Maintain those temps, boys

[Marshy]

Here's a picture from the modification build... it should give some idea of the "firebox" size (the open area in which the fire burns).
It like a 55 gallon barrel... but it's a furnace, not a stove.
Firebox "size" has nothing to do with fuel capacity... it's about heat transfer surface area. When the computation air kicksbon does it pressurize the firebox or the ash pan area?

How far down from the door opening is the greate? Does the combustion air from the fab enter above or belt the greate?

 

[Whitespider]

Do you have a baffle in the top of the firebox beforeb it enters the flue?
How far down from the door opening is the greate? Does the combustion air from the fab enter above or belt the greate?

Yes, there's a sliding baffle... the top lever is used to slide it.
The top surface of the grate is about 9-10 inches below the bottom of the door opening.
Combustion air enters the unit above the grate, but there's an angled, welded channel (or plate) that directs all of it under the grate.
Kind'a like this...



You can see in around the opening for the baffle lever, and when the draft blower is running the area above the baffle is a regular firestorm... it's burning the smoke, without any added secondary air, just heat.
DAKA calls it a "secondary heat chamber".
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