Brick Oven Insulation: How Much?

If there is one problem that can be avoided easily in the construction of a brick oven, it is heat retention.

Part of this depends on MASS: the masonry that will hold whatever BTU gets thrown at it.

The other (the easy one) is insulation.

Two words: Over-insulate... okay that's almost one word.

My brick oven and the ones I build or consult on are super-insulated because there's nothing I like (aside from fresh bread, fresh pizza, fall apples, a climb up a mountain in 60 degree sunshine...) better than knowing and hearing that an oven I built stayed hot for days.

The current oven in Ventura, CA has 6" of insulation placed as shown.  4" of Foamglas solid insulation is under the floor and insulating refractory concrete is pour around the base and chimney.  The goal is for very little heat to escape. 
Doing all this before you close up the structure saves the disappointment of having an oven that won't get or stay hot.

More recently I have come to understand the value of ceramic fiber insulation (brand-named Fiberfax).  Layers of one or two inch sheets laid over the dome and placed around the chimney assure me and the owners that there is a fireproof envelope around that hot dome of bricks.

Caution: The stuff is flaky and requires a mask and gloves for safety.