Hot burn-out?

[spuldup]

First year wood-furnace owner here.
This time of year we'll have weeks off on where is could be high of 40F or 70F. On the 40F weeks I have been running our Brunco WC 190 (1984 model, UL listed), but once the cold front leaves, I let the fire burn out. Every time so far this has left a bunch of creosote in the firebox and even ran out of the ash door. Is there a way to burn this out hotter at the end of a fire? I figure cracking the ash door would do it, but the manual says never to do that. Unit is in the basement of a tall 2 story house and goes up about 32' to vent cap.

 

[moresnow]

Every time so far this has left a bunch of creosote in the firebox and even ran out of the ash door.

Are you speaking of liquid?

 

[begreen]

How well-seasoned is the firewood? Has it been tested for internal moisture content?

 

[Ashful]

Sure sounds like wet / green wood. I know it's common for boiler owners to think they can burn wet wood, in fact some of the marketing states as much, but this would be a normal result of following such advice.

 

[spuldup]

@moresnow Yes, thick black liquid drips out of the front of the ash door on the last burn.

I'm using a pinless moisture meter and only burning hardwood (that was standing dead on the property) under 20% moisture now (end grain checked) , but a few greener logs might have snuck in the first few burns. Still, only saw the creosote every time I let the fire go out. Next fire it all dries up and flakes down. The chimney looks clean, no layered buildup inside the stainless pipe.

Update: I just met with a chimney company (CMT Chimney in OH - very nice folks) and they pointed out that my vent is undersized. 8" from the furnace is reduced to 6" going up the all-fuel vent! That can't be helping. I am going to bite the bullet and have it all replaced with 8" insulated pipe.

I'll make sure to check every piece going in for moisture since I have such a hodgepodge of wood sources going on right now.

 

[moresnow]

@moresnow Yes, thick black liquid drips out of the front of the ash door on the last burn.

I'm using a pinless moisture meter and only burning hardwood (that was standing dead on the property) under 20% moisture now (end grain checked) , but a few greener logs might have snuck in the first few burns. Still, only saw the creosote every time I let the fire go out. Next fire it all dries up and flakes down. The chimney looks clean, no layered buildup inside the stainless pipe.

Update: I just met with a chimney company (CMT Chimney in OH - very nice folks) and they pointed out that my vent is undersized. 8" from the furnace is reduced to 6" going up the all-fuel vent! That can't be helping. I am going to bite the bullet and have it all replaced with 8" insulated pipe.

I'll make sure to check every piece going in for moisture since I have such a hodgepodge of wood sources going on right now.

Checking end grain means nada. Take a few room temp splits and re-split them. Check the newly exposed inner face immediately with pins inserted along the grain. Report what you find if you get a moment. Good luck.

 

[brenndatomu]

Update: I just met with a chimney company (CMT Chimney in OH - very nice folks) and they pointed out that my vent is undersized. 8" from the furnace is reduced to 6" going up the all-fuel vent! That can't be helping. I am going to bite the bullet and have it all replaced with 8" insulated pipe.

I doubt that is causing your creosote...especially if its been that way since 1984 and all of a sudden you are having an issue. I wouldn't spend my money on that unless you need a new flue for other reasons.
Sounds to me like its just wet wood...which if I were having this problem I'd make sure to set the thermostat to make the combustion blower run right to the end...don't let that fire smolder! You also may be loading too much fuel for the temps we are having right now...and "too good" of wood...don't use your oak right now, use the "junk" or shoulder season wood...pine, poplar/cottonwood, silver maple, box elder, etc etc...that stuff dries quickly and burns faster, so you wont over heat the house so quickly in warmer weather...and then you are saving the good wood for cold weather when its actually needed too...saves your "good stuff" stash!

 

[spuldup]

Thanks for the tips on checking fresh split.

And on the vent: the wood burner has only been in this house since 2004-2005 (when built), and the owners only used it once or twice, and once "smoking the house out". Granted, they were idiots based on this any several other little "finds" I've encountered in our 5 months there so far. Anyway, the unit was not ran much, and it was not run well. I came into possession of it with dead birds and nails in the firebox, ashtray 200% full, you get the picture.
Definitely if I knew it ran w/o issue for 30 years that would change my opinion of rerunning the vent, but I'm gonna do it. If anyone needs about 25' for 6"/8" Metalbestous-type.

 

[brenndatomu]

That unit should run fine on 25' of 6"...about the only thing it may affect would be possible smoke rollout if you open the door before the wood is burnt down well, or maybe if there is lots of hot coals and the wood starts to catch good before you are done loading.
It should draft just fine as far as how it operates though. Not the cause of your creosote...just so you understand that.
I assume this is stainless doublewall (insulated) chimney pipe? Not triple wall? (air cooled) Doublewall/insulated is much better for wood burners...

