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NORA Oilheat Technicians Manual

temperatures than hot water systems. The off-cycle heat losses for old units, especially steam boilers may be more than 20%. Jacket heat loss Useful heat is lost through the walls of the boiler or furnace. This is referred to as “jacket” or “casing” loss and it reduces the amount of heat delivered to heated areas of the home, Figure 16-4. The size of this loss depends on the heating unit design and the location of the boiler or furnace within the house. Jacket heat loss is largest when the burner is operating and heat from the flame passes through the combustion chamber and out of the unit through its outer jacket. Heat losses through boiler jackets were measured at Brookhaven National Laboratory and ranged from about 1% to 12% of the fuel’s heating value. Generally, wetbase boilers had the lowest losses and drybase units had the highest. Old boilers, especially coal-conversion units with large firebrick combustion chambers, had the largest jacket heat loss. Pipe and duct heat loss The heat from a boiler or furnace is transported to the home through hot water (or steam) pipes or warm air ducts. Heat loss that occurs between the heating unit and the living space causes system inefficiency (see Figure 16-5). The level of efficiency depends upon how and where the pipes or ducts are installed, the size of the distribution system, the amount of thermal insulation and the location of the pipes and ducts within the building. Hot water piping that is not insulated adequately can increase fuel use. The water in pipes leading to the radiators is generally between 180° and 200° Fahrenheit. These pipes often are located in cool basements and in other unheated spaces. If these pipes are not insulated, heat will be lost from the boiler water before it reaches the radiators in the house. More fuel must be consumed to compensate for these heat losses. Similarly, heat loss from warm air ducting reduces the useful heat output of a furnace. Furnace ducts typically waste more heat than piping losses. There are two reasons for this. First, warm air ducts have a Chapter 16 Energy Conservation Figure 16-5: Heat loss from warm air ducts and hot water pipes Chapter 16—Energy Conservation 16-9 To House From House Warm Air Heat Ducts Loss Heat Loss Warm Air Furnace Heat Loss Hot Water Boiler Hot Water Pipes Heat Loss Radiator


NORA Oilheat Technicians Manual
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