The first thing you want to know is what kind of heating or
cooling system is in place. The ones you are most likely to encounter are the following:
Hydronic heating systems. These transmit heat through hot water or steam. They require a boiler, which can be powered by electricity, natural or propane gas, or oil. The boiler heats the water, which is circulated by a pump via pipes to the radiators or baseboards, through which the heat is distributed to the room. Forced hot water is preferable to steam. Steam systems are not as comfortable to live with. Their heat cannot be zoned, and yet it tends to be uneven throughout a house. They dry the air. They are slow to respond. They are noisy. They are inherently less efficient than systems based on hot-water circulation. You won’t find steam heat in many newer homes, but it’s still in place in many older dwellings.
Warm-air systems. These can use electricity, gas, or oil as their primary fuel source. The most common type is forced air, which requires either fans or blowers to circulate the warmed air from the furnace throughout the house. Gravity systems, which rely on the tendency of warm air to rise, are also stifi in use, primarily in older homes. They are far less popular than forced-hot-air systems, however, because they require huge furnaces (which must be located in the middle of the basement) and extensive duct-work and are notoriously inefficient to operate. Another disadvantage of gravity systems is that you cannot operate central air-conditioning through them. Because of all these drawbacks the experts I talk to say that if you have a gravity-hot-air system, you should plan to replace it as soon as possible.
In a natural-gas heating system, a heat exchanger transmits heat from the combustion area (the furnace) to the distribution system. A standard warm-air furnace powered by natural gas has an efficiency rating of about 65 to 70 percent. Newer gas furnaces have an efficiency rating of around 78 percent.
(The standard for measuring energy efficiency is called the Annual Fuel Utility Efficiency Rating. It indicates how much heat you receive for every dollar you spend. The other energy measure you should look for on newer equipment is the bright yellow “Energy Guide” that is now required by law, where manufacturers indicate the estimated annual cost of operating the unit.)
Furnaces powered by oil are similar to gas furnaces, except that the fuel is delivered by truck, as opposed to being piped automatically into your house from an outside gas line. Oil also doesn’t burn as cleanly as gas, and as a result, oil furnaces have to be cleaned regularly to operate at peak efficiency.
Unlike gas and oil systems, electric systems involve no combustion and therefore produce no exhaust. But in most areas, electricity is the most costly energy alternative.
You may encounter an electrically powered heat pump, which can provide both heat and air-conditioning. In cold weather, the pump heats the outdoor air and pumps it through the house. In hot weather, it cools the indoor air and moves it outside. The disadvantage of heat pumps — and the reason you will find them primarily in warmer climates — is that at colder temperatures, below 25 to 30 degrees Fahrenheit, the system can’t draw enough heat from the outdoor air to provide sufficient heat indoors. Consequently a backup heating system is usually needed.