Gas furnaces have several safety features, including a pressure switch. Whether you have an older low-efficiency gas furnace or a newer modulating furnace, it will produce flue gases. Also known as stack gases, it’s the byproduct of burning natural gas. To ensure that flue gases are properly ventilated, gas furnaces feature a pressure switch.
What Is a Pressure Switch?
A pressure switch is an electrical switch that’s designed to shut down gas furnaces in the event of a pressure problem.
Like all electrical switches, it supports two states: open and closed. All electrical switches can toggle between an open state and a closed state – and pressure switches are no exception. Electricity can’t travel through an open switch; it can only travel through a closed switch.
Pressure switches receive their namesake from their reliance on pressure. They toggle between an open and closed switch based on the exhaust pressure. If the pressure switch detects negative pressure, it will remain closed. Electricity will travel through the closed pressure switch so that the gas furnace continues to run. If the pressure switch detects positive pressure, it will open, thus shutting down the gas furnace.
Why Do Gas Furnaces Need a Pressure Switch?
Gas furnaces need a pressure switch to prevent flue gases from leaking into homes. Negative pressure is used to vent flue gases to the exterior. Normally, the blower will produce negative pressure that forces the flue gases out of the gas furnace and through a flue pipe. The flue gases will then be expelled outside.
Gas furnaces can experience pressure problems. Rather than negative pressure, they may produce positive pressure. Positive pressure means the flue gases won’t be expelled outside. Rather than rising into the flue pipe, the flue gases will enter your home’s interior.
How to Tell If Your Gas Furnace Has a Bad Pressure Switch
If your gas furnace has a bad pressure switch, it may not turn on. Alternatively, a bad pressure switch may simply allow flue gases to leak into your home. You may not smell the flue gases, but they’ll continue to accumulate as your gas furnace runs. This phenomenon is known as backdrafting.
Backdrafting is a safety hazard. Flue gases can contain toxic compounds like carbon monoxide (CO). A bad pressure switch will allow these flue gases to build up inside of your home. If you believe this safety feature has failed, you should get your gas furnace professionally serviced as soon as possible.
If you are experiencing a problem with your air conditioning or heating call us at 512-336-1431 to schedule an appointment. We’ll be glad to come out and take a look at the issue.
1431-183 A/C & Heating proudly serves Round Rock, Georgetown, Cedar Park, Pflugerville, Leander, Liberty Hill, and North Austin.
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