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NORA Oilheat Technicians Manual

Figure 6-8: Typical installation of an outside air kit combustion requires a great deal of air to operate properly. It competes with the fireplace, exhaust fans and the clothes dryer for air. All of these appliances drawing on the air in a tight house make it difficult for the oilburner to draw in enough combustion air. With the building so tight, the indoor air pressure drops below the outdoor air pressure and the appliance becomes backvented. Odors, soot, smoke and carbon monoxide may be drawn into the building. ‘Isolated combustion’ (ducting outside air directly to the burner) is the best solution to this problem and there are many effective isolated combustion air options available. (See Figure 6-8) Water heater and furnace stack connections When an oil-fired water heater is installed, it is usually necessary to connect the flue to the same chimney as the furnace 6-12 Draft and Venting or boiler. This can be done in two ways: 1. The two flue pipes can be joined together with a Y connector, as shown in Figure 6-9. (‘T’ connectors should NOT be used as they often cause venting problems for both appliances.) The exit, or chimney side of the Y should be at least one size larger than the largest flue pipe. 2. If you do not use the Y fitting, you can make a second opening in the chimney. If two or more openings are provided into one chimney flue, they must be at different levels. The flue pipe from the unit with the lower firing rate should enter at the highest level consistent with available headroom and clearances to combustible material (see Figure 6-10). A separate draft regulator should be installed for each appliance. Developments affecting chimneys and exhaust High efficiency equipment has brought about changes that can affect chimney draft. Some of these developments, such as lower flue gas temperatures, reduced firing rates, and cold start boilers, will reduce the draft produced by chimneys, and can cause operational problems. The most serious consequence of lowered flue gas temperatures is condensation. The water vapor in the combustion products can drop below the dew point, and turn into water. Because of the sulfuric oxides present in the gases, this water is acidic. It creates scale in the heat exchanger, corrodes the flue pipe and attacks the cement in the chimney. A net flue gas temperature of at least 350°F is recommended to avoid this problem. Corrosion resistant chimney liners also help. Chimney check The objective of a chimney check is to identify obvious and serious chimney problems. It is not intended to be a detailed Chapter 6 Draft and Venting Intake Air Hood Draft Control Outside Wall Furnace/Boiler VRV-Vacuum Relief Valve Field AirBoot® or BigBootTM


NORA Oilheat Technicians Manual
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