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 Bandera, NB Black Diamond, Home Built Offset, Vision Classic Kamado, Green Mountain Daniel Boone, Weber Gasser, Smokey Mountain Cabinet, and several Weber kettles of various sizes.