Excessive creosote

[cbova]

Hello,

First time here, tons of good info.

I have a Vermont Castings Resolute (1985 vintage, 2 front doors) that was in our house when we bought it 3 years ago and have used it as the primary source of heat. I've had to clean the chimney at least twice a season because of crusty creosote blocking the flue. Here is a little background info; 7" square clay lined brick chimney, single story ranch house. 6" round stove pipe into flue, mix of hardwood split 1-2 years ago in covered 3 shed (open on one end). I have a thermometer on the stove pipe (so I can see it from the couch) maybe 12" up from the griddle and average 400°. I always run with damper open as it seems to run too cold with it closed. I put the thermometer on the griddle top last night and it was a good healthy temperature, slightly higher than the stove pipe.

A few nights ago I was running in fire place mode (doors open) and all of a sudden I started to get that smokey smell and you can feel the heat coming out of the doors rather than up the flue. I shut the door and let it burn down. The next night I went up on the roof and the flue was almost totally blocked with light crusty creosote about 2 feet up from the thimble. I just cleaned it in the beginning of this season and it has only had light use so far... what is going on? It seems to happen all of a sudden, has done it once before but it was later in the season so I just figured it was 'time'. I had been running in fireplace mode for the past few weeks but the flue temp was good (wasn't too cold) so I figured it was fine.

My wood is well seasoned, proper flue and stove pipe size, what else could cause this? I'm wondering if the thermometer is out of whack and showing higher than it is, it looks as old as the stove. My wood consumption is good, heat output is more than enough for the 1200 square for ranch. No problems with draft when the chimney is clear.

Should I run it hotter? Is my wood not seasoned as well as I thought? I recently replaced windows but draft is good when lighting so I doubt that has anything to do with it. I also have a big cast iron crock with water on the griddle all of the time, is that sucking the heat of the exhaust gasses?

Next question: I noticed while I had the stove pipe off that the fireback (behind the damper right below the outlet) is filling with ash... do I need to clean that out? I didn't see anything in the manual under service and maintenance about that.

Thanks,
Chris

 

[oldspark]

Are you running it at a lower temp overnight?

 

[Redbear86]

A moisture meter might be the easiest thing to start with

 

[coaly]

Clean-out door or opening into chimney allowing cool air to be pulled up the flue, cooling the inner flue temp? The target temp to stay above is 250 all the way up to prevent condensing. You will need to let more heat than necessary up your chimney since it is quite a bit larger than the stove outlet. 1 inch doesn't seem like much, but..... 6 inch round is 28.26 square inches. (pi X R2 or 3.14 X 9) The 7 inch square is 49 square inches. So you're trying to heat almost twice the area of your pipe.

 

[Agent]

If you've been burning intermittently, I'd imagine the cold clay tile transition to be a creosote magnet every startup.

 

[Battenkiller]

Clean-out door or opening into chimney allowing cool air to be pulled up the flue, cooling the inner flue temp? The target temp to stay above is 250 all the way up to prevent condensing. You will need to let more heat than necessary up your chimney since it is quite a bit larger than the stove outlet. 1 inch doesn't seem like much, but..... 6 inch round is 28.26 square inches. (pi X R2 or 3.14 X 9) The 7 inch square is 49 square inches. So you're trying to heat almost twice the area of your pipe.

+1

Personally, I'd install an insulated liner in that flue. I think that will solve all your problems and allow you to keep the heat in the room where it belongs.

 

[Battenkiller]

Should I run it hotter? Is my wood not seasoned as well as I thought? I recently replaced windows but draft is good when lighting so I doubt that has anything to do with it. I also have a big cast iron crock with water on the griddle all of the time, is that sucking the heat of the exhaust gasses?

Next question: I noticed while I had the stove pipe off that the fireback (behind the damper right below the outlet) is filling with ash... do I need to clean that out? I didn't see anything in the manual under service and maintenance about that.

Just noticed these comments. Yes, that big pot of water can have an effect on flue gas temps in the vertical burn mode. The ash should be clean out of the stove as well. Last year I wasn't getting the heat I wanted out of the stove when in the horizontal burn mode. On advice here on Hearth I let the stove cool off, emptied all the ashes and vacuumed and blew out all the passages in the intake air and behind the fireback. The stove jumped up another 50-100º or so in stove top temps under the same burn conditions. Just routine maintenance, I learned.

 

[remkel]

Yup, the ash buildup will restrict air flow to the fire. Clean that out and you should see the increased performance Bk mentioned above.

 

[cbova]

Thanks for all of the responses. I will definately consider all of them. In the mean time I will monitor the griddle top temps (with and without the crock) and see how they compare to stove pipe temps. Next time I have the stove pipe off I will clean the ash out of the fireback too.

I did check my clean-out in the basement, it is closed, not air tight but closed.

 

[Jack33]

If you have never done it, you need to clean out the area under the damper. Remove the flu collar and close the damper to access underneath. If really bad, you may need to clean out the side area also. When I ran a single door Resolute I would clean it out at least once during the burning season, sometimes twice. Also try to keep ash away from the right side covering up the exhaust exit so it doesn't get sucked into the side. Also, the "hollow" fireback is cemented together. When the cement crumbles away, it allows cool intake air into the exhaust passage and vice versa.

I ran mine on a 7x11 chimney. It was a creosote machine that I shoveled out by buckets once a year. I would also double check the accuracy of your old thermometer.