Chimney fire

[Ghost]

I had a chimney fire yesterday, turned my 6" single-wall into a torch for about 10 minutes. The temperature about 2' from the evaporator exit went from 130F to 700F. It occurred after about 40 hours of boiling total. It was probably because early on I burned a lot of pine and as a back-yarder on an uninsulated chimney it never got hot and likely creosote formed either in the chimney, in the evaporator after the baffle, or both.

Kinda wild.

[ecolbeck]

Was 130F the chimney temp? That's pretty cold and likely the cause of the creosote formation rather than the use of pine firewood

[Ghost]

Yes, about 2’ from the evaporator exit. Not sure how to avoid it or if it’s a problem. Insulated pipe was inconveniently heavy for this seasonal setup.

[ecolbeck]

Insulated pipe is not a necessity. All you need is wrist sized dry wood for a hot fire. You should be getting 10ish gallons per hour evaporation rate. Are you close to that?

[Ghost]

Yes, usually 11-12. The wood was dry, stored under cover for 18 months, mostly from summer 2019.

[ecolbeck]

Having a chimney fire just seems really unlikely if you consistently have hot fires. Can you tell us more about your setup?

[BCPP]

Are you saying the creosote build up has just been in past month or so? Seems unlikely that it could have built significant amount that fast if you're getting an evaporation rate like that. Also does not seem right that chimney temp could only be 130F, that's not even enough to boil water.Are you sure thermometer is working?

[maple flats]

I believe that's the first chimney fire I ever heard about on an evaporator. Creosote is generally built up when a fire is choked down and run too cool, not when it's fired hard. In 19 seasons I never cleaned my stack and it's single wall for 12 out of 17' total length. The 5' not counted is insulated from 1' below the bottom cord of the trusses up to the roof steel. My stack runs at 650F up to about 950F once it gets going.
In the off season did that pipe get used for another use? Maybe a smoker?

[Pdiamond]

You mentioned you had a baffle are you talking in the chimney pipe like for a wood stove to control heat loss? If you are using one lose it on the new chimney pipe. you want a straight shot out the evaporator and up the chimney.

[Ghost]

I was overloading the arch. Use of a timer to load more regularly, use of smaller wood, and less resulted in a happy stack temp of 350F

[Zucker Lager]

The temperature about 2' from the evaporator exit went from 130F to 700F.

Kinda wild.
I shoot for a stack temp around 700 through a 6" single wall at that same height above the arch. That seems to be the best boil for the buck for my little 2 by 3. There is never a build up in the pipe. Jay

[maple flats]

I agree 650-900 is far better stack temperature. Split the wood wrist size, criss cross it in the arch for more air flow and only fill about 2/3-3/4 full. Get a timer, start refueling every 7 minutes, if coals don't start to build up, go to 6 minutes. If coals build up significantly at either temp, try 8 minute intervals. One of those will prove right for your rig. Whichever it is, use that timing all of the time you are boiling. This will apply to all dry wood, hard or soft, either will work, but if a pine, remove as much bark as you can, pine bark actually protects the tree in a fire.
Years ago, I had 1 piece of pine that was so crooked it didn't lend itself to splitting, it was between 6-8" in diameter. I figured I'd just throw it in the fire and get rid of it. At the end of the night, I shut down, covered my pans (it had been in a true inferno for at least 4 hrs) and I left. The next morning I went to empty the ashes, that piece of ugly pine was only blackened and still whole. That was a Scotch Pine piece. I have a sawmill and have burned lots of hemlock and pine slabs, but I removed the bark before it went into the fire.

[ir3333]

i can't imagine firing every 7 or 8 minutes.I use larger wood and like to fire at a more relaxed 20- 25 minutes.
I like a good boil, a stack temperature as you say between 650 - 800 and no chimney smoke means you are burning clean.
Maximizing GPH is less efficient and wastes wood in my arch.
..'kinda like my car goes a hundred plus but it's most comfortable at 60 and gets excellent mileage!

[wmick]

Hard to understand a creosote problem with an evaporator... I'm typically thinking there's too much heat going up the chimney, rather than not enough...

Brings back a memory for me, though.
We heated the house with wood when I was a kid.... My dad worked away during the week, and Mom was always afraid of the stove, so she idled it too much..
Every weekend, my Dad would open the drafts wide and create a chimney fire intentionally, to clean the chimney. (bit of a controlled burn, I guess)
I remember seeing the reflection of the chimney flames on the cedar hedge behind the house when he did this process.
Good lesson for me, that I wont ever forget... Need to burn the chimney good and hot on a regular basis, to prevent an unwanted fire.

[ir3333]

i agree.. a hot fire and dry wood.( i still heat with wood...by choice)

[Woodsrover]

Sounds like you need more air, more draft or both. When I'm running happy my stack is 750-850 degrees 3 feet off the evaporator. Don't think woodstove in your basement, this is a different animal.

[maple flats]

i can't imagine firing every 7 or 8 minutes.I use larger wood and like to fire at a more relaxed 20- 25 minutes.
I like a good boil, a stack temperature as you say between 650 - 800 and no chimney smoke means you are burning clean.
Maximizing GPH is less efficient and wastes wood in my arch.
..'kinda like my car goes a hundred plus but it's most comfortable at 60 and gets excellent mileage!
That's your choice, but you will be boiling about 3x as long to get the same total evaporation. If that's what you are looking for that's fine, it's just not very productive. You can't think of a car in relation to an evaporator. Split your wood wrist size, fuel every 7 minutes and see how much better it does.

[ir3333]

Firing fast with small wood will increase my evaporation rate by about 15- 20 % with increased stack temperature
and loss of efficiency... I'm trying to increase my gph and efficiency by making changes to my equipment
each year until i hit the Sweet Spot.

[tapdrinker]

yes smaller wood-non green - dead for more than 1 yr and mix soft and hard woods.
I find this is my best boiling fuel at least wood wise. And cross the wood best you can.