Is that 'electric furnace' a heat pump type or coil type?
It's a coil type.
I wish I had thought of this before. Now I can leave on all the lights and appliances I want.
Resistance electric heating (coil type) is very expensive to run. A heat pump uses about 1/3 the electricity for the same heat unless you are pretty far north. There are now window AC units with true heat pumps in them for under $1000. They may pay for themselves in one heating season.
"coil type" was still confusing to me. Made me think of heat pump compessor/evaporator coils.
To the OP:
if your heat is RESISTANCE heating (i.e. a wire has electricity flowing through it and gets hot which heats up your home) then yes your mining rig is just as efficient.
Resistance heating = 3412 BTU of thermal energy (heat) per 1 kWh electrical power used (and billed).
Mining Rig = 3412 BTU of thermal energy (heat) per 1 kWh electrical power used (and billed).
Portable Space heater = 3412 BTU of thermal energy (heat) per 1 kWh electrical power used (and billed).
If your "electric furnace" is a heat pump they you likely are getting 2x to 3x (maybe 5x) the thermal energy (in BTUs) for the same 1kWh of electrical power. Yes you can get more than 1 unit of heat for 1 unit of electricity. This is possible without violating any commonly misunderstood laws because a heat pump (or AC unit) doesn't create heat (thermal energy), it moves it.
AC unit only moves heat IN ONE DIRECTION (inside house -> outside house)
Heat pump moves heat IN BOTH DIRECTIONS (depending on if you want your house warmer or cooler than ambient temp).
Still even if you have a heat pump a mining rig is superior to provide some or all of your heating needs. Mining rig provides both heat AND cashflow. Unless your mining rig provides 100% of your heating needs you might want to look into replacing your resistance heating w/ a heat pump. It can cut your heating costs in half (or more).