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NORA Oilheat Technicians Manual

Figure 6-6: Draft regulator locations: Correct and incorrect The draft regulator should be installed in the flue pipe between the chimney and the stack mounted primary control, if there is one. It should be at least 10 inches to 12 inches from the control and 18 inches is preferred. If installed closer to the control, the cool air from the regulator can cause the unit to shut off on safety even when the system is operating properly. See Figure 6-6 for draft regulator locations. Some newer heating appliances are designed to operate without a draft regulator. The burners create enough static pressure to move the combustion products up the chimney and the heat exchangers are tight enough to resist the effects of strong and variable negative draft. As with all Oilheat appliances, always follow the manufacturers’ instructions regarding draft. Measuring chimney draft We measure draft in ‘inches of water column.’ One inch of water column is the pressure difference required to lift a column of water one inch up a tube. Typically, chimney drafts required for oil-fired heating 6-8 Draft and Venting units are close to -.05 inches. Draft is checked at two places: over-the-fire (draft at the top of the combustion area) and in the flue pipe, as close to the breech as possible. Before any measurements or adjustments are made, the condition of the draft regulator should be checked. The pivot shaft should be horizontal, not cocked, and the door should swing freely. Have burner run long enough to be sure that the chimney is warm. Draft over-the-fire Draft over-the-fire is the most important draft measurement and should always be measured first. The over-the-fire draft must be constant so burner air delivery will also be constant. The setting must be high enough to ensure that combustion products do not leak into the building, but are drawn through the heat exchanger. Normally, an over-the-fire draft of -.01" to -.02" will be sufficient. If the over-the-fire draft is higher than manufacturers recommendations (typically - .02"), the draft regulator weight should be adjusted to allow the door to open more. If the draft is below manufacturer’s recommendations, the weight should be adjusted to close the regulator door. However, some equipment is able to operate under very low or zero draft. In fact, some appliances operate under positive pressure, so that when an over the fire reading is taken, the draft is positive. If the draft regulator door is already wide open, you may need to install a larger or second regulator. Draft at the breech After setting the over-the-fire draft, the draft at the breech should be measured. The draft in the flue pipe will be slightly higher than the over-fire draft due to the restric- Chapter 6 Draft and Venting Correct Location Incorrect Location (Not Less Than 18" Away from Wood Joints or Ceiling Primary Control ¼" Holes for Combustion Tests Boiler or Furnace 10" or More


NORA Oilheat Technicians Manual
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