Heat is distributed through your home in a variety of ways.  Aside from forced-air systems, which use ducts, there are two heating systems that apply broadly: steam radiators and hot water radiators.  There are also unique heat distribution systems employed for radiant heating, as discussed below.

Steam Radiators

The first central heating systems for buildings used steam distribution because steam moves itself through piping without the use of pumps. Non-insulated steam pipes often deliver unwanted heat in unfinished areas. Therefore, pipe insulation in these areas is usually very cost effective. Care should be used to install fiberglass pipe insulation that can withstand the high temperatures of these delivery pipes.

Regular maintenance for steam radiators depends on whether the radiator is a one-pipe system (where the pipe that supplies steam also returns condensate) or a two-pipe system (where a separate pipe returns condensate). One-pipe systems use automatic air vents on each radiator, which bleed air as steam fills the system and then shut automatically when steam reaches the vent. A clogged air vent will keep a steam radiator from heating up. Air vents can sometimes be cleaned by boiling them in a water and vinegar solution, but usually need to be replaced.

Steam radiators can also warp the floor they are sitting on and their thermal expansion and contraction over time can dig ruts into the floor. Both of these effects can cause the radiator to tilt, preventing water from properly draining from the radiator when it cools. This will cause banging noises when the radiator is heating up.  To solve this problem, shims should be inserted under radiators to pitch them slightly toward the pipe in a one-pipe system or toward the steam trap in a two-pipe system.

In two-pipe systems, older steam traps often stick in either the open or closed position, throwing off the balance in the system. If you seem to have problems with some radiators providing too much heat and others providing too little, this might be the cause. The best approach is often to simply replace all the steam traps in the system.

Steam radiators located on exterior walls can cause heat loss by radiating heat through the wall to the outdoors. To prevent such heat loss, you can install heat reflectors behind these radiators. You can make your own reflector from foil-covered cardboard, available from many building supply stores, or by mounting foil onto a foam board or other similar insulating surface. The foil should face away from the wall, and the reflector should be the same size or slightly larger than the radiator. Periodically clean the reflectors to maintain maximum heat reflection.

Hot Water Radiators

One way to save energy in hot-water systems is to retrofit them to provide separate zone control for different areas of large homes. Zone control is most effective when large areas of the home are not used often or are used on a different schedule than other parts of the home. A heating professional can install automatic valves on the hot-water radiators, controlled by thermostats in each zone of the house. Using programmable thermostats will allow you to automatically heat and cool off portions of your home to match your usage patterns.

Zone control works best in homes designed to operate in different heating zones, with each zone insulated from the others. In homes not designed for zone control, leaving one section at a lower temperature could cause comfort problems in adjacent rooms because they will lose heat to the cooler parts of the home. Zone control will also work best when the cooler sections of the home can be isolated from the others by closing doors. In some cases, new doors may be needed to isolate one area from another. Cooler parts of the home should be kept around 50F to prevent water pipes from freezing; never shut off heat entirely in an unused part of your home.

Radiant Heating

Radiant heating systems involve supplying heat directly to the floor or to panels in the wall or ceiling of a house. The systems depend largely on radiant heat transfer: the delivery of heat directly from the hot surface to the people and objects in the room via the radiation of heat, which is also called infrared radiation. Radiant heating is the effect you feel when you can feel the warmth of a hot stovetop element from across the room. When radiant heating is located in the floor, it is often called radiant floor heating or simply floor heating.

Radiant heating has a number of advantages: it is more efficient than baseboard heating and usually more efficient than forced-air heating because no energy is lost through ducts. The lack of moving air can also be advantageous to people with severe allergies. Hydronic (liquid-based) systems use little electricity, a benefit for homes off the power grid or in areas with high electricity prices. The hydronic systems can also be heated with a wide variety of energy sources, including standard gas—or oil—fired boilers, wood-fired boilers, solar water heaters, or some combination of these heat sources.

Despite their name, radiant floor heating systems also depend heavily on convection, the natural circulation of heat within a room, caused by heat rising from the floor. Radiant floor heating systems are significantly different than the radiant panels used in walls and ceilings.