Oil Furnace Draft Gauge: What It Is and How It Works

Oil furnaces are heating systems that use oil as fuel to produce heat. They require a proper draft, or vacuum, in the flue to ensure efficient and safe combustion of the oil. A draft gauge is a device that measures the draft intensity, or pressure difference, between the flue and the surrounding air. A draft gauge can help you monitor and adjust the draft in your oil furnace to optimize its performance and prevent problems such as smoke, soot, and carbon monoxide.

How to Measure Draft in an Oil Furnace

To measure the draft in an oil furnace, you need a draft gauge, a flexible tube, and a drill. A draft gauge is a simple instrument that consists of a U-shaped tube filled with water or oil, a scale, and a pointer. The draft gauge can be either analog or digital, depending on your preference.

The steps to measure the draft in an oil furnace are as follows:

  • Turn off the oil furnace and let it cool down.
  • Locate the flue vent connector, which is the pipe that connects the furnace to the chimney.
  • Drill a small hole in the flue vent connector, about 6 inches above the furnace and before the barometric damper, if any. The hole should be slightly larger than the diameter of the flexible tube.
  • Insert one end of the flexible tube into the hole and secure it with tape or a clamp. Make sure the tube is not kinked or blocked.
  • Connect the other end of the flexible tube to the draft gauge. Make sure the gauge is level and stable.
  • Turn on the oil furnace and let it run for a few minutes until it reaches its normal operating temperature.
  • Read the draft gauge and record the value. The draft gauge will show the draft intensity in inches of water column (WC). A negative value indicates a draft, while a positive value indicates a backdraft.

How to Interpret Draft Measurements

The draft intensity in an oil furnace depends on several factors, such as the chimney height, the flue gas temperature, the outside air temperature, and the wind speed and direction. The draft intensity can vary throughout the day and the season, depending on the changes in these factors.

The ideal draft intensity for an oil furnace is between -0.02 and -0.05 WC, according to the Combustion Technology website. This range ensures that the oil burner receives enough combustion air and that the flue gases are properly vented out of the chimney. A draft intensity within this range also minimizes the heat loss and the fuel consumption of the oil furnace.

If the draft intensity is too low, below -0.02 WC, it means that the flue gases are not moving fast enough through the flue. This can cause incomplete combustion, smoke, soot, and carbon monoxide accumulation in the furnace and the flue. A low draft can also reduce the efficiency and the lifespan of the oil furnace.

If the draft intensity is too high, above -0.05 WC, it means that the flue gases are moving too fast through the flue. This can cause excessive combustion air, high stack temperature, and high oxygen level in the flue gases. A high draft can also increase the noise and the wear and tear of the oil burner.

How to Adjust Draft in an Oil Furnace

To adjust the draft in an oil furnace, you need a barometric damper, which is a hinged, weighted door that regulates the amount of air that enters the flue. A barometric damper can be either manual or automatic, depending on the type and model of your oil furnace.

The steps to adjust the draft in an oil furnace are as follows:

  • Locate the barometric damper, which is usually installed on the flue vent connector, between the furnace and the chimney.
  • Loosen the screws or nuts that hold the weight on the barometric damper. Do not remove the weight completely.
  • Slide the weight along the arm of the barometric damper until you reach the desired draft setting. The draft setting is marked on the scale of the barometric damper. The closer the weight is to the hinge, the lower the draft. The farther the weight is from the hinge, the higher the draft.
  • Tighten the screws or nuts that hold the weight on the barometric damper.
  • Check the draft gauge again and verify that the draft intensity is within the ideal range. If not, repeat the steps until you achieve the optimal draft.

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