire, to backpuffing and smoke coming back into the house.

If the chimney is "just right" you can set a fire in a steel barrel and it will heat your house.

This will make your head spin and generate some conversation...

I'd have replaced the stove, as you did... or tried lining the chimney with the exact size of the minimum acceptable chimney flu size recommended in the VC manual that came with the stove. A smaller flu pipe will pull harder than a larger one on a short run or a long one, doesn't matter. I know, sounded stupid to me at first...

[quote author="grommal" date="1272550222"Well, in our case it was a short, exterior, uninsulated, masonry chimney. Exactly the recipe for NOT having overdrafting. Yet, we still had a completely unsolvable backpuffing issue with the old VC.[/quote]

LeonMSPT said:

Yeah. Does sound like a lazy draft. Weirdly enough, sometimes a short flu with a large diameter liner just won't pull hard enough to move air through a woodstove to make it go.

Old fart once said that the chimney is the engine that makes a woodstove or fireplace work. It's where it gets it's power. Not enough, or too much, and it won't work the way it should. The "mix" won't be right and you'll have trouble ranging from little to no fire, to too much fire, to backpuffing and smoke coming back into the house.

If the chimney is "just right" you can set a fire in a steel barrel and it will heat your house.

This will make your head spin and generate some conversation...

I'd have replaced the stove, as you did... or tried lining the chimney with the exact size of the minimum acceptable chimney flu size recommended in the VC manual that came with the stove. A smaller flu pipe will pull harder than a larger one on a short run or a long one, doesn't matter. I know, sounded stupid to me at first...

[quote author="grommal" date="1272550222"Well, in our case it was a short, exterior, uninsulated, masonry chimney. Exactly the recipe for NOT having overdrafting. Yet, we still had a completely unsolvable backpuffing issue with the old VC.

Click to expand...

[/quote]What's interesting is that the identical chimney pulls just wonderfully with the Oslo. I can easily do cold starts without even leaving any doors cracked open at all. Yet, it's completely controllable with just the single air lever on the stove. If it were a lazy chimney, I'd expect the Oslo to be pretty unhappy, since I'm dumping the 6" stove pipe into an 8" nominal flue. If it were a chimney that pulled excessively, I'd expect the Oslo to be difficult to control with a full load of super-dry wood on a cold and windy day. Neither of these is true.

The VC was supposed to have 8" flue, and we had the square-with-round-corners clay tile lining that's a little less than 8" across and has about the same area as the 8" round. The manual cautioned against using a smaller flue diameter, so we were already at the minimum.

Different stoves handle differently on the same chimney. I'm convinced that some stove designs simply are more finicky about the chimney/draft than others. I had a horrible experience with my VC Encore NC for the one season that I burned it. Same chimney worked great with my Fireview. Other folks are quite happy with their Encore NC stoves - same stove, different home and chimney. It seems that there are a lot of other stoves that, like the Fireview, can tolerate a wider range of chimney conditions and burn very well. Then there are "those other stoves" which simply must have exactly the right conditions to burn well.

I'm glad to have a more flexible stove now - weather and other things can affect the draft very easily and thus I'd rather not have a stove that is finicky. I would guess that the Oslo may well be in the same camp - able to handle a wider range of draft conditions well. The pattern of stoves that don't do well? Hmm.. seems to me to be the 'modern' (i.e recent) VC stoves (cat and non-cat) and any of the NC "Downdraft" style stoves. I'm sure there are others too - but I haven't done any real tallying of posts and/or reviews so my impressions may be way off base here.

Slow1 said:

Different stoves handle differently on the same chimney. I'm convinced that some stove designs simply are more finicky about the chimney/draft than others. I had a horrible experience with my VC Encore NC for the one season that I burned it. Same chimney worked great with my Fireview. Other folks are quite happy with their Encore NC stoves - same stove, different home and chimney. It seems that there are a lot of other stoves that, like the Fireview, can tolerate a wider range of chimney conditions and burn very well. Then there are "those other stoves" which simply must have exactly the right conditions to burn well.

I'm glad to have a more flexible stove now - weather and other things can affect the draft very easily and thus I'd rather not have a stove that is finicky. I would guess that the Oslo may well be in the same camp - able to handle a wider range of draft conditions well. The pattern of stoves that don't do well? Hmm.. seems to me to be the 'modern' (i.e recent) VC stoves (cat and non-cat) and any of the NC "Downdraft" style stoves. I'm sure there are others too - but I haven't done any real tallying of posts and/or reviews so my impressions may be way off base here.

Click to expand...

I agree. I firmly believe that we had an unworkable combo of stove and chimney (though we fought to make it work for 23 years!).

It's a shame there's no way to tell ahead of time exactly how a given stove will behave on a given chimney. Trial and error is a pain and could be quite expensive.

When we bought the Oslo, I almost decided to have the chimney lined with a 6" liner and/or possibly get some fancy chimney cap that creates more draft, because of the problems we had with the VC. I'm glad I decided to just give it a whirl without any chimney mods, as it turns out they were completely unnecessary.