Heating homes and offices can be broken down into three categories: gravity systems, forced-air systems and radiant systems. Each has its own set of characteristics and operating principles, and understanding them helps to identify ongoing preventative maintenance needs.
With gravity systems, floor furnaces have burners, a fire box and a cast-iron heat exchanger. The heat exchanger heats the air in the immediate area. This type of heating unit is usually located under the floor in a central hallway. Warm air generated from the furnace moves to adjoining rooms through open doors. The floor register is a sturdy grille you can walk on. Gravity heaters are placed in a basement where ducts can carry warm air to floor outlets throughout the building. This heating system needs a basement with at least 7 feet of headroom. Gas fumes exit through a vent running through the roof to the outside. When a fan is placed on this unit, users must put a return air duct from the heated space back to the furnace to force colder air back to the heater to be treated.
In forced-air heating systems, the main part is the central heating furnace, which includes the burner, a fire box, heat exchanger and a fan. Forced-air furnaces also have a filter, a plenum, controls and possibly an electrostatic air cleaner. Supply ducts connected to the plenum carry warm air to the rooms to be heated. Used air returns to the furnace through a register or return-air ducts. There are many types of forced-air heaters, including the forced-air heater up-flow unit and down-flow unit. Horizontal-type forced-air units are installed below the ceiling, in the attic space, or above the roof.
A typical forced-air heater unit has three sections. The first is the blower section. The second section contains the gas or oil burners and the controls. The third section is the firebox and heat exchanger. There’s a vent pipe attached to the third section to send the combustion fumes outside the building. The plenum is at the top of the heat exchanger, and the supply ducts are connected to the plenum.
Radiant central heating systems use hot water, steam or electricity to heat radiators, pipe coils, or resistance cables so they will radiate heat. This is called “thermal radiation.” The major pieces of equipment in a hot water radiant system are the boiler, circulating pump, expansion tank, supply and return piping, and control devices. A hot water system heats water in boilers and pumps it through pipes to radiators, baseboard convectors, or tubing in the floor or ceiling. Radiators and convectors are usually near the outside wall of the rooms. One popular electrical heating option is called the radiant heat ceiling that has resistance cables attached to gypsum lath or wallboard in the ceiling. The cables are spaced about 6 inches apart and covered with gypsum plaster or filler. This type of system provides fast and uniform heat emission and usually costs less than a mechanical system.
With this basic identification in mind, you as a homeowner or building manager can better troubleshoot or maintain the heart of your heat supply this winter.