Cats clog before chimney?

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New Member
Jun 28, 2020
Hi all,

So as I get a little more comfortable with my new wood stove (Hearthstone Green Mountain 60) I am also starting to operate it more with the bypass and air control closed to extend burn times. It seems to stay in the "catalyst active" range fairly well, but I still worry about the slower burn causing more creosote and clogging up the chimney.

Would it be wrong to assume that if significant creosote was making its way up the chimney that the cats would clog first? I've cleaned out the cats once this season and they were fairly clean, which makes me think that the chimney wouldn't be building up too much creosote either. I'm sure the temperature of the cats is hotter than the stove pipe, so perhaps my assumption would be wrong based on that alone since the higher temperature of the cats might be hot enough to burn off creosote that wouldn't burn off in the chimney.


Minister of Fire
Feb 16, 2014
As long as your wood is at 20% or lower in moisture the cat will burn off the majority of violets reducing potential build up. And no, the chimney will clog before the cat unless you have very high draft (.15 or above) and fly ash gets sucked into those little squares on the combustor.
When operating a cat stove please remember only to engage the combustor when the cat probe is in the active range. Many new stoves that have cats, have the ability to run at lower temps, since many of the new stoves are also higher efficiency units, flue temps are lower then there older model counterparts, this is why many manufactures require an insulated liner when connecting the stove to any existing masonry chimney, or they require double wall black pipe vs single wall between the stove collar and main chimney, already lower flue temps have a greater potential to condense (<250deg f) and cause build up in the system, this is even at a greater chance if your burning sub par wood with higher moisture content.
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Feeling the Heat
Jan 8, 2017
Northeast Georgia
I have a Englander NC 30, no cat with 26 feet of insulated liner since 2016. I find myself turning it down here in NE Georgia because it just gets too hot inside the house. That is, I usually end up pushing the air control all the way in to cut down the air supply.
When I clean my chimney I usually get 1/2 to 3/4 of a small coffee can of ash and creosote.
If you are worried about the creosote, I suggest:
1) Cleaning the chimney at least once a year.
2) If you think you are getting the glossy variety of creosote, you might try one of the creosote "remover" products which actually just changes the creosote to a looser form which is easier to remove with a brush. Check with your manufacturer to see if this may affect the cat.
But if this your first year wait and see how the chimney looks this spring. You may be surprised at how little build-up will occur inside the top of the chimney.


Minister of Fire
Dec 28, 2006
Mt. Rainier Foothills, WA
Cat stoves burn cleaner at low output. The smoke has more time to react as it slowly passes through that blazing hot honeycomb.

Go outside, look at the chimney cap. No smoke? You’re good.

Oh and your cat may clog with ash from the firebox or creosote if you engage too early. Mine has never clogged after burning 32 or so cords. Your chimney should never clog unless you have a silly bird screen on it. Those screens can clog. If you’re burning even relatively well your chimney accumulation should be less than 1/4” thick per year.
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