Cold Wood = Slow Start

[Backwoods Savage]

I do not like to have wood in the house unless it is in the stove. We have burned wood over 50 years and have never noticed a problem burning cold wood. It lights really fast so long as the wood is dry. But if you burn poor fuel, you will get poor results.

 

[f3cbboy]

this would be great if we get in to a talk about latent heat...

 

[Dune]

You have to calculate from absolute zero if calculating a % increase/decrease in temperature.

Wouldn't it be easier to calculate the calories (btus whatever) needed to raise x pounds of wood x degrees then subtract the 50 or so degree difference?

 

[firecracker_77]

I keep about 25 splits stacked up right next to the stove. I think that helps dry it a little bit at the end if it does have any surface moisture on it.

 

[Dakotas Dad]

We let our wood sit in the sun on the front porch for a week or so before it gets brought in and placed in a rack that holds *about* two days worth. I hate to have to go out on the porch at o-dark thirty to fetch three splits..

 

[ohlongarm]

I'm gonna settle this I'm putting 2 splits of 15% moisture content in my freezer,one cherry one beech. And 2 of the same in moisture content and size in my living room ,when I start my next fire ,I will throw 2 of each individually on a coal bed and time the ignition of both from when I lay em down to when they're fully engulfed will report back with the results. With pics if I can remember how to post it's been awhile.

 

[woodmiser]

It might be more than just temp differential. Throwing a cold load of wood into the stove on a kindling fire also changes the whole environment of the inside of the stove. All I'm saying is when i threw the cold splits in there the kindling practically went out. Maybe I just snuffed it down with the wood... who knows.

 

[HotCoals]

I'm gonna settle this I'm putting 2 splits of 15% moisture content in my freezer,one cherry one beech. And 2 of the same in moisture content and size in my living room ,when I start my next fire ,I will throw 2 of each individually on a coal bed and time the ignition of both from when I lay em down to when they're fully engulfed will report back with the results. With pics if I can remember how to post it's been awhile.

Maybe run some water over one of the ones going into the freeze's first..this should get good..lol.

 

[Battenkiller]

You have to calculate from absolute zero if calculating a % increase/decrease in temperature.

True, but we're not so much concerned with percentage of difference in absolute temperature as in the heat necessary to raise it. Only about 6% of the total heat needed to raise the wood to ignition temp would be needed for those few degrees between outside and inside temps.

The heat loss from melting the ice is significant, but still less than 15% of the heat loss due to evaporation of the same amount of water. Roughly, one BTU needed to raise every pound of water one degree Fahrenheit, 140 BTU to melt a pound of ice, 970 BTU to evaporate a pound of water.

The specific heat of wood is about half that of water, so it only takes about 0.5 BTU to raise a pound of wood 1°F. That means a 5 lb split that is 20% water would have 4 lbs of wood fiber.

Auto ignition temp of dry wood is about 550°F, so it would take 1245 BTU to raise one pound of water to boiling point from a 75°F ambient temperature, and 1900 BTU to get the wood up to 550°, or 3145 BTU total. Add an extra 75 BTU for water and 150 BTU for the wood and you can raise that same split from 0°F to 75°F. That comes out to 3370 BTU... a whopping 1% difference.

Of course, as mentioned above, you only need to get the outside hot enough to ignite, so I say drop in in there at 0° or at 75°. As long as the wood is dry on the outside it should ignite just about as quickly... unless you snuff the kindling fire out by adding too big a load too soon.

 

[f3cbboy]

You have to calculate from absolute zero if calculating a % increase/decrease in temperature.

True, but we're not so much concerned with percentage of difference in absolute temperature as in the heat necessary to raise it. Only about 6% of the total heat needed to raise the wood to ignition temp would be needed for those few degrees between outside and inside temps.

The heat loss from melting the ice is significant, but still less than 15% of the heat loss due to evaporation of the same amount of water. Roughly, one BTU needed to raise every pound of water one degree Fahrenheit, 140 BTU to melt a pound of ice, 970 BTU to evaporate a pound of water.

The specific heat of wood is about half that of water, so it only takes about 0.5 BTU to raise a pound of wood 1°F. That means a 5 lb split that is 20% water would have 4 lbs of wood fiber.

Auto ignition temp of dry wood is about 550°F, so it would take 1245 BTU to raise one pound of water to boiling point from a 75°F ambient temperature, and 1900 BTU to get the wood up to 550°, or 3145 BTU total. Add an extra 75 BTU for water and 150 BTU for the wood and you can raise that same split from 0°F to 75°F. That comes out to 3370 BTU... a whopping 1% difference.

Of course, as mentioned above, you only need to get the outside hot enough to ignite, so I say drop in in there at 0° or at 75°. As long as the wood is dry on the outside it should ignite just about as quickly... unless you snuff the kindling fire out by adding too big a load too soon.

battenkiller you never disappoint!!

 

[mecreature]

You have to calculate from absolute zero if calculating a % increase/decrease in temperature.

True, but we're not so much concerned with percentage of difference in absolute temperature as in the heat necessary to raise it. Only about 6% of the total heat needed to raise the wood to ignition temp would be needed for those few degrees between outside and inside temps.

The heat loss from melting the ice is significant, but still less than 15% of the heat loss due to evaporation of the same amount of water. Roughly, one BTU needed to raise every pound of water one degree Fahrenheit, 140 BTU to melt a pound of ice, 970 BTU to evaporate a pound of water.

The specific heat of wood is about half that of water, so it only takes about 0.5 BTU to raise a pound of wood 1°F. That means a 5 lb split that is 20% water would have 4 lbs of wood fiber.

