Let's do some math.

I'm still trying to estimate how much wood i'm going to use this year. I looked at my gas bill from last year and I used 70 MCF of gas. I know that's not alot, but I kept my house at 60° except for the two rooms I heated with the space heater. 1MCF is a thousand cubic feet. I got that from the back of my gas bill. So I went online searching for BTU output of different types of wood. I found two charts. Let's use red oak for the calculations. Chimneysweeponline's chart says red oak has 24 million BTUs per cord. They define a cord as 85 cubic feet at 20% moisture. They take out 43 cubic from the cord as air space between the logs. Daviddarling's site has red oak as 24 million BTUs or 16.8 milllion recoverable. 16.8 million is 70% of 24 million. Am I correct in assuming he is counting recoverable as the amount of heat you get out of a 70% efficient stove? Anyway, my furnace is 45 years old and it was only 80% efficient to begin with and I doubt if it's that high now, plus I know I loose alot of heat from the uninsulated duct work that runs throught the unheated basement and crawl space. So my summit is 72.5% efficient and I'm guessing that's better than what I'm getting from my furnace. So let's go with the 24 million BTU number unless any of you on here disagree with it.

http://www.daviddarling.info/encyclopedia/W/AE_wood_heat_value_BTU.html

http://www.chimneysweeponline.com/howood.htm


From looking online I came up with the BTU output of natural gas as being 1000 BTUs a cubic foot from one site and 1,031,000 BTUs from 1 MCF from another. So check my math here.


24 million divided by 1,031,000 = 23.78 MCF in a cord of red oak. Is this right?

70 MCF divided by 23.78 = 2.94 cords of wood to keep my house the same temperature as last year. Does this sound right?

I realize I'm going to be keeping the whole house warmer this year than last year, because I'm not going to be closing off two rooms and heating them with a space heater. I'm just trying to judge how much wood I will actually go through and I know I will still use the furnace some. My goal is to keep the house warmer, like 70° instead of 60° and still spend less on natural gas. I'm going to do some insluating this year as well but that's another thread.

Is my math correct and am I using the correct figures?

BeGreen he defined it as a stack 4x4x8 which is 128 cubic feet but with air gaps so he is going with 85 cubic feet of solid wood. That makes sense to me.

I don't understand your statement : "you about a mil seven per cord"

As for stove efficiency. That shouldn't come into play. I'm measure gas I bought from the gas company against wood stacked outback. The furnace is 80% and the stove is 72.5%. Plus the furnace is 45 years old. I doubt I'm getting 80% out of it now, and if I am I'm still sending 20% into the basement and crawl space. So honestly I think the stove will be more efficient. I do realize the it burns all the time thing. I should have 5 cords done pretty soon. Not all of it is good hardwood and It' probably won't be completely dry by this fall.

Goose,

That's what I'm doing. The problem is i'm about out of time for wood that will be dry enough to burn this year. I'm going to keep cutting and stacking all summer and fall. I'm even thinking about getting a load of slab wood. The local mill sells it for about a hundred bucks a dump truck load delivered and it's already cut to size. I can assure you that next year I will either have plenty of wood or I'll be selling a one year old insert on here. I will 5 cords cut and split by the end of the week. The rest I scrounge will be for next year.