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NORA Oilheat Technicians Manual

outside vent hood (Figure 6-17). Although these models have operated successfully for years, they often cause noise and vibrations in the building. They should be fastened securely to the outside wall or hung from the floor joists to reduce the transmission of noise. Some power-vented systems use a double wall exhaust connection that draws cooler outside air into the outer pipe, and the hot exhaust gases are contained in the inner pipe (concentric venting). This provides a layer of safety between the hot exhaust gases and the combustible wall and floor joist materials and pre-heats the combustion air. System operation: Power-venting requires that the oilburner primary control has delayed valve-on and burner motor-off delay features, similar to pre-purge and post-purge. When the thermostat or aquastat calls for heat, the power-venter motor starts. After the power-venter motor has come up to speed, the pressure switch closes (in one to two seconds). This closes the circuit to the burner primary, allowing Chapter 6 Draft and Venting 6-18 Draft and Venting the burner to operate. After the heating requirement is satisfied, the thermostat or aquastat circuit opens, activating the burner motor off delay (post-purge) cycle. During this cycle, the oil valve closes shutting off the flame, but the power-venter and the burner motor continue to run for a period of time, venting the last of the combustion products and cooling the burner components. Inspection and maintenance: The power-venter should be inspected once a year. • Check to be sure the motor and fan rotate freely. • To prolong the life of the motor, lubricate it as directed by the manufacturer. • Inspect the power-venter wheel to clear out any soot, ash, or coating that inhibits either rotation or air flow. • Remove and clean the air sensing tube. • Remove all foreign materials before operating. Inspect all vent connections for looseness, for evidence of corrosion, and for flue gas leakage. • Replace, seal, or tighten all of the pipe connections as necessary. • Check the choke plate to insure it is secured in place. • Check the barometric draft control to insure the gate swings freely. • Check the safety system devices—start the heating system, and then disconnect the pressure sensing tube from the pressure switch. This should stop the burner. Reconnecting the tube should restart the burner. For proper system installation, set-up and testing, you must follow the manufacturer’s instructions exactly. It is Figure 6-17: Outside vent hood


NORA Oilheat Technicians Manual
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