CINCINNATI - A new tool for gas furnace troubleshooting, named the “Draft Simulator,” has been developed to serve as a reliable way to test pressure switches, ensuring they open and close at their manufactured ratings. The invention is also used in finding a switch with a bad or weak diaphragm and in verifying switch consistency.

The handheld tool was invented by Richard McFarland, an HVAC service technician since 1975. It weighs 13.7 ounces with its battery inside, and measures 6.5 inches long, 3-5/8 inches wide, and 1-3/8 inches thick. Its light weight and handheld size provide for portability and ease of use in the field.

According to McFarland, the Draft Simulator works by connecting to a manometer and the pressure switch using small rubber tubing. After the leads are connected to the pressure switch, a knob at the top can be turned to adjust suction to the pressure switch which, in turn, simulates the behavior of the draft inducer. Without the furnace running, technicians are capable of verifying the operation of any pressure switch.

An unnoticed faulty switch may result in undesired service warranty visits, lost potential income, and additional time spent diagnosing intermittent failures, noted McFarland. “You spend hours and even replace good parts, until finally, you catch it in the act and it was the pressure switch all along,” he said.

Commenting on the Draft Simulator, William Potts, president of Potts Heating & Air Conditioning, said, “It has reduced call backs, and improved our cost of doing business; it even allowed us to earn customers because other companies couldn’t figure out what was going on.”

The Draft Simulator is under U.S. Patent No. 7,441,439 B2. For more information, visit

Publication date:08/09/2010