Besides cob (and water) what is the best material / method for a heat mass battery?
I've a rsmh to heat my shop with.
Thinking of a concrete block "form" to hold pea gravel mass in place around the first 10' or so of 8" horizontal exhaust pipe exit flue.
I'll insulate behind and under the mass battery bed to keep the heat from dissipating into the wall and floor.
Pea gravel is not the most efficient heat sink I realize, but easy to remove when the time comes.