Some types of warm air systems have numerous ducts, blowers, and registers, so that the warm air from the furnace will be forced through the entire house. Additional registers and ducts are provided so that the cold air will be brought back to the furnace to be heated.
Other types of warm air systems draw the cold air directly from outdoors by means of a large duct, heat it by circulation through the furnace, and thus provide a continuous supply of warm, fresh air.
The kind of warm air system installed' will depend upon the heating requirements of the house. A pipe-less furnace, for example, sends a blast of hot air through one central register.
The inefficiency of this kind of system in a large house is that the warm air will escape through the first available opening upstairs and leave the rooms on the lower floor unheated. Also, if the rooms have high ceilings, there will be a concentration of heat in the upper portion of the room, while the lower part remains relatively cold.
A pipeless furnace is best suited for small, compact homes where ample opportunity is provided, by means of doors and other openings, for the warm air to circulate about the house.
The effectiveness of a warm air system with ducts to bring the air to various portions of the house will depend on how well the system is installed.
In the first place, the ducts should be as free of sharp angles and turns as is possible. Sharp bends in the ducts will increase the resistance to the flow of warm air from the furnace. If a warm air system is not giving satisfactory service, check to see if there are any sharp bends that can be eliminated. Another cause of resistance to the passage of air is that the ducts slant downward from the furnace rather than up to the registers.
Preheating cold air
A warm air system can be made considerably more efficient if you connect a duct from air intake at bottom of the furnace to a register on first floor. Thus air need be heated less and fuel is saved. Ducts should not be run inside an exterior wall or heat will be lost. Registers should be low on a wall as warm air rises.
Eliminating dust and dirt
Newer warm air heating systems usually have a filter to remove dust and dirt from the warm air. Since older systems lack such filters, remove the registers and place a piece of cheesecloth in back of them. The register, when replaced, holds the cheesecloth in place, but it must be removed now and then to be washed or replaced by new cheesecloth.
One new filter works on an electrical basis. As air and dust pass through filter, the dust gets an electrical charge. Then a metal plate containing an opposite electrical charge attracts it.
The air in a house will often become very dry when the house is heated with a warm air system. This dry air is not only uncomfortable but unhealthy as well. Warm air furnaces are equipped with water pans that help maintain a comfortable humidity, providing they are kept full of water. If, in spite of a full water pan, the air in the house is still too dry, a humidifier can be purchased to remedy the situation.
Before you increase the moisture content of the air too much, remember that this increase will cause condensation on the walls and windows of the house during the heating season.