How to compute Stove output BTU ?

Is this the right way to calculate stove output in BTUs ?

I loaded the stove with(14 splits) 83.8 lbs of 3 year seasoned birch
12% moisture (resinous wood & bark) 8600 BTU/lb (est)
83.8 X 8600 =
720,680 BTU in the stove
Stove is 82% efficient
720,680 X .82 = 590957

590,957 BTUs of usable heat in the house when the wood is gone.

If I get a hour burn, that's roughly 40,000 BTU per hour ?

15°f, 4 mph wind, 87% humidity, dew point 12°f

 

Doing some checking, I found this..http://www.naturalresources.umd.edu/Publications/PDFs/FS926WoodFuel.pdf, and used 7,000btu/lb for Oak.
My stove is less efficient than yours by probably 1/2.
I came up with a yearly need of 126,000,000 btu. Presuming 5 cord/yr., and also presuming all Oak (and nowadays it's actually about 1/2 Oak).
It can get very detailed very quick. I've done this in the past and came up with a similar #.

 

Very good info. I'm sure there's some unforeseen losses not accounted for in the process too. I'd calculate it around 80%. I'm in Erie this weekend but I'll do some calculations of my own when I get home

 

Dave I would say that is pretty close to correct. I have tested multiple weighed loads vs calculated heat loss vs tested loss in my house and every which way comes in between 6,000-6,500 BTU per pound of wood heat output. So I would suspect somewhere in the 6,500-7,000 BTU per pound range to be correct with your stove.

 

Coming up with accurate BTU numbers is tough.
Have found numbers from 7600 to 9700 BTUs
Per pound, resinous wood.
Tough to get a good BTU per pound # for my birch.
The drier the wood, the more BTU per pound, so a good % moisture #
is needed too.
May call me the AK forestry dept next week.


80% probably a better efficiency number
With a 1-1/2 old cat combustor, new BK 1107 stove # is 82.5%.

Am impressed with the 3 year seasoned birch.
Lights fast, gets up to temp fast, burns down good,
& on low burns , it burn clean & long with good heat output.

 

With your softer wood, what are the max burn times you get from the King? 30?

 

Shoulder season, 30 to 36 hours of heat.
2 days with hot coals and the stove warm .

Now hanging around 20°,
16 to 18 hrs, then a few splits to get thru until 10/11pm for a new full load

The one I just weighed went 17 hrs, still lot of
Charcoal & heat , added 2 splits & got to 1030 tonight

 

Dave, would a 12 hour schedule work for you?

 

17 hour burn would be an average of right around 35,000 BTU's per hour usable.

 

I think output numbers are overstated. Before I replaced my exterior walls in the room that the stove is in, I had baseboard electric resistance heat of about 40K btu/hr. IMO and hardly scientific, there is no way the King does that on average over a burn cycle.

 

Could make several schedules work.
Any thing over about 10 hours.
After 17 hours, rake the coals, throw on a few splits, good until the night loading.

I like the full load & not have to mess with it but one time where I rake the coals,
then decide how much I need to throw in to get a good burn down, heat & get to 10 PM.

But I could add less wood & get shorter burns. Might try it when the weather is a bit a warmer.
15°f now. House 73°. (12-1/2 hours into the burn) to warm for me, good for everyone else.

Still learning & the weather don't like to stay consistent.
Weather man has been off by about 10°, they said 4° for last night, was 14°

Gotta go outside & plow , cool down a bit. It's hot in here LOL

Light, dry fluffy snow:

 

To be -2°f tonight.
Shorter, Hotter burn, higher BTU output.
May try to weigh another load tonight.

 

84.7 lbs for tonight's load at 9:15
Cat up to temp @ 9:30 PM,
Blower 50%, stat on 2.4 (my setting for OAT of zero°)
11° now, forecast to go to -4°f,
house 74°, to warm

Load:

 

9:30 AM. 12 hour burn & still cranking out good heat.
OAT -3° f, house 73°
Estimate 4 more hours of heat from what's left in the stove.

Fun when a plan works, weather forecast -4°, got -3.
Stove setting perfect





Few hours before the sun comes over the mts
Daylight, cold crisp air, calm, -3

 

Stove heat output just dropped off to where it won't keep up at -2°, 11:15 AM

Raked coals forward, added a split to burn down the medium amount of coals & keep heat cranking.
Near 14 hours of good heat.
OAT -2°f, house 72°

Sun will be over the mts soon. Hope it gets above Zero

 

Sun just now hitting the tops of the trees

Stove back to cranking

Still -2°f, My oven can heat an insulated house with 40°f OATs

 

Whats OATS....Sorry dummy here...

 

OATs, Outside Air Temperatures

Read or heard it somewhere & thought it was funny

Was something like "at 40° my oven will heat my house"
Still think it's funny, Alaska humor.

Above 40° at night who runs their stove ?
40s our summer temps when it's dark. Solar gain & cooking overcomes that pretty easy.

 

Got up to 2.4° f OAT , then started getting cloudy / foggy

2250 sq ft house at 73°. Stove heated space.
Added 21.2 lbs of splits (3) to the stove.
Little over 104 lbs so far.

NG heater in the garage set for 40° )

 

I have built a small fire with overnight lows as high as mid 50'sF. No solar gain for my house. The oven would do it but I'm not going to use it to heat with.