Page 274

NORA Oilheat Technicians Manual

Chapter 13 Heating Systems 13-4 Heating Systems 4. The blower continues to run until the heat in the furnace has been dissipated and the fan control shuts it off. (Usually 100 degrees.) The blower may come back on after a minute or two because some residual heat from the combustion chamber and heat exchanger has risen from the furnace to activate the fan control once more. There are different types of warm air furnaces for different applications. The basic operation of these is similar but the configurations vary. Highboy furnace: The most common furnace is the highboy. It gets its name because the heat exchanger sits on top of the blower within the furnace cabinet. Return air is pulled in through the bottom of the unit and circulated upward across the heat exchanger and then out through the top of the unit. See Figure 13-2. Lowboy furnace: Where height constraints are a consideration, a lowboy furnace is often used. The blower is in a compartment next to the heat exchanger, thereby shortening the overall height of the unit. See Figure 13-3. Counterflow furnace: These units are commonly found in slab type construction and mobile homes and look much like a highboy in outward appearance, but differ in that the blower is located above the heat exchanger. Return air comes in through the top and is distributed out through the bottom of the unit. In this type of furnace an additional fan control is installed below the heat exchanger. The upper control turns the blower on when it Figure 13-2: Highboy furnace Figure 13-3: Lowboy furnace Warm Air Outlet Flue Connection Burner and Controls Filter Return Air Inlet Alternate Location of Filter and Return Air Inlet Burner and Controls Filter Blower Return Air Inlet Warm Air Outlet Flue Connection


NORA Oilheat Technicians Manual
To see the actual publication please follow the link above