New to the forum - Just how bad is 35-40% moist wood?

[Woody06]

Hi All,

I'm new to posting on the forum but not necessarily to wood. I studied biomass gasification for fuel production in grad school. I've recently moved from the city (Boston) to 20 acres in Western Massachusetts and have caught the wood bug. I can't see a downed tree without experiencing the overwhelming urge to cut it up and split it.

So on to my question. The house we bought has a Harman SF-250. As many of you probably know these are monstrous pre-EPA stoves designed to be dual-fuel wood/coal. Eventually I'd like to get a catalytic stove (probably Blaze King) but for now this is what I have to burn with.

We moved in in January and I had some time to cut about a cord of downed wood before it snowed. It was felled about a year or two ago, but still has 30-40% moisture content.

If I can keep my stack temps in the 400-800 F range (internal probe) am I ok to burn this stuff? It seems like if the stack is hot creosote won't be too much of a problem.

We have oil central heat so the wood is not critical and is only burned some evenings and weekends. Do the experts out there think this is a bad idea? Any other thoughts?

Excited to be a part of such a knowledgeable community!

 

[begreen]

Sounds like some of that wood is almost half water. That is going to be hard to burn. Bring a bunch of totes full into the dry living space and give them a couple weeks. That should bring it down to maybe 25-30% which will burn. Be sure to keep a close eye on the chimney. Instrumentation is great, but I would also do a visual check frequently to watch for buildup. How quickly it will build up depends on the flue configuration. If you can mix in some dry cut up palette wood that will help.

 

[Woody Stover]

When I first started reading at hearth.com and got "dry-wood religion," I cut up a fallen White Ash, split a half-cord fairly small fairly small, stacked it in the house with a fan blowing on it and got it to 20% in a couple weeks....but it started at about 25%.
With 20 acres, a better plan would be to look for small, dead trees (<8",) standing or down. Much of that stuff will be in the low-20s range.
That said, start working on next season's wood now, but put any Oak or other dense wood into a separate stack for a couple or three years down the road. You need fast-drying species like soft Maple or Black Cherry for next winter.

 

[Woody06]

Thanks for the thoughts! Yeah the stuff I cut back in November was ~30% moisture and actually burned pretty easily. The weather turned wetter and I've had a hard time scrounging for anything under 35% and it is proving more difficult to keep stack temps above 400 F.

I did walk around the woods with a hatchet and meter and found a couple standing dead pines at about 25%. I will plan to go for those next. I think my problem was that I found some beautiful downed oak and couldn't resist the urge to harvest it.

I have experimented a bit with drying indoors. Stacking next to the stove with a fan blowing through it seems to help. Being an engineer I even went to the length of building a system that pulls heated air from the stove through a chamber filled with wood, but the smell and dust generation was a bit much, especially because my wife has allergies.

In general I'm a little concerned with having too much wood in the house at a time, given that it is a post and beam house and I would hate to get some sort of an infestation. I'm also a little worried about stuff that's been lying on the ground for a year releasing mold spores.

I'll plan to go for the standing dead pine right after we dig out of the 18" of snow we just got.

 

[bholler]

I would burn coal til you can get a good supply of useable wood. 30 to 40% to me is not usable at all in your stove even upper 20s will work ok because of how the stove works but over 30 is going to be a real fight. But you will be much happier if you get stuff that is below 20% you will get more heat out of the wood and less creosote.

 

[Woody Stover]

I did walk around the woods with a hatchet and meter and found a couple standing dead pines at about 25%. I will plan to go for those next. I think my problem was that I found some beautiful downed oak and couldn't resist the urge to harvest it.

Hatchet and a meter...you're well on your way. The wood needs to be at 50* before you split and test it. Colder wood will read false low. You may get away with marginal wood in the old stove but once you get a newer EPA-certified model, that wood won't cut it. I get decent burns starting at 20%...18 is when it really gets good. Resist the urge to burn your wood before it gets to that point; You've put in all that work, but you'll reap mostly frustration...having to tend the fire more, and getting less heat than you should be.
Keep a close eye on your flue for any buildup; If you throw some of that drier Pine in there and start tossing heat up the flue, that's when you can ignite the creo buildup if it's present.

 

[Woody06]

Yeah, I've found empirically that frozen woodpile wood that reads 20% can read 40% indoors. I've started to get calibrated on how wood feels/sounds at the varying levels and then test once it has thawed.

Out of curiosity, why are the newer EPA stoves harder to run with wet wood? From an intuitive standpoint I would expect it to be easier. I have to work pretty hard to keep live flames and avoid smoldering, but can't a cat stove burn the smoke from a smoldering fire? I'm sure I'm missing something here. Maybe the presence of steam makes it harder for the oxidation reaction on the catalyst?

