firewood weight

[west penn]

 I looked in the tool box and found the weight of a cord of oak but am wondering if that number is for green wood? Any one know the approx weight of a cord of seasoned firewood?I know there are a lot of variables, but I'm trying convert btu's in the 12 cords of wood that I burn to see how much hard coal it would take to heat the same area. Sorry if i'm not in the right area.

[SwampDonkey]

Yes those are green weights west penn. If you have a moisture meter you can test some samples of each species in your firewood and use the empirical data for green weight in the toolbox and subtract to weight of water (62.4 lb/ft³) by % it dried. To do that you have to find out what oak weighs bone dry. We have empirical data that shows green oak has a specific gravity of 0.58 (average between red and white oak).

                           water 
Oven dry weight = 62.4 lb/ft³ x specific gravity green
                       = 62.4 x 0.59 = 36.8 lb/ft³

For instance if green oak has dried to 20% then:

20% MC oak= Oven dried x (1+ MC%/100)
                    = 36.8 x 1.2
                    = 44 lb/ft³

[Al_Smith]

For a simple rule of thump use 2 tons per cord .Most hard woods will fall in between 3400 and a tad over 4000 per cord .

[Ron Wenrich]

Rule of thumb is one cord of wood = one ton of coal = 100 gal of oil, if memory serves me. 

[Al_Smith]

Yeah that's about right if you are using higher BTU wood such as oak or hickory .If you factor in not so good of stuff like basswood or cottonwood you about have to double it .BTU per pound figuring 20 percent moisture in wood is about the same just the cordage figure because of the weight changes .

[Raider Bill]

Are you talking a cord or a face cord/rick?

[west penn]

   I'm using about 12 full cords to heat the big old farm house I live in although a good portion of that is slab wood. I haven't used the oil furnace for years but since my wife is havig back problems and I'm not home all day, I was considering  a dual oil ,coal furnace with a stoker and selling the slabs, etc to offset the price of coal or oil. I read that a pound of oak has about 5000 btu's and a pound of hard coal has 14000 btu's. So with a more efficient furnace I would be looking at around 9 ton if I did the math right.    Just thinking out loud right now.

[Kansas]

If I remember right, we have a chart posted at work, or at least did have, of the BTU's of various types of firewood. This was put out by I believe the Kansas Forest Service but the numbers may have come from someone else. They had a brochure on it. We had some around but don't know if they are all gone. I can take a look today.

[Raider Bill]

I never seem to know if when talking firewood if someones talking face cords or cords.

Here is a chart I found about BTU's

http://www.consumerenergycenter.org/home/heating_cooling/firewood.html

[Al_Smith]

There a bunch of charts on the net to convert from about any source of heat to another .There's even charts which compair  fossil fuels to heat pumps weather they be air to air or geothermal .

While it's nice to know you also need to factor in heat loss per hour depending on the structure to get an aproximation of heating requirements . My house,well insulated brick is right at 30,000 btu per hour BTW .

[John Mc]

A lot of the charts on the net are not all that great. Folks compile them from a number of different sources, and don't correct them all to similar moisture content, so the weights can tend to be all over the place. Since many charts just use uncorrected weight to calculate BTUs (BTUs per pound of dry wood are all VERY similar), rather than some actual BTU measurement, the heat content gets thrown off as well.

I've attached a chart of BTUs by species where the author went to some effort to correct them all to similar moisture content (I exchanged emails with the author, but forget the actual MC he used. I'm sure it was somewhere in the 15-20% range, however). This chart is posted with the author's permission, as long as it is unmodified, and retains the company name, copyright, and web link info.

John Mc

[Raider Bill]

I've seen that one before. Seems much more inclusive. Thanks!

[John Mc]

They updated it fairly recently, correcting some errors (I got into a conversation with the author when i first asked permission to post it here ... last spring, I think).

[beenthere]

There are many variables in getting the weight per cord. Wood from trees will vary in specific gravity, as well as the moisture content, both between trees as well as within a tree.
Then a cord of wood will vary a lot depending on how it is split, as well as how it is stacked (not forgetting how it is measured ). Unless all the variables are controlled but one, then the answer is just a good estimate at best.
Relative differences between species is helpful to know.

