hi Bruce,
since you are a fellow "Ontarian", did you get snow last night? i got over an inch of snow here where i live last night! good thing your RMH is working.
if i had a nice mass like that, i would probably like it to be maintained around 90-95 F if possible, but im sure temps would drop eventually when not in use. i sure would not want it to drop below room temperature, but i guess that is obvious. i would guess it would be nice to have the mass between 75-95F, but if youre cold, and if the mass is in a safe fire-proof area, lets say cement floor and brick walls, im sure if could go even hotter than 100F in a safe place away from combustables.
im curious, do you often sit on the mass? does it get too hot or uncomforftable? how is the radiation from the bell? what size (diameter) is your final exhaust? is there steel in the burn chamber flame path? i cannot remember from your last thread