Boilers circulate water or steam, furnaces circulate hot air, and heat pumps circulate refrigerant to provide heating.
Boilers use natural gas, propane, electricity, or heating oil to heat and circulate water or steam through pipes to radiators in each room.
Furnaces move centrally heated air through ducts to each room. Furnaces use gas, propane, electricity, or oil.
Heat pumps use electricity and refrigerant to transfer outside heat from the air, ground, or water into the home.