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[mtneer]

Hello all, I’m new to the site……and so glad to have came across it!  I currently heat my old farm house with wood but i would like to keep the mess outside.  I’ve been tossing around the idea of making an outdoor forced air wood furnace.  I can’t see dropping over 1500 bucks on a “lil house heater” that I can build myself.   I’m pretty good with a welder, but engineer I am not!  I have a laundry list of questions that I hope you all can help me with:
1 How thick should my firebox be?   I was thinking of a cylindral firebox, if so, will I still need to line the bottom with firebrick?
2 How much space should I leave between my firebox and the outer chamber?   How thick should the outer chamber metal be?
3 What type of insulation should I use to cover the outer chamber.
4 Is insulated flex duct hose safe to use for the hot air line running to the huose?  I have 3 pieces of 10’’ plastic culvert on hand.  I was thinking that I could run the flex duct thru it and bury it underground.

Thanks in advance!    Brent

[peacmar]

Before I answer your questions let me ask this, why forced air? You will waste lots of heat and burn unnecessary amounts of fire wood. You will need very very high temp insulation at key locations and a very large surface area to transfer all the heat you will need. Underground air ducts have a potential to grow mold being a dark and damp environment. During the summer months you could be growing a very toxic mixture in there. If cost is a factor please elaborate on your areas of concern, there are enough creative individuals around here to brainstorm some nontraditional ideas.