The fan is one of the loudest parts of your furnace, so you can almost always tell when it’s running. That’s why it can be concerning when your thermostat says your home is at the right temperature but the sound of your fan running never seems to disappear. Today we’re going to explain a couple of reasons why this might be happening by answering the question, “Why is my furnace fan always on?”

Why is my furnace fan always on?

  • Thermostat fan setting is set to “on.” Your thermostat has a dedicated setting for your furnace’s fan. This setting can either be set to “on” or “auto.” If this setting is currently set to “on,” then your fan will always run regardless of whether or not your furnace is in a heating cycle. Change this setting to “auto” so that your fan will turn off after every heating cycle.
  • The limit switch is malfunctioning. Your furnace’s limit switch is responsible for telling your air handler when to turn it on and off. If this device begins to malfunction, your fan might never receive the memo that it’s time to turn off and it will continue to run even when a heating cycle has ended.
  • You have a variable speed furnace. Variable speed furnaces have an air handler that operates at many different speeds depending on the demand for air at any given time. A variable speed air handler runs almost all the time, albeit typically at a low setting that is much quieter than the higher setting that’s used during heating cycles. If you have a variable speed furnace, it’s completely normal for your fan to run in between heating cycles, as long as it does so at the lower and quieter settings.

Prevent fan problems with annual tune-ups

If you want to keep your furnace’s fan running properly, it’s important to schedule annual tune-ups for your furnace. During your tune-ups, we’ll inspect your system for any problems like a malfunctioning limit switch that might cause your furnace fan to always be on. In addition, we can answer any questions you might have about why your furnace fan runs too frequently.
If you have any questions about why your furnace fan is always on, or if you’d like a heating system serviced or installed in your home, contact Jerry Kelly Heating & Air Conditioning, your St. Charles, MO, furnace installation and repair contractor. We service the St. Louis area, including towns like St. Paul, St. Peters, and Town and Country, MO.

photo credit: stevendepolo via photopin cc

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