Puffing cat Defiant Encore

Our Encore has started puffing smoke out from around the griddle occasionally, and nothing I can do seems to effect it. We got a terrific chimney, so I can't believe that draft can be the problem (about 25" from flue to top, rises well above nearby roof peak, 8" round ceramic flue tiles). I've also tried opening a door or window to see if that helps, and it doesn't. Puffing is very slight, just a quick wisp or two, so you have to be looking right at it to notice it and even then it can be almost subliminal.

Stove is 20+ years old and was rebuilt last winter with the full fireback/refractory kit, for the second time.

Outside conditions seem to have little effect - we have caught it puffing when it was warm outside and when it was cold, and when it is windy and when it is dead still, and at any thermostat setting from lowest to highest.

Generally happens with a well developed wire, that it is say, some hours into a burn and, of course, only when the stove is in downdraft. The wood we are using is not two-year bone dry, but pretty good dry cut early spring and stored inside.

The griddle seal was replaced a several years earlier, not as part of the rebuild last year, but passes the dollar test. I am tempted to replace it anyhow, but my feeling is that smoke can always find a way to get out if the pressure inside the stove gets higher than the pressure outside, and that it is the draft, not the airtightness of the stove that keeps the smoke where it belongs.

The first time it did this I cleaned the cat, which was fairly obstructed, and it seemed to cure the problem for a while, but it started puffing again a few weeks later (or we may have never stopped, but we just didn't notice, as it doesn't happen continuously). I cleaned the cat again, but it made no difference.

I thought the problem might be that the thermostat was starving the fire too much so it would have mini-explosion when it got a hit of air, like an old Shenandoah, but it happens even when the air door is open.

One possibility. We are currently using a stainless steel catalyst from Condar. The holes in it seem smaller than on the ceramic style, and may be just clogging easier. Still, you'd expect it would go more than a week without cleaning.

Just caught it in the act! Nothing subliminal about it this time . the stove would make a pop, and there would be a flash of flame in the firebox, and then a big puff of smoke would shoot out from all around the griddle/door. This is the worst I have even seen it, usually its just a wisp of smoke with no audible explosion.

It did this about ten times in a row, with about half a minute in between, very regular, would have probably kept on indefinately if we hadn't fiddled with it.

Stove was about half filled, and the wood well pyrolized - at the point where it is like charcoal and you can crush the logs apart with a shovel or poker.

This is pretty much the classic burn-off behavior typical of an air-starved fire in an tight stove. Odd thing is, the thermostat was open almost all the way, and the air door on the back that the thermostat controls open a good 1/4" at the bottom. So it seems clear that the firebox is being starved for air, but not as clear why it should be since the thermostat and primary air door were not shut down. . Oh, the ash tray was just emptied so that's not the problem.

If it had been a few years since the stove had any major servicing I would be tempted to pull it apart and clean all the air passages, but since it was rebuilt less than one burning season ago it seems unlikely that's the problem.

I pulled some of the doors and covers off the stove, and vacuumed out all the air passages I could reached, then removed the catalyst for the third time this year, and gave it the full Condar boiling-vinegar cleaning. Checked the operation of both thermostats and air feeds. Put the stove back together and it seemed to be running fine, only to wake up in the middle of the night to the smell of smoke, and find the stove was up to its old tricks puffing out rythmical blasts of smoke. Thermostat was half way open when this happened, and the air door it controls about 1/3rd open, so the fire was not being starved for air too badly. Did the same thing the next afternoon.

I really could use any suggestions about this - we don't dare burn the stove at less than wide open since it seems to puff smoke at any thermostat setting less than wide open, and quite regardless of wind or temperature.

The odd thing is, even with the cleaned, almost new, cat, the fire seems a bit subdued in downdraft - with the thermostat wide open, an established fire and good, dry, wood, it doesn't want to go above 500 (griddle). It seems to me something must be blocked either on the input (air) or output (smoke) side. Since I have checked both of them that would seem to leave the cat as the only possible culprit. Unless anyone has better idea, I can't think of anything left to do but replace the almost-new cat.

What's so odd about it, is that we got 20 years stellar performance from it in exactly the same spot where it is now. Some tendency to very slight puffing under certain atmospheric conditions as it got older, but that was easily corrected by just not closing the air down all the way. So I am at a loss to figure out what could have changed enough to so radically alter its personality.

grommal said:

Ours used to do the same thing. No setting of the air lever would solve it. Gangbusters draft the instant the damper was opened, so poor draft wasn't the problem. We struggled with the temperamental beast for many years, and finally gave up. Hope you have better luck.

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Condar has some really interesting stuff about cat life on their website at
http://www.woodstovecombustors.com/replacement.html
They say that after 12,000 hours of use a cat will have lost 25% of the catalyst on it, and should be replaced. There's a chart showing how many years that works out to in different parts of the country, depending on heating season. Where I am they show an expected life of about 2-1/2 years! This is far short of the guarantee period, so apparently Condar lnow the cat will not last out the warranty, for serious woodburners at least, and expects to routinely replace cats under the pro-rated warranty.

What's really interesting is that Condar does not claim or guarantee the steel cat to last any longer than their cheaper ceramic cat - same coating of catalyst on both, so life is expected to be the same - assuming both are equally well treated so they wear out before they self-destruct. This is the big if, since the ceramic cats often crack and fall apart before the catalyst wears out. But then the steel cats, while they don't crack, have their own ways of failing. And the steel cat does light off faster.

Mandoo said:

would like to say this stainless Cat is way better than the original but the stove runs about the same it does light off faster and I can only hope it lasts longer.

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