For serious wood burning, the insulated firebox offers design flexibility, high efficiency, fast starting, long burning, and fault tolerance. Unfortunately, it produces beautifully -dazzling fire conditions which are too hot for large ceramic glass "windows". Picture below was taken with a large window that did not last long. This firebox was built to replace my Vortex Flame Amplifier, (burner/ firebox) which was researched in the 1980's. To better see high temperature fire quality, click on the picture:

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Insulating arched firebrick were used primarily along with some other features. Refractory anchors were used as "bumpers" to protect the fragile insulating firebrick. Anchors are very dense and strong firebrick which have somewhat corrugated faces, (made to anchor rammed refractory mixes).

Despite the best refractory ratings, high fire temperatures weaken any common industrial material. Loading large firewood chunks can damage even the stronger anchors. Keeping new wood centered in the coal bed can cushion the furnace walls and avoid breakage.

The picture above shows the anchors and insulating firebrick "risers", (vertical walls upon which the arch will sit). To accommodate the existing conditions, the layout had to make an angled turn. This firebox is built next to a large composite flue core, which had been built in the late 1970s. (It was improvised from traditional masonry heaters, except cast in place concrete methods were used instead of traditional bricks. Circular patterns were molded, similar to the core on this linked page. A versatile cement branded "Fondu" was used internally and Portland concrete externally, with 3 concentric flues. More pics may be added here from old 35mm film).

Heavy rebar framework was welded in place and also sunk into the old core. Frankly I prefer not to build this way. This was a fast job as winter arrives and I actually should have spent more time to do the whole remodeling effort more in this manner. (Linkked Page). A wood- loading door was salvaged from a junked Ashley wood stove and it was welded to the rebar.

The arch is started above. To the bottom of picture on right is the passage to the bottom of the heater core.  To the bottom of picture is the threshold of the arch seen in first picture. Because the ceramic glass of today is not capable of withstanding high temperatures, a temporary insulating panel is presently used, instead.

Temporary ferrocement shell panels were attached to the thick rebar and loose mineral wool was packed in between. Time passed before a cooking surface was put in. Finally a simple plate of cheap 12 gauge steel was used. It was bent into a very slight curve to prevent uneven warping. This thin steel was chosen for faster conduction.

A small damper was added to it for more control.  Fabricated, insulating board was used to build a fast oven and door.  The 12 gauge steel transfers heat very well. Water boils well, though slower than "High" on a common cooking range. The best part is the reflection intensity of insulating refractories. I can bake bread rolls instantly without burning.

All in all the general configuration works well.

(Page is still under construction)

An obsolete "AP Green, Refractory Pocket Catalog" offered insulated chambers to improve ordinary oil burners:

For retro-fits and low cost experimentation, insulating blankets can be used. While plain blankets can hold up well in some applications, I also like to apply a slurry of (phosphate bonding) mortar, which can soak into the mineral wool to firm up the wool faces. I have had great results with a brand of refractory wool called Fiberfrax, though others may work as well. Using thin blankets of this material in a laminated fashion, soaking each face in a reractory mortar slurry, might produce a good firebox body of any shape or size. One could make a "paper mache" or "papercrete" form for the firebox. Once firm and dry, the form work could simply be covered with slurry-laminated wool blankets, (providing all materials are refractory products). The paper form could burn out, but slow initial heating and drying should be practiced. After the structure has been slowly dried and fired, it will be permanently set and ready for normal (and careful) use.

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