Wood furnace creosote buildup

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BONKER 8130

New Member
Dec 3, 2021
6
Ohio
Hello there, newbie to the forum and wood furnaces. I'll jump right to it. I have a recently installed crown royall 8130 wood burning furnace, with a new single wall ss chimney liner. I am also new to wood burning in general. This is my 3rd winter burning wood. I have been using a brunco fireplace insert for the past 2 years and I'm getting a handle on what it likes and keeping creosote to a minimum. But with my new furnace it seems a bit more difficult to keep temps up to where they should be. I've been using magnet thermometers on the sp and on the front of the furnace. And it generally stays around 2-300 degrees f. But I recently used something like a stick thermometer and got over 400 on the inside of the sp. So just a little confused on that, owners manual say to be between 350 and 450 on stove pipe. And then on the same issue which has alot to do with things is the barometric damper ....full of creosote on the flap and no matter where I run it can't get below .08" water column. Thank you to anyone reading this and that can help!
 

maple1

Minister of Fire
Sep 15, 2011
10,964
Nova Scotia
Yes there is a wide variation between surface mount magnets and internal stems. It can be twice as hot in the middle of the pipe as on the surface. I would not shoot for 450 on the surface, that is way hot.

Are you actually measuring draft with a manometer?
 

BONKER 8130

New Member
Dec 3, 2021
6
Ohio
Yes there is a wide variation between surface mount magnets and internal stems. It can be twice as hot in the middle of the pipe as on the surface. I would not shoot for 450 on the surface, that is way hot.

Are you actually measuring draft with a manometer?
Well that's good to know on the temps. Yes I have a Dwyer manometer. Some more info on the chimney its about 25ft long inside of a masonry liner and brick. Its not insulated the installer couldn't get any at the time and said I might not need it anyway since it runs up the middle of the house.
 

brenndatomu

Minister of Fire
Aug 21, 2013
7,519
NE Ohio
Honestly it really sounds like most of the issue is wood that is not really dry.
If you grab a room temp split, resplit it, then test the center of the newly exposed faces with a moisture tester, whatya get?
 
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peakbagger

Minister of Fire
Jul 11, 2008
7,695
Northern NH
I am not familiar with the furnace, does this one control air flow as means of controlling heat output? (I.E. when there is no heating demand an air flap closes smothering the fire? ) If so that is going to crank out a lot of creosote whenever the flap closes unless you in the coaling stage. Add in marginaly dry wood and it can be difficult to get good temps in shoulder season when the furnace only needs to put out a low amount of heat.

A rough car analogy on the air flap is imagine instead of controlling the gas sent to the engine of a car that you tried to control engine speed by controlling the air flow into the engine. It might work but will involve a very dirty exhaust and backfires.
 
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BONKER 8130

New Member
Dec 3, 2021
6
Ohio
Honestly it really sounds like most of the issue is wood that is not really dry.
If you grab a room temp split, resplit it, then test the center of the newly exposed faces with a moisture tester, whatya get?
Well I have a variety, some ash that is 18-20 and some red oak that is 20-22. The manual calls for 20-25. The wetter stuff I have I only throw on top of the dryer stuff and on a hot fire.
 

BONKER 8130

New Member
Dec 3, 2021
6
Ohio
I am not familiar with the furnace, does this one control air flow as means of controlling heat output? (I.E. when there is no heating demand an air flap closes smothering the fire? ) If so that is going to crank out a lot of creosote whenever the flap closes unless you in the coaling stage. Add in marginaly dry wood and it can be difficult to get good temps in shoulder season when the furnace only needs to put out a low amount of heat.

A rough car analogy on the air flap is imagine instead of controlling the gas sent to the engine of a car that you tried to control engine speed by controlling the air flow into the engine. It might work but will involve a very dirty exhaust and backfires.
It has a 50 cfm draft inducer with a flap that is manually adjusted.
 

salecker

Minister of Fire
Aug 22, 2010
1,876
Northern Canada
Don't use any wet wood no matter the fire you have.
Wet wood causes creosote to form.
 
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brenndatomu

Minister of Fire
Aug 21, 2013
7,519
NE Ohio
20-25% is gonna make creosote, period. Sub 20% will do much better though...it eliminates A LOT of problems!
 
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laynes69

Minister of Fire
Oct 2, 2006
2,672
Ashland OH
In terms of modern burners, 25% is high. It takes alot of BTU's to boil out the water. Wood at 15% is ideal.
 
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brenndatomu

Minister of Fire
Aug 21, 2013
7,519
NE Ohio
Idk much about how much it takes to boil out but it's rated for 130,000 btu.
He's talking about the lost BTU's in drying the wood enough to burn properly
 

JRHAWK9

Minister of Fire
Jan 8, 2014
1,913
Wisconsin Dells, WI
In terms of modern burners, 25% is high. It takes alot of BTU's to boil out the water. Wood at 15% is ideal.
I completely agree. I know I've been loving my old firewood.

The other nice thing about burning dry wood is that one should be able to slow down the furnace's "engine" (draft) some. This helps keep more of the BTU's in the house vs sending them up the chimney. I'm burning 6.5 year old stuff now (anywhere from 12-18% when I have measured it) and I have dropped my draft down to -0.04" by way of my BD. I have then used my key damper (which is installed right after the collar between the furnace and BD) to drop it down even further to around -0.02" once the furnace goes to pilot. Doing this has been working really well for me if the temps outside are above 15° or so. I get even longer burn times. The bad part about using a key damper to even partially control the draft is that once the fire starts to die down, the draft will fall with it....and falling from -0.02" means hardly any draft and less heat output per hour. So when it's colder out I need to keep my key damper open in order to keep my draft at -0.04" throughout the whole burn in order to keep my heat output per hour up towards the end of the burn.

Here's my draft right now while it's been cruising on pilot now for 2 hours and firebox temps are such that it will be staying on pilot for awhile longer. Although this load was a handful of smaller pieces and was probably pretty darn dry. Was 11° outside when I left for work, but supposed to get up to 26°....so hence why I used the key damper to lower the draft on this load. Sorry for the bad photo, it's a screen capture from zooming in on my IP camera in the dark. It's at about -0.02", as the camera angle makes it look like it's a little over -0.01".

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