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NORA Oilheat Technicians Manual

Temperature settings The water and air temperature controls also affect heat loss. The blower on a furnace operates until the low temperature limit is reached, but heat remains in the furnace and can be lost during the off period. The low limit set point often is adjustable and lower settings can sometimes prevent unnecessary heat loss. Aquastat settings for boilers have the same effect. Maintaining excessive boiler temperatures increases off-cycle losses. Excessive firing rates Fuel nozzles that are too large for the heating requirement of the house increase off-cycle loss. Recall that heat loss varies with the off-period time and that large firing rates produce long burner-off times. The solution to this problem is to reduce the nozzle size, provided that the burner will perform well with the smaller firing rate. With fixed head burners, it may be necessary to change the combustion head if you are drastically reducing nozzle size. Selecting the correct nozzle size is an important part of proper service procedures. Reducing firing rates on older units works because most of them are oversized. The three exceptions to this are: steam boilers, boilers with tankless coils, and any appliance where the steady state stack temperature is less than 400°F. In these three cases, the units should be fired to their maximum rating. New units that are properly sized for the load should be fired to the manufacturers’ recommendations. Older units have high stand-by losses Older appliances have larger losses than modern units. Replacement of these outdated units is often the best option for homeowners. Several design features of old units promote heat loss, including: • Open burner head designs (non-flameretention) that allow air to flow during off-cycle • Larger more massive heating units that store (and lose) more heat during the off-period. • Dense combustion chamber materials that can increase stored heat and off-cycle loss • Heat exchange passages that are less restrictive than modern units, allowing larger off-cycle airflows. • Steam boilers that operate at higher Chapter 16 Energy Conservation Figure 16-4: Heat loss through the boiler or furnace jacket Heat Loss Heat Loss Heat Loss Heat Loss Heat Loss Dry Base Boiler Illustrated 16-8 Energy Conservation


NORA Oilheat Technicians Manual
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