Cut down on energy costs and prevent damage to your furnace by addressing a gas furnace that's overactive or short cycling. Besides the need for consistently comfortable temperatures, this issue could cause long-term safety issues to your home, making it very important to address. From a faulty thermostat to a dirty filter, there are several possible causes to investigate.
The HVAC industry is a worldwide enterprise, with roles including operation and maintenance, system design and construction, equipment manufacturing and sales, and in education and research. The HVAC industry was historically regulated by the manufacturers of HVAC equipment, but regulating and standards organizations such as HARDI, ASHRAE, SMACNA, ACCA, Uniform Mechanical Code, International Mechanical Code, and AMCA have been established to support the industry and encourage high standards and achievement.
Ductwork pinging or popping. If you hear a pinging or popping sound coming from metal ductwork, this may be caused by thermal expansion or by air blowing past a loose flap of metal. Track along the duct runs, listening for the sound. If you find it, make a small dent in the sheet metal to provide a more rigid surface that’s less likely to move as it heats and cools.

The standards do not require you to change your existing central air conditioning units, and replacement parts and services should still be available for your home’s systems. The “lifespan” of a central air conditioner is about 15 to 20 years. Manufacturers typically continue to support existing equipment by making replacement parts available and honoring maintenance contracts after the new standard goes into effect.
Air conditioners can create a lot of water because they remove moisture from the air. To get rid of this, they have a [usually plastic] drain pipe that comes out of the side of the air handler. Over time, algae can block this pipe and, when it does, the AC won’t work. In fact, some condensate drains have a float switch that won’t let the AC run if water backs-up. Water can also puddle around the unit or flood the area. To deal with condensate problems, please see Air Conditioner Leaks Water, below.
The fan limit switch controls the furnace blower. The fan limit switch has three settings: “Fan On”, “Fan Off”, and “Limit”. In the “Fan Off” setting, the blower will only operate if there is warm air in the plenum to prevent cool air from blowing into the home. The “Fan On” setting will keep the blower operating even after the burner has shutdown, making sure that all of the hot air produced is circulated. The “Limit” setting is a safety control that will turn the burner off in the rare event that the air in the warm air plenum reaches an unsafe temperature. This may be the case if ducts are blocked or if the system controls are malfunctioning.
Finally, don't underestimate the thermostat as a potential reason why your furnace is not working. Everything on the heating unit itself may function perfectly, but your home still will not heat right if the console you use to set the temperature doesn't communicate your input. A faulty thermostat can either be due to the wall unit itself, or the wiring that connects it to your furnace. Average thermostat repair costs are between $108 and $282, including labor. Replacement costs, of course, depend on the thermostat you choose. Visit our thermostat repair cost guide to learn more about this type of issue.

Furnaces and thermostats are not mix-and-match appliances. Using the wrong type of thermostat with a furnace will cause operating problems and can be dangerous. Although thermostats look similar, they are designed very differently. There are numerous types of heating systems and thermostat systems and they need to be coordinated for safe and proper operation. There are three types of thermostat systems used today: millivoltage, low voltage, and line voltage.​

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