Things You'll Need

Instructions

1

Locate the furnace pressure switch. Write down the ideal "IN of W.C.," or inches of water column, for your particular furnace, which will be located on the furnace pressure switch.
2

Remove the white tube from the furnace pressure switch, and quickly apply a gas “Y” splitter where the white tube was removed. Attach the removed gas tube to one of the slots of the “Y” splitter.
3

Fill a slack tube manometer with water per the product instructions. The amount of water necessary will vary according to the slack tube manometer model. Find this information in the manometer’s owner’s manual.
4

Grab the black tube coming out of the manometer, and attach to the other section of the “Y” splitter.
5

Calibrate the slack tube manometer by twisting the calibration nozzle until the water level is at “0.” The process to calibrate the manometer will vary according to its manufacturer and model number.
6

Activate your furnace by turning up the temperature on your thermostat until you hear the furnace turn on.
7

Return to the manometer and locate the two water columns. The water column on the right should lower while the water column on the left will rise. Measure the difference between the height of the water columns. The difference in water height may need to be calculated differently depending on the manometer specifications. For example, some manometers require users to add the positive and negative difference.
8

Write down the pressure reading from the manometer. Compare this reading to the ideal pressure from the pressure switch.