How to Set the Weight for an HVAC Furnace

An oil-fired HVAC furnace uses a barometric damper with adjustable weight to automatically regulate the amount of air entering the chimney while the oil burner is operating. This damper is a round or oval swinging door that normally is located in the flue pipe that connects the furnace to the chimney. An incorrectly set damper weight can lead to chimney overheating, erratic burning, soot formation, combustion puffbacks and excessive carbon monoxide formation.

Burner manufacturer’s specifications
Screwdriver
Draft gauge

Instructions

- 1
  Inspect the barometric damper for correct operation. The damper should be level and plumb. The door should move freely and should be completely closed if the furnace is not operating. Start the furnace and fire it at its full rate.
- 2
  Insert the sensor tube of the draft gauge through a small opening in the firebox front or door while the furnace is running and take a reading over the fire. Compare the reading to the burner manufacturer’s specifications for correct draft. If the barometric damper is adjusted correctly, the draft gauge reading over the fire for a typical home oil burner generally should be between 0.02 inches of water and 0.03 inches of water.
- 3
  Check the damper adjustment weight on the damper door. Some damper weights screw in or out. Some weights loosen with a screwdriver and slide in or out. If the draft reading is too low, move the weight outward, toward you, to increase the draft. If the reading is too high, move the weight inward, away from you, to reduce the draft.

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