Here is a neat formula to use for obtaining a good idea of the Btu burning capability of a hand fired coal stove. Use the grate area, not the size of the firebox, fire pot, or fire brick.

GRATE AREA SQ.FT. x .65, THE PERCENTAGE OF EFFICIENCY x 8, THE POUNDS OF ANTHRACITE PER SQ.FT. x 12,500, THE AVERAGE BTU'S PER POUND OF ANTHRACITE.

Here is a calculation for you that will interest you. I showed this to Larry and he was amazed that it was so close to the actual laboratory test results. I got it from a book Solid-Fuel Furnaces and Boilers, by John W. Bartok, copyright 1982.

Grate Area (sq.ft.) X percentage of combustion efficiency X pounds per sq.ft. on grate X Btu output of fuel

The large Chubby has a grate area about 12" round. To get the sq.ft. of grate area, we take 12/2= 6, 6X6=36, 36X3.14=113.04 Sq.in, 113.04/12=9.42, 9.42/12=.785 sq.ft.

The percentage of combustion efficiency for most coal stoves is 65%, unless stated otherwise, 50% most wood stoves unless stated otherwise, the Chubby states between 85% to 90%.

The pounds of fuel per sq.ft. of grate per hour are: Anthracite Pea 5, Anthracite Nut 8, Hard Wood 20.

The Average heat output of fuel is: 12,500 Btu's for Anthracite and 6,500 Btu's for Wood.

Now that we have some definitions, lets do some calculations.

The large Chubby in the wide open damper, most heat up the chimney: .785 X .65 X 8 X 12,500 = 51,025 Btu's

The Large Chubby in the half open damper, .785 X .85 X 8 X 12,500 = 66,725 Btu's

The Large Chubby with the Damper mostly closed, .785 X .9 X 8 X 12,500 = 70,650 Btu's

So, Larry's figures are correct. This is a really neat formula that can be calculated for any stove. There are other numbers for different fuel types to run these calculations. The only thing is when trying to calculate other stoves, we can't assume just by closing the manual damper that the efficiency will go up. The efficiency ratings have been started to get published more by manufactures, especially now that the government tax credits for wood stoves have been instituted.

Okay, to answer your size question of the Jr. Chubby, it is 28" high with the legs, 14" round, 16" round on cast iron top, 23" to the top of the rear flue. I'm guessing that the weight is about 100Lbs. At least that is what it feels like to me.

Now let's run some numbers on the Jr. Chubby. The Jr. Chubby has a grate area around 8" round. That is .3489 sq.ft.

The Jr. Chubby in the wide open damper, most heat up the chimney: .3489 X .65 X 8 X 12,500 = 22,648.5 Btu's

The Jr. Chubby in the half open damper: .3489 X .85 X 8 X 12,500 = 29,656.5 Btu's

The Jr. Chubby with the Damper mostly closed: .3489 X .9 X 8 X 12,500 = 31,401 Btu's

There are other formulas to calculate the heat output of stoves too. Here is another one.

Re: Stove BTU output based on temp and surface area?

A chart from "The Wooburner's Encyclopedia,1976" says: The amount of heat emmited per square foot is dependent on the temperature of the radiating body.

Temperature of Surface Fairenhiet -------------- Total Energy Transfered BTU's per hour per foot

80* ------------------------------------------------------ 15 Btu's / Sq.Ft.

100* ------------------------------------------------------ 51 Btu's / Sq.Ft.

150* ------------------------------------------------------ 168 Btu's / Sq.Ft.

200* ------------------------------------------------------ 315 Btu's / Sq.Ft.

400* ------------------------------------------------------ 1230 Btu's / Sq.Ft.

600* ------------------------------------------------------ 2850 Btu's / Sq.Ft.

800* ------------------------------------------------------ 5430 Btu's / Sq.Ft.

1200* ----------------------------------------------------- 9370 Btu's / Sq.Ft.

This formula will get us close and usually assumes 50% to 65% efficiency stoves though. Here is an example for the Jr. Chubby:

The Circumference of a 14" round pipe is 43.98" X the height of the stove body, minus the legs, is 23" X the area of the 16" round cast iron top 201.06", then multiply the total in sq.ft. by the outside temperature of the stove.

So, 43.98 X 23 = 1011.54 + 201.06 = 1212.6"/12/12= 8.42 sq.ft. X let's say 600 degrees F 2850 Btu's = 23,999.37 Btu's

That's pretty close. Neat, huh?