The purpose of designing and installing a heating system in a building is to provide proper heat distribution to the various rooms or zones within the building. This can be done by means of various types of heating systems.

A warm-air furnace can be any type of heating device that circulates warmed air to locations where it is needed. One type, the wall heater, draws in cold air near the floor, passes the air over a heating unit, and then exhausts the warmed air to heat the surrounding area Another type is the gravity warm-air furnace. It is a direct-fired furnace that transfers heat by convection In other words, warmed air circulating through the furnace rises through ductwork to the areas to be heated and then, as the air cools, it descends to the furmace to be reheated Since the installation of this type of system requires abasement and large, unsightly ductwork, it is seldom used in new construction.

A more commonly used type of warm-air furnace is the forced-air furnace (fig. 4-5). In this type, an oil or gas burner heats the fins of a heat exchanger. The heat exchanger warms the cool air passing over it. The warmed air is then forced, by fan, through relatively small supply ducts to the areas to be heated. The air is then returned through return ducts to the furnace for reheating. Outside air can be supplied to the return ducts for a continual supply of fresh air.

Forced-air furnaces are controlled by two thermo-stats: a room thermostat to control the burner and another thermostat to control the blower. Most of these furnaces have filters that eliminate any solid particles in the air before it is heated. These furnaces are also frequently equipped with humidifiers to replace moisture that has been removed from the heated air. Ducts for forced-air furnace systems can be round, square, or rectangular in shape and can be fabricated from tin-plated steel, fiberglass, or more commonly, galvanized sheet metal using methods discussed in chapter 11 of Steelworker 3 & 2, NAVEDTRA 10653-G. Insulation for the ducts usually consist of 1/2-inch to 2-inch-thick fiberglass or rock-wool blankets wrapped around the ducts.

Supply and return outlets may be located in walls, ceilings, or floors. The cover for the outlet may be a decorative grill that covers the end of the duct opening, or it can be a register that can be adjusted to vary the amount of airflow. Diffusers are used to direct the flow of air. They can be either adjustable or nonadjustable and can also include a register. Supply outlets carrying only hot air are best located in or near the floor. That way, the hot air is introduced to the coolest part of the room, and the cold air is returned through return outlets located near or in the ceiling. When the ducts are used also for supplying cooled air, then the opposite location arrangement is best. A small building, such as a residence, may have a single return air grill located in a central hallway. In this case, doors leading to the hall are undercut by about 1 or 2 inches.

For a more thorough discussion of warm-airheating systems and equipment, you should read chapter 9 of Utilitiesman 2, NAVEDTRA 10662.

Steam-heating systems consist of a boiler, a piping system, and radiators or connectors. The boiler is fired by oil, gas, coal, or electricity. Although there are many variations and combinations of steam-heating systems, they are all basically either one-pipe or two-pipe systems.

The one-pipe system uses the same pipe to convey the steam to the radiator and to return the condensate to the boils. When the unit is started, the steam pushes air out of the system through thermostatically controlled air wolves at the radiators. When the air has been expelled and steam reaches the valve, the valve closes automatically. As the steam gives up heat through the radiators, it condenses and runs back to the boiler through the bottom of the supply piping. In the one-pipe system, the mains must be large and sloped to allow the condensate to flow back to the boiler without interfering with the flow of steam.

In a two-pipe system, the steam flows into one end of the radiator and out the opposite end through a thermostatically controlled drip trap that is set to open automatically when the temperature drops below 180F. When enough condensate has collected in the radiator to cool it, the drip trap opens, allowing the condensate to flow into return lines where it is carried to a collecting tank.

A radiator used in a steam- (or hot water) heating system usually consists of a series of interconnected, vertical cast-iron sections. As the steam flows through the radiator, the surface of the sections radiates heat to the surrounding walls, objects, and the surrounding air. As the surrounding air is heated, it rises towards the ceiling, setting into motion a convection current that transfers heat throughout the room.

Convectors usually consist of iron or copper pipes surrounded by metal fins and are most often placed near the floor. Openings at the top and bottom of the convector unit allow circulation of air over the fins. That movement of air over the fins transfers heat to the surrounding area. Small connectors placed around the base of the wall are termed baseboard heaters. For a more thorough discussion of steam-heating systems and equipment, you should read chapter 7 of Utilitiesman 2, NAVEDTRA 10662

A water-heating system includes a boiler, a piping system, radiators or connectors (discussed above), and a water-circulating pump that is used to force the water to the radiators or connectors and back to the boiler. For water heating, three types of piping systems are used. The one-pipe system (fig. 4-6) consists of a single supply main that carries hot water to each radiator in turn. To overcome a loss of water temperature at each successive radiator, you must balance the size of the piping or the orifice at the radiator.

Figure 4-7.Two-pipe water-heating system: A. direct return; B. reverse return.

A two-pipe system is shown in figure 4-7. In this system, the supply main carries hot water, and the cooled water is returned through a separate return pipe. For a more thorough discussion of hot-water heating systems and equipment, you should read chapter 10 of Utilitiesman 2, NAVEDTRA 10662.

Unit heaters are either gas-fired units or they consist of coils of tubing that circulate hot water or steam. A built-in fan behind the unit or coils blows the heated air throughout the area it is heating. When used, unit heaters are usually suspended from ceilings or are mounted high on walls in large, open areas of garages, shops, and similar facilities.