Is an insulated firebox really that much more efficient than uninsulated? I admit I can be a bit simple minded at times, but I just can't imagine it makes a considerable difference.
I can understand an insulated cooking chamber where you are trying to reach and maintain temps.
To me, it seems the heat is leaving the firebox at a rate determined by the dampers and would only be marginally effected by outside temps.
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Large UDS, Small UDS, CG Akorn, NB Offset, Home Built Offset, Vision Classic Kamado, Green Mountain Daniel Boone, Weber Gasser, Smokey Mountain Cabinet, and several Weber kettles of various sizes.