lsayre wrote:Agreed! Then perhaps the question should be, how well does 200 times the grate area equate to a hand fired stoves BTU's?

It works a lot better but it still is a starting point for a stoves design. The extent of heat exchange area as well as how efficiently that heat exchange works effects the size and efficiency of the stove. Tending intervals at a given Btu output will also govern the size of the fire pot as well as the grate area. If you want a stove to burn 100,000 Btu of coal and tend it every 12 hours then that's about 10 pounds per hour or 120 pounds in 12 hours. There still has to be burning coal left to ignite the new charge so the fire pot would have to hold about 180 pounds if you wanted to keep 12 hour tending times. That's why those old central heating furnaces and boilers were so big. The ratings on new stoves are what can be achieved burning flat out for a few hours.

The best measure of a stoves heat output is still size. The square feet of heat exchange surface which will emit a given amount of Btu at a certain temperature provided that temperature is reasonable. From 400 to 600 it more than doubles but to maintain 600 degrees as an average on the entire stove is not practical.

Temperature of Surface Fairenhiet -------------- Total Energy Transferred 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.