It's funny because my graduate research was on heating up wood and reacting it with steam to make hydrogen and carbon monoxide. Steam was good in that case.

 

[Woody Stover]

Yeah, I've found empirically that frozen woodpile wood that reads 20% can read 40% indoors. I've started to get calibrated on how wood feels/sounds at the varying levels and then test once it has thawed.

Sound can be deceptive at times. Some splits will 'ring like a bell,' yet still be pretty wet. Once you get a feel for the heft of different species when they are wet vs. dry, you can make a pretty good 'guess-timate' as to what you're dealing with. Also, you can press a fresh split against your cheek or lips...wet wood will feel cooler due to evaporation. I have to warn you, your wife may feel offended if she sees you starting to kiss wood.

Out of curiosity, why are the newer EPA stoves harder to run with wet wood? From an intuitive standpoint I would expect it to be easier. I have to work pretty hard to keep live flames and avoid smoldering, but can't a cat stove burn the smoke from a smoldering fire?...It's funny because my graduate research was on heating up wood and reacting it with steam to make hydrogen and carbon monoxide. Steam was good in that case.

I don't know much at all about gasification but I think the problem in EPA stoves (cat or non-cat) is that they have to be at a certain temperature for the re-burning of smoke to take place, and with wet wood, heat is lost evaporating the moisture. You have to compensate by opening the air more to get the wood burning, and then more heat is wasted up the flue. Seems counter-intuitive that a cat wouldn't handle it better since they burn smoke at 500* vs. 1000 or so for a non cat, but I think the consensus here is that non-cats are a little more tolerant of wet wood. I've never run an EPA non-cat. OTOH, I have seen posts by @webby3650, and on the Woodstock site, saying that cats can handle wet wood OK.

 

[bholler]

I have to work pretty hard to keep live flames and avoid smoldering, but can't a cat stove burn the smoke from a smoldering fire?

the smoke can only be burnt if the temperatures in the box or on the cat are high enough to maintain secondary combustion. And with wet wood you wont get that till you drive that moisture off. And the massive amount of steam released can destroy cats to btw. And most older stoves dont deal with wet wood all that well either but yours being a coal stove where the air is introduced from under the fire it will work better. But I would still use coal till you get your wood dry.

 

[PA. Woodsman]

This might get more attention if it was in "the wood shed" thread, no?

 

[BKVP]

It's very clear (no pun) that when the water in the wood is burned off, it reduces firebox temps which has four consequences.

1) Dirtier Burn (more emissions)
2) Lower Cat Temps
3) Lower Secondary Combustion Temps
4) Lower Efficiency

We have thoroughly experimented with the issue of moisture in fuel and would suggest that all wood stoves, regardless of clean burning technology, be operated at higher burn rates for a period of time prior to lowering the burn rate. This is help deal with the first stage of combustion, dealing with the moisture in the load.

 

[tpenny67]

Thanks for the thoughts! Yeah the stuff I cut back in November was ~30% moisture and actually burned pretty easily. The weather turned wetter and I've had a hard time scrounging for anything under 35% and it is proving more difficult to keep stack temps above 400 F.

The weather in MA has been awful for firewood this year. I finally had gotten around to cutting up some small trees that were felled a number of years ago, and though they are partially rotten on the outside they should still burn if they get dry enough. Bitterly cold dry air seems to work well, until that warm and humid front comes in and hits the cold wood and the moisture literally condenses onto the wood. Follow that up with a heavy wet snow to rain event and you might as well have stored the wood in a pool.

 

[gzecc]

Starting from 0 with an old wood stove is a challenge. You'll need at least a couple of cords stacked and drying for at least 2 yrs. I suggest you get a couple of cords of ash, you can stack (split small) and hopefully use next year. You still need to process a couple of cords per year, to stay ahead. You need 4 cords stacked now, to start seasoning.

 

[Woody06]

Thanks everyone for the advice on selecting based on wood variety. I went back through the wood I have cut and found some more of the small cherry and maple that seemed to do well. It measures out at ~30-35% but I can easily keep stack temps at 600-800 F and actually have to watch out for overfiring. I don't run the stove continuously and when I do burn I usually try to keep it roaring just below overfire. I didn't realize that oak takes so much longer to dry. I'm working a site that was logged a year or two ago with a lot of small stuff left behind so I have my choice of wood type.

With these conditions it seems like I'm probably not going to get a whole lot of creosote deposition right? My stack is ~25 feet of ss lined concrete block with all but the last 4 feet in the house. I cleaned the chimney back in December and would get back up there to check other than the foot of snow and the 20 foot drop if you fall off. I guess the fall would be a little better with the snow on the ground.