[SwampDonkey]

I have a 200 gallon oil tank, and I can guarantee you if you want to be comfortable in this old house 1 cord of firewood will last as long as 200 gallons of oil. It would cost you a fortune to use oil these days in eastern Canada. Just ask any old timer on Canada pension how much will be left to buy food for the fridge after the oil tank gets filled. ;) right now it would cost over $1000 to fill the tank. Meanwhile $1900 got me all the firewood I need for the house and the shop 9 cords. Where do you get cheap coal? They closed up all the coal mines up here, one mine had one remaining customer, the power company. They are going to close up the coal fired generator(s), so the mine was closed up.

[Al_Smith]

Aha you really don't cut wood with that souped up weed wacker .You buy the stuff .Geeze and you thought I was a week end warrier .Week ends and during the week I'll have you know . 8)

[SwampDonkey]

Firewood guys have to make a living to.  ;D Besides, I got lots of stuff to do. 

I'd like to strap that 550 on your carcass for a 40 hr week and see where you spend your weekend.  :D :D

[Al_Smith]

40 hours in the same week  Geeze I wouldn't  get 40 hours behind a wacker in ten years .

[SwampDonkey]

'nuff said. :D Only don't think it's easy ground like the end of your lawn. Take the saw and walk in threw blow down, rocks, spring holes, hummocks and all around wood debris under foot, plus in bigger wood it ain't designed to cut that the boss man likes to push the perimeter into.  :D

Oh, as to my numbers up there, they are from empirical data as are the methods to calculate. Just to get ball park figures as we say. Everyone surely knows that every stick of green maple is not the same through and through or any other species. You have to work on averages when your dealing with nature. The wood handbook has the methods and figures explained, not neat and concisely maybe, but they are there. (Page 3-12 methods one and two for the math, and table 4-3b for data figures). I just pull out my Wood Tech book which has a nice table all presented and I believe the forum toolbox figures were pulled from there to, since I know RonW has stated so. As far as the BTU's I don't have those, but I thought the first question was asking if the figures in the toolbox were for green and I answered that along with a way to "estimate" partial drying. There is a graph in the Wood Handbook that all you need is to intercept sp gravity, and MC of any wood species and your in the ball park for weight at that MC (Table 3-7b). Of course that presupposes you know the spec gravity at that MC because it changes with moisture content by definition.

[Al_Smith]

Well some of it looses a lot of weight when it's dry and some seem to loose very little . Oak for one just seems heavy no matter what .

Tulip poplar,basswood and some of the lesser firewoods are heavy as lead when green and like balsa dry .Maple at least to me seems to me to loose weight .Cherry looses weight but gets hard as a rock .Osage orange gets so darned hard it will cause sparks to fly off the chainsaw chain .

[SwampDonkey]

I find red maple lightens up a lot when drying, but I don't use that as traditional stove wood. It won't even get my steam chest hot enough. Beech, rock maple and yellow birch are heavy green or dry it seems when you handle 9 cords 3 times before you get it to the stove and in the ash pale on the way out. :D We rarely see oak as firewood up here and it's not really managed because it's so inconsequential as to availability. When you travel for instance from Houltan Maine, southward on the I95, you don't see much red oak until you hit Bangor. White oak isn't that prevalent until New Hampshire. That is where I got the only white oak from in my yard, that is the only one for miles except for the towns have English white oak and maybe a bur oak. Bur oak does grow here in the wild, but rare and mostly in Grand Lake area, just an odd ball that is separated from the rest of the range by 100's of miles. If you cut red oak down that has survived in our maple forest, you pretty much wipe it out unless it's a clearcut. Mature sugar maple, yellow birch and beech will win as a climax forest because of shade tolerance.

[Al_Smith]

Well yeah what's available is just the difference in geography .

The beech here are huge same with the oaks .Nobody cuts them down for firewood though unless they are hazards because of a storm or  just dead for whatever reason .

The ash all got killed off by that danged EAB thing .Some of them are as big as oaks .Something else is getting to the hickorys also . I've got several 80 to 100 footers in the adjacent woods that are dead standing . Fact between the ash and hickorys plus a big dead white oak I'll be lucky to get them all down by the time the snow flies .

The trick is not dropping them because gravity will do that .The secret is not tearing up everything around them in doing so .Some of them are going to have to be snaked out with a cable and a bulldozer . I have both just not the time to do it  in a timely manner

It's one thing talk about weight of firewood you move one piece at a time and entirely a horse of a different color with a 20 foot log that might weigh 3.5 tons .Most I'd guess would be a ton and a half maybe two so that won't be a problem .