There are two basic configurations used for the distribution
Return air to furnace
Warm air duct
Room Stairs partition
Basement of a forced-warm-air heating system-the extended-plenum and the radial configuration. (See FIG. 14-2.) Regardless of the configuration, there should always be a physical separation from the furnace at the beginning of the duct. The separate sections are usually connected by a heavy canvas fabric. (See FIG. 14-3.) The separation is intended to isolate the distribution system from the furnace so that blower noise will not be transmitted throughout the house.
In the extended-plenum configuration, a large rectangular supply duct extends in a straight line from the plenum mounted on the furnace. From this main duct, branch ducts supply warm air to the various rooms. The large supply duct results in less resistance to airflow and produces a more effective heat distribution for those rooms farthest from the furnace.
Fig. 14-2. Warm-air distribution systems. Top-extended plenum. Bottom-radial.
In the radial configuration, there is no main supply duct. Each branch duct takes off directly from the plenum and runs to the individual room registers. This system is usually found in smaller houses. A variation on the radial configuration is the perimeter-loopduct arrangement, which is intended for houses built on a slab. This configuration uses a duct that encircles the perimeter of the floor slab and is connected to the furnace by feeder ducts. (See FIG. 14-4.)
The branch ducts for both the extended-plenum and the radial configuration will be either rectangular or round. The round ducts are usually relatively small in diameter (4 to 6 inches), have a higher resistance to airflow, and are normally not used for air-conditioning. (Do not confuse these ducts with the insulated flexible ducts used in many central air-conditioning systems.)
The return duct for both configurations is usually made of sheet metal and has a rectangular cross section. However, in some homes with basements, you might find that a portion of the return duct has been formed using a section of the overhead wood framing. This is done by covering the channel that is formed by adjacent joists with sheet metal. (See FIG. 14-5.)
Supply registers and return grille
As discussed earlier, the most effective location for the warm-air supply registers is along the outside walls. If the supply register is not located
Room along the outside wall, and often it is not, the location of the return grille will be important for developing a uniform heat distribution. For optimum distribution, warm air entering the room from the supply register circulates around the room and then leaves through the return grille. If the return grille is located on the same wall as or a wall adjacent to the supply register, there will be a short cycle of the air circulation, which reduces its effectiveness. In this case, warm air discharging from the supply register can be drawn into the return grille before it has a chance to circulate.
You should look for separate return grilles for each room or a centrally located return grille for each floor. When each room has a separate return, the grille should be located on the wall opposite the supply register. If there is a centrally located return, the supply register should be located on the wall farthest from the door. This will provide a better circulation, since the air will flow through the door opening. Also, about 1 inch should be cut off the bottom of the door to allow for air movement while the door is closed.
Balancing the warm-air flow for your personal needs can best be accomplished after you move into the house. The various supply ducts will have dampers that can vary the airflow. By reducing the flow to the registers closest to the furnace, more warm air will flow to the registers farthest from the furnace. In addition, each register will have dampers that can be used for further restricting and “finetuning” the airflow.
Central heating using a heat pump is basically the same as a forced-warm-air system. However, the means by which the furnace is heated differs. The heating element is not a gas or oil burner but a component of a reversed-cycle air-conditioning system. The heat-pump system is discussed in detail in chapter 17.