Oil Burner Draft: What It Is and How to Measure It

Oil burner draft is the vacuum or suction that exists inside most oil heating systems. It is essential for the proper burning of oil and the efficient operation of the heating appliance. In this article, we will explain the basic concepts of oil burner draft, how to measure it, and how to adjust it if needed.

What is Oil Burner Draft?

Oil burner draft is the difference in pressure between the flue gases and the outside air. It is caused by three factors:

  • Chimney height: the higher the chimney, the greater the draft.
  • Flue gas temperature: the hotter the gases, the greater the draft.
  • Outside air temperature: the colder the outside air, the greater the draft.

Oil burner draft can be classified into two types:

  • Natural draft: the draft that is created by the thermal expansion of the flue gases. It depends on the chimney height and the flue gas temperature.
  • Currential draft: the draft that is created by the wind or air currents across the top of the chimney. It depends on the outside air temperature and the wind speed.

Oil burner draft can also be enhanced by using an induced draft blower, which is a fan that creates a suction in the flue.

Why is Oil Burner Draft Important?

Oil burner draft is important for the following reasons:

  • It ensures that the combustion air delivery of the burner is adequate and consistent, which prevents smoke and carbon monoxide formation.
  • It regulates the air leakage into the heating system, which affects the carbon dioxide level and the stack temperature, which in turn affect the operating efficiency.
  • It reduces the standby heat losses up the chimney, which saves energy and money.

How to Measure Oil Burner Draft?

Oil burner draft can be measured using a draft gauge, which is a device that measures the pressure difference in inches of water column (WC). The draft gauge can be connected to two locations:

  • Over the fire: the draft gauge is connected to the combustion chamber, where the draft should be between -0.02 and -0.03 WC for units having inputs up to 2.0 gallons per hour (gph). For higher inputs, the draft should be between -0.03 and -0.04 WC.
  • In the stack: the draft gauge is connected to the flue vent connector, which is the pipe that connects the heating appliance to the chimney. The draft should be between -0.04 and -0.06 WC for gas fired power burners and between -0.06 and -0.08 WC for oil fired burners.

The draft measurements should be taken when the heating appliance is operating at steady state, which means that the burner has been running for at least 15 minutes and the flue gas temperature has stabilized.

How to Adjust Oil Burner Draft?

Oil burner draft can be adjusted by using a draft regulator, which is a hinged, weighted door that opens or closes to let extra air into the flue. The draft regulator is installed on the flue vent connector, before the barometric damper, which is a device that prevents backdrafts and downdrafts in the chimney.

The draft regulator can be set by using the following steps:

  • Loosen the lock nut on the draft regulator and move the weight along the arm until the desired draft is achieved in the stack.
  • Tighten the lock nut and check the draft over the fire. If the draft over the fire is too low, move the weight closer to the hinge. If the draft over the fire is too high, move the weight away from the hinge.
  • Repeat the steps until both the draft over the fire and the draft in the stack are within the recommended ranges.

The draft regulator should be checked and adjusted at least once a year, preferably before the heating season, to ensure optimal performance and safety.

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