Because of strict EPA regulations, most HVAC equipment is of a consistently high grade. Many older homes are equipped with boilers, which use water to circulate heat instead of a blower. Boilers are no longer the huge mass of iron you might remember, and new models are as energy efficient as furnaces. Many people prefer the heat produced by boilers, which makes a whole house feel warm by maintaining consistent temperature. Boilers can also control your hot-water heater.
Boilers are either gas or oil fueled.
In the summer, they work like air conditioners, pulling heat from inside the house and forcing it outside. In the winter, it works in reverse, gathering heat from outside and distributing it through the house. Heat pumps have an electrically powered backup for especially cold days. Eco-friendly geothermal heating is a kind of heat pump. Instead of pulling heat from air, pipes are buried underground to pull heat from the earth.