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NORA Oilheat Technicians Manual

Figure 6-4: Outdoor air infiltration caused by the heating system and chimney To Draft Damper Chapter 6—Draft and Venting 6-7 building into the burner air intake and up through the heat exchanger. As it does so, it also takes heat from the heat exchanger as it goes up the chimney. This new hot air keeps the chimney warm, which, in turn, keeps producing draft that cools the building. Old equipment, especially boilers, have very high stand-by losses. New burner air intakes, air handling parts and combustion heads are not as wide open as the old ones, and new heat exchangers are much more restricted than the older types. The result is much higher efficiencies, less off-cycle heat loss and much lower oil consumption. Draft regulators It is necessary to regulate draft because natural draft is so variable. The most common draft regulator is the by-pass or air-bleed type. Since it responds to changes in barometric (atmospheric) pressure, it is also called a barometric draft regulator or damper (Figure 6-5). The regulator consists of a counter weighted swinging door that opens to allow room air to flow into the flue and mix with the exhaust gases. The room air dilutes and cools the exhaust gas which reduces the temperature difference between the gases leaving the chimney and the outside air. This reduces the draft. When the draft drops below the draft regulator setting, the counterweight closes the draft regulator door. It is important to understand that no draft regulator can cause an increase in draft, it can only decrease draft over-the-fire. It also cannot prevent down drafts caused by wind currents blowing down the chimney. Figure 6-5: Draft regulators Chapter 6 Draft and Venting Exhaust Gases Chimney Indoor Air 70°F Cold Outdoor Air Enters House to Replace Exhausted Air Outdoor Air 0 - 60°F House Exhausted Air by Heating Unit and Chimney Fuel Level Fuel Tank To Burner Draft Regulator Boiler


NORA Oilheat Technicians Manual
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