 

[Ashful]

The wrong vent size could have contributed to that "smoking the house out", but let's get a look at that wood moisture content. @moresnow gave the proper procedure. Splits don't need to be exactly room temp, but shouldn't be frozen either. Most important factor is checking on the freshly-split face, esp. with pinless meters.

 

[spuldup]

I assume this is stainless doublewall (insulated) chimney pipe? Not triple wall? (air cooled) Doublewall/insulated is much better for wood burners...

Yes is is doublewall insulated. The top 8' above the roofline blew off in a storm (because it did not have a roof anchor), and became damaged. And because of my inability to get on a roof 25+' above ground, I am using a company which must repair it to code. I seriously thought of putting a 8" to 6" stovepipe adapter at the roofline, and running 6' of 6" stove pipe to a vent cap, but if the house burns down and it's not to code, insurance does not pay for it. I have too many years of my life wrapped up in this property and I can't lose that. Even though I'm 99.999% sure it'd be fine for decades. My camp "cabin" up in the Allegheny National Forest has a single wall pipe off the wood burner, flashed with a street sign. Works just fine, I know!

 

[LogCabinFever]

Sounds like green wood may be the culprit to me too.

Another possibility is letting that furnace idle too low will yield excessive condensation from the cooling of the flue gasses. I have an old Jensen that will do a similar thing, although not liquid. The older furnaces were just not good at shoulder-season heating. They can’t idle really low and they function best to get it real hot. We normally use a freestanding cast Vermont castings stove this time of year and switch over to the furnace when night temps are steadily below freezing. It’s what I’ve found to work best.

But the liquid is different than what I’ve experienced

 

[spuldup]

Sounds like green wood may be the culprit to me too.

Another possibility is letting that furnace idle too low will yield excessive condensation from the cooling of the flue gasses. I have an old Jensen that will do a similar thing, although not liquid. The older furnaces were just not good at shoulder-season heating. They can’t idle really low and they function best to get it real hot. We normally use a freestanding cast Vermont castings stove this time of year and switch over to the furnace when night temps are steadily below freezing. It’s what I’ve found to work best.

But the liquid is different than what I’ve experienced

Very true! The pyrometer hovers between "creosote" and "burn range" while keeping the house 70F. We have the heat pump for shoulder months but it blows only warm (~90-120F) air and is loud. The wood furnace is almost silent and blows ~160F air. Floor is also warm, like radiant heat. Once the 8" vent is in and I've got some more burns with <20% fresh split wood, I'm hoping for some better performance.

 

[brenndatomu]

The older furnaces were just not good at shoulder-season heating. They can’t idle really low and they function best to get it real hot.

Totally agree...that's why I suggested loading lighter, using lower BTU wood, and then make sure the combustion blower runs right to the end of the fire...at least for say the second half of the burn...maybe even the whole time. This would only be for this time of the year...once "real winter" starts then SOP applies...

 

[Ashful]

Once the 8" vent is in and I've got some more burns with <20% fresh split wood, I'm hoping for some better performance.

You will definitely get more heat into your living space with dryer wood. Boiling water out of wood consumes a lot of the energy that would otherwise end up heating your house.

 

[spuldup]

Totally agree...that's why I suggested loading lighter, using lower BTU wood, and then make sure the combustion blower runs right to the end of the fire...at least for say the second half of the burn...maybe even the whole time. This would only be for this time of the year...once "real winter" starts then SOP applies...

Thanks for this advice, again! Can you tell me what SOP means?

 

[stoveliker]

standard operating practice
(i.e. see the manual, if you have it).

 

[LogCabinFever]

Totally agree...that's why I suggested loading lighter, using lower BTU wood, and then make sure the combustion blower runs right to the end of the fire...at least for say the second half of the burn...maybe even the whole time. This would only be for this time of the year...once "real winter" starts then SOP applies...

Exactly. I usually have a “chunks” pile that has stubs and gnarly pieces that I go through before heading to the good stuff in the shed. Lower BTU that won’t heat you out of the ho.

 

[brenndatomu]

standard operating practice
(i.e. see the manual, if you have it).

Yes...or Standard Operating Procedure.

 

[spuldup]

Yes...or Standard Operating Procedure.

Ah, I'm familiar with that. Thought it was some special wood burning acronym. Again, thanks for all the insight!

 

[JMihevic]

I have a Tarm MB 55 boiler I have used over forty years. I never start a fire until it is 30 Degrees outside. The house heat load is not enough and the Samson draft regulator controls the flapper nearly closed. I have the dial on the upper door open about one third of the way . With that small amount of secondary air, the primary air control is at the closed position. At this operating point, I can get creosote build up on the flapper door-- enough at times, to have the flapper get stuck in the closed position.

Above 30 degrees, I use my heat pump to heat my house.

John M.