HEAT DISTRIBUTION SYSTEMS Heat is distributed through a variety of ways. Steam heating is one of the oldest heating technologies, but the process of boiling and condensing water is less efficient than modern systems and suffers from lag times be- tween the boiler turning on and the heat arriving in the radiators. The first central heating systems used steam distribution because steam moves itself through piping without the use of pumps. Non insulated steam pipes often de- liver unwanted heat. Fiberglass pipe insulation that can withstand the high temperatures of these delivery pipes is very effective. Regular maintenance for steam radiators depends on whether the radiator is a one-pipe system (the pipe that supplies steam also returns condensate) or a two-pipe system (a sep- arate pipe returns condensate). One pipe systems use automatic air vents on each radiator, which bleed air as steam fills the system and then shut auto- matically when steam reaches the vent. A clogged air vent will keep a steam radiator from heating up. Air vents can be cleaned by boiling them in a water and vinegar solution, but usually need to be replaced.
Steam radiators can also warp the floor and their thermal expansion and contraction over time can dig ruts into the floor. These effects can cause the radiator to tilt, preventing water from properly draining from the radiator when it cools and cause banging noises when the radiator is heating up. Shims should be inserted under radiators to pitch them toward the pipe or the steam trap in a two-pipe system. Older steam traps often stick in either the open or closed position, throwing off the balance in the system. The best approach is to replace steam traps in the system. Steam radiators located on ex- terior walls can cause heat loss by radiating heat through the wall to the out- doors. To prevent such heat loss, foil-covered cardboard reflectors should be installed behind these radiators. The foil should face away from the wall, and the reflector should be slightly larger than the radiator. Hot-water radiators are one of the most common heat distribution systems in newer homes. They may be a baseboard-type radiator or of an upright design. The most common problem in hot-water systems is unwanted air in the system. At the start of each heating season it is necessary to go from radiator to radiator and open each bleed valve slightly, then close it when water starts to escape through the valve. To save energy in hot-water systems it is necessary to provide sep- arate zone control for different areas of the building. Automatic valves on the hot water radiators, controlled by programmable thermostats in each zone of the house will allow to heat and cool off portions of the house automatically.

5. Answer the questions.
1. What are the most common heat distribution systems?
2. What are the main disadvantages of steam heating?
3. What does regular maintenance for steam radiators depend on?
4. What can cause heat loss?
5. What is the main problem with hot-water radiators?
6. What are the ways of saving energy in hot-water systems?
7. Which of these systems is more effective from your point of view?