Auto ignition temp of dry wood is about 550°F, so it would take 1245 BTU to raise one pound of water to boiling point from a 75°F ambient temperature, and 1900 BTU to get the wood up to 550°, or 3145 BTU total. Add an extra 75 BTU for water and 150 BTU for the wood and you can raise that same split from 0°F to 75°F. That comes out to 3370 BTU... a whopping 1% difference.

Of course, as mentioned above, you only need to get the outside hot enough to ignite, so I say drop in in there at 0° or at 75°. As long as the wood is dry on the outside it should ignite just about as quickly... unless you snuff the kindling fire out by adding too big a load too soon.

battenkiller you never disappoint!!

+1

all I know is its harder then hell to get some cold cold hickory to spark up on a cold stove.
I bet it gives a super cedar or what ever a run for its money.

throw it on a hot hot bed of coals and enjoy...

I like warmer splits but who has the room inside.


I would also like to know how to work time into this.

 

[seeyal8r]

I keep a weeks worth or so in the stove room.

+1.

I have 2 stacks I keep ready to go in the house and one outside the house with a tarp over it. All my wood is at the back of my property. Its like an assembly line.

 

[Dakotas Dad]

You have to calculate from absolute zero if calculating a % increase/decrease in temperature.

True, but we're not so much concerned with percentage of difference in absolute temperature as in the heat necessary to raise it. Only about 6% of the total heat needed to raise the wood to ignition temp would be needed for those few degrees between outside and inside temps.

The heat loss from melting the ice is significant, but still less than 15% of the heat loss due to evaporation of the same amount of water. Roughly, one BTU needed to raise every pound of water one degree Fahrenheit, 140 BTU to melt a pound of ice, 970 BTU to evaporate a pound of water.

The specific heat of wood is about half that of water, so it only takes about 0.5 BTU to raise a pound of wood 1°F. That means a 5 lb split that is 20% water would have 4 lbs of wood fiber.

Auto ignition temp of dry wood is about 550°F, so it would take 1245 BTU to raise one pound of water to boiling point from a 75°F ambient temperature, and 1900 BTU to get the wood up to 550°, or 3145 BTU total. Add an extra 75 BTU for water and 150 BTU for the wood and you can raise that same split from 0°F to 75°F. That comes out to 3370 BTU... a whopping 1% difference.

Of course, as mentioned above, you only need to get the outside hot enough to ignite, so I say drop in in there at 0° or at 75°. As long as the wood is dry on the outside it should ignite just about as quickly... unless you snuff the kindling fire out by adding too big a load too soon.

Is it summer already?

 

[snowleopard]

Okay, no one else gave you a hard time about this, so I get to. I have to admit, I grinned when I read that wood at 30 degrees ABOVE zero was sucking the heat out of your house. :lol:

That having been said, I do not bring wood in from the cold and put it directly in the stove. I pre-warm it inside. I do not use a tub or woodbox because it would take much longer to get warm and dry if the air couldn't move around it.

I have a rack that is 2x3 that allows for air circulation on all sides and underneath. It holds about three cargo-sled loads, and I put about two cargo-sled loads of birch between one end of the rack and the wall. At -40, this wood supply gets me from weekend to weekend. Before I reload, I pull the last of the warm, dry stuff and stack it in a box separate from the rest, and burn that over the next 24 hours or so, while the cold wood warms up and dries any surface moisture out. And right next to the back door, I have a tub that I fill with kindling and short ends that I want to have warmer before I burn.

And yes, I have surface moisture, because when I bring wood in that is 100 degrees colder than the house, it tends to get a little condensation on it. And yes, it's cold. If it's around -25 or colder, I can feel the cold coming off of the wood sufficient that I have been known to move after sitting down next to the wood rack. Just as the stove radiates heat, the wood radiates cold. (But not if it's thirty degrees ABOVE zero when I bring it in.) We're talking a substantial amount of wood here, and the tradeoff is still worth it in terms of BTU's lost by warming it up inside. Note: I store this in the sun-room, and I have many plants in there. They don't seem to suffer from the cold or the bugs.

Everyone's bug situation is different, but I have not seen insect activity as a result of keeping wood inside.

 

[gpcollen1]

Wood needs to come up to temp to be combusted right? So only makes sense that if you have a small fire that is not that hot, it will take a bit to get the wood to light. Make your small kindling fires a bit bigger and give it a go. should not be a problem then. Other than that, split your wood a bit smaller and then add it to your small kindling fires. Should light up a bit quicker. Shoot, my kindling is split up splits anyway = good seasoned kindling.

 

[f3cbboy]

Just for the record, i have never once preheated a piece of wood before placing it any stove of any kind. After being a member of this forum for a little while now, i often wonder what people are thinking when they put a piece of wood in the stove. my brain is too small to think beyond " I hope this burns and warms the house".

 

[Jags]

my brain is too small to think beyond " I hope this burns and warms the house".

Nope - you pretty much "nailed it" for me. :lol:

 

[Adios Pantalones]

The difference in temperature RISE is what is needed to get around absolute temp use. That is the ignition temp minus the wood temp. Heat is lost through through sublimation, evaporation, and heat of fusion, specific heat of the water, specific heat of the wood in the layer that ignites.

Further losses occur through the mass of the wood in the process (despite wood's insulating properties) through specific heat of wood and water, and heat of fusion in melting ice.

You cannot actually do the math without some crazy measurements of the temperature profile through the piece. It'll be a gradient rather than a straight difference, so fire up them diffEQ's

I have plenty of wood that's "dry", but the outside is a bit wetter under the bark etc. I don't need any math to tell me wood that's got water ON it is harder to get going. Plus- I'm a chemist in my day job so I'd rather not do all the math when it's not effecting my pay check

 

[firefighterjake]

I've never noticed a difference with cold wood vs. warm wood . . .