Boilers
Boilers use gas, oil or electricity to heat water or steam which is then circulated through your home into radiators or baseboard heaters. The heated water or steam releases heat into your home and heats it in turn. While not quite as energy efficient as a high efficiency furnace, boiler heat is perfect for homes with existing radiators and no room for vents and ductwork. It also has less of an impact on indoor air quality since there is no air movement and boilers tend to last a very long time when well maintained.
Heat Pumps
Heat pumps are becoming increasingly popular, especially in milder climates where it rarely gets below 40 degrees F. A heat pump uses the same technology as an air conditioner to extract heat from outside using a compressor, evaporator coils, and condenser coils with refrigerant.
It is most efficient in the spring and fall when temperatures are mild, but it uses much less energy than either a boiler or furnace and it can be used in the summer to cool your home. When properly maintained, a heat pump will last 10-20 years and save quite a bit of money, though it is recommended that you have an emergency heat source for days when the temperature outside gets below 40 degrees F.