Creosote in fire box

  • Active since 1995, Hearth.com is THE place on the internet for free information and advice about wood stoves, pellet stoves and other energy saving equipment.

    We strive to provide opinions, articles, discussions and history related to Hearth Products and in a more general sense, energy issues.

    We promote the EFFICIENT, RESPONSIBLE, CLEAN and SAFE use of all fuels, whether renewable or fossil.

vallieweck

New Member
Dec 15, 2025
10
Sw Washington state
Hello all. I run my BK hot for about 45 min on cold start or after reloading, STT at around 600-650 and then I start turning down the thermostat for temps to run around 400. Is it normal to still have creosote like this in the fire box and on the glass? Burning fir at 18%, I would like that to be drier but it’s what we have, still in acceptable range.

Thinking about using rutland’s creosote spray during a cold start for when catalyst in bypassed. Thoughts?

Thank you in advance!
 

Attachments

  • [Hearth.com] Creosote in fire box
    IMG_7876.webp
    262.8 KB · Views: 12
  • [Hearth.com] Creosote in fire box
    IMG_7875.webp
    225.6 KB · Views: 12
  • [Hearth.com] Creosote in fire box
    IMG_7791.webp
    125 KB · Views: 12
That’s perfectly normal, it’s part of the “low and slow” lifestyle. On that note how do you measure the MC of your firewood?
 
Took a split of wood that had been inside the house over night. Chopped her in half and took a reading with a probe on the ends and in the middle.
Perfect method, 18 is acceptable. Even with drier wood you still get sheets of creo peeling off the inside of the firebox. A nice hot fire like your doing helps keep it in check.
 
Don't use Rutland creo spray - it's bad for the cat.
Even in bypass mode, how are you sure all bypasses the cat, and all is gone before you close the bypass?

BK says not to use it.

Creo in the box is fine. Your flue should remain clean if you use the stove/cat properly.
At the end of a season I run one load full throttle and then (steel) brush the crisped up creo out of there and vac it up to not have that oxidizing creo sit there all (humid) summer.
 
  • Like
Reactions: vallieweck
Don't use Rutland creo spray - it's bad for the cat.
Even in bypass mode, how are you sure all bypasses the cat, and all is gone before you close the bypass?

BK says not to use it.

Creo in the box is fine. Your flue should remain clean if you use the stove/cat properly.
At the end of a season I run one load full throttle and then (steel) brush the crisped up creo out of there and vac it up to not have that oxidizing creo sit there all (humid) summer.
Thanks for the reply. Even burning hot..this creosote doesn’t “crisp” so that I can brush it off, seems like a lacquer!
 
A full load white open throttle?
I've had sticky goo but after loading the firebox full and burning it down in a hurry, it's all coming off
 
No dialing down. Cold start, full load, close bypass when the cat is active, keep the thermostat fully open, let it do its thing.

Literally a full load wide open thermostat. Not 45-60 minutes. Just the full load. I.e. 8 hrs or so for me (depending on wood species).
 
No dialing down. Cold start, full load, close bypass when the cat is active, keep the thermostat fully open, let it do its thing.

Literally a full load wide open thermostat. Not 45-60 minutes. Just the full load. I.e. 8 hrs or so for me (depending on wood species)

No dialing down. Cold start, full load, close bypass when the cat is active, keep the thermostat fully open, let it do its thing.

Literally a full load wide open thermostat. Not 45-60 minutes. Just the full load. I.e. 8 hrs or so for me (depending on wood species
Thanks again but I am confused I think. Wouldn’t I risk burning way too hot for way too long? I imagine it would get over 1,000 degrees on the STT easy. Unless we are talking about just a couple smaller logs? I burn fir btw.
 
No. A full box. I've done pitch pine and oak (just what I had).

This is how the thermostat works: it'll close the air when things get too hot. Setting it at "fully open" means "the highest temperature where the flapper will close up", it does NOT mean "the air is and remains fully open".

Basically the thermostat of the BKs protects a stove against overfiring (as long as the stove is properly sealed (gaskets etc), proper fuel is used (dry pure wood), and the flue does not draft beyond specs (hence the flue recommendations - which are a proxy for the actual measured draft range in which the stove works well).
Of course doing any of this wrong (leaky stove and a 50 ft flue) will result in the system not being able to do what it was designed to do.

But doing things right you can burn a full load down wide open throttle without issue.
There was a guy here from Alaska who said that he burned like that months at a time.
 
  • Like
Reactions: vallieweck
No. A full box. I've done pitch pine and oak (just what I had). This is how the thermostat works: it'll close the air when things get too hot. Setting it at "fully open" means "the highest temperature where the flapper will close up", it does NOT mean "the air is and remains fully open". Basically the thermostat of the BKs protects a stove against overfiring (as long as the stove is properly sealed (gaskets etc), proper fuel is used (dry pure wood), and the flue does not draft beyond specs (hence the flue recommendations - which are a proxy for the actual measured draft range in which the stove works well). Of course doing any of this wrong (leaky stove and a 50 ft flue) will result in the system not being able to do what it was designed to do. But doing things right you can burn a full load down wide open throttle without issue. There was a guy here from Alaska who said that he burned like that months at a time.
Huh, interesting, logic makes sense. I get nervous when I see temps nearing 700* and always choose to turn the thermostat down. Guess I would really have to trust the process. At what temperature should I be concerned?

Our stove was installed by a qualified installer to spec so I feel good about that. Just swept it a couple weeks ago.
 
No. A full box. I've done pitch pine and oak (just what I had).

This is how the thermostat works: it'll close the air when things get too hot. Setting it at "fully open" means "the highest temperature where the flapper will close up", it does NOT mean "the air is and remains fully open".

Basically the thermostat of the BKs protects a stove against overfiring (as long as the stove is properly sealed (gaskets etc), proper fuel is used (dry pure wood), and the flue does not draft beyond specs (hence the flue recommendations - which are a proxy for the actual measured draft range in which the stove works well).
Of course doing any of this wrong (leaky stove and a 50 ft flue) will result in the system not being able to do what it was designed to do.

But doing things right you can burn a full load down wide open throttle without issue.
There was a guy here from Alaska who said that he burned like that months at a time.
I did not know this about the thermostat by the way, thank you! I thought you must turn it down some so it wouldn’t get too hot. Owners manual I don’t think went over this so now I need to read again!
 
  • Like
Reactions: stoveliker
Huh, interesting, logic makes sense. I get nervous when I see temps nearing 700* and always choose to turn the thermostat down. Guess I would really have to trust the process. At what temperature should I be concerned?

Our stove was installed by a qualified installer to spec so I feel good about that. Just swept it a couple weeks ago.
That's fine. We all learn things here.

How tall is your chimney from stove top to chimney cap?
 
Is this a new stove?

I had creosote as you described then after 30 or so fires it started to peel off. Big “peels” 2”-3” by 5”-6”. Can’t explain why it happened, maybe the creosote has to be a certain thickness before it starts to peel off?
 
Okay. No worries about overfiring due to a flue with too much draft