Adding masonry to increase wood stove efficiency By adding masonry and mud to an old cast-iron wood stove, I greatly increased its efficiency -- and it even has an oven! (note the wooden door on the right, just above the iron stove door). The wood that used to over-heat me, briefly, in the morning, now keeps me comfortably warm all day, and into the next morning (depending on how long I fire it and how cold it is). And, unlike most iron stoves, it no longer generates that fierce, dry heat that you can only moderate by burning wet wood, or by damping the fire down to a messy, smoldering . . .
the upside down fire
You can greatly improve how your oven performs by how you lay and manage the fire. Here's how and why I build what Pat Manley calls "an upside down fire." (Follow the link to an overlong video version). The first principle of fire requires applying to heat to fuel. When the fuel gets hot enough, it bursts into flame. But if you pile many pounds of wood on top of your kindling, it will take a long time before all your fuel can really start burning. Meanwhile, you'll get a lot of smoke in your (and possibly your neighbors') eyes, and you'll lose a lot of fuel (all that smoke counts as unburnt . . .
The Cob Oven FAQ
Q: what's the difference between a cob oven and an earth oven? A: Usually, they mean the same thing, but sometimes when people say earth oven, they mean a simple pit oven, like a Fijian lovo or Samoan 'umu. Q: How efficient are cob ovens? A: There are two things to consider here. First, since you have to heat up the whole mass of a retained heat oven in order to bake, clearly, cooking just a few loaves of bread won't make efficient use of all your fuel. However, the more you cook, the more of the stored heat you use up, and the better your efficiency. Insulating an oven increases efficiency . . .