I dont' know about Karl, but I have my thermostat set to 40F. Sounds
really cold, but I typically work out in my shop in a long sleeve shirt
quite comfortably. With the warm floor, your feet don't get cold.
This is a big factor.

I am using an electric water heater on off-peak power (~$0.03/kwh). My
heating bill is only an extra $50 or so a month.

I am heating a 40x48 shop w/ 16' sidewalls. I insulated the heck out
of it. There is nearly 18" of cellulose in the ceiling. The walls are
ICF. An effective R factor of 50.

I have considered adding a corn boiler for a primary system, but am
having a hard time justifying given the above stated results to date.