Build a High Efficiency Fireplace (90% Efficient!)
It's possible to build a high efficiency fireplace using cast clay for the firebox and sheet metal for the stovepipe.
The completed high efficiency fireplace will look something like this. Its convoluted stovepipe furnishes a quick blast of heat after the initial lighting.
PHOTO: BOB CHRISTENSEN
 Bob tacks more of the galvanized veneer to the upper half of the exterior form.  The completed casting frame prior to spooning in the Kast-Set. All the metal surfaces have been coated with oil or grease before the "mud" is laid in.
 After making a cardboard template, Bob Christensen outlines the borders of the modified Russian fireplace.  Alex Sanchez prepares to halve the wooden mold at its midriff.
 One week later, after the refractory clay has set, the forms can be removed.
 The inner and outer braced plywood forms ready for covering.  Alex finishes fastening a sheet-metal "skin" to the inner section of the mold.
 One part of the room oven's finished body, which must be damp-cured, then sun-dried for two or three weeks.