How do you figure the BTU rating based on the fire box size?

[Richardin52]

I’m talking about a conventional wood furnace. For instance how much heat would I get out of a furnace with a 24" long 14" wide and 20" high fire box? Is there a formula I can use?

 

[shoeboxlen]

btu would depend on the wood your using draft how dry it is and probably a hundred other factors I would think.

 

[laynes69]

Thats almost a 4 cu ft firebox. Efficiency plays a huge part of the heat output. A conventional furnace maybe 80,000 btus. This is taken from different manufacturers. You get into a EPA certified furnace like mine and its rated around 140,000 btus with a 3.5 cu ft firebox. Basic wood furnaces aren't all that efficient. Seems like a small firebox for a standard furnace.

 

[TCaldwell]

fire box size and boiler output do not have anything in common, output is based on the effiency of the boiler design, i guess you could approximate that x cuft. firebox will hold x lbs of wood at x btus/lb and come up with a gross btu value for a fire box load of wood, but it is up to the effiency of the boiler to determine,1 combustion effiency and 2, the ability for the boiler absorb and transfer that heat to your distribution system. If i recall nofo calculated a boiler effiency in the mid 80% and system effiency under 60%

 

[DaveBP]

You're asking how you can determine the HP rating of an engine based on the size of the gas tank.

As everyone has responded, too many variables to put a meaningful number on it. There may be a correlation but no real formula.

Check out this fire box:

http://www.herlt-holzheizung.de/engl/HSVE.html