The typical residential furnace uses a single-stage blower and burner that runs at a single temperature. These furnaces can turn on and off but cannot vary their output. Instead, they keep your home's temperature around your thermostat's setpoint by turning on, running for a while, and then turning off again. A residential furnace may cycle this way several times per hour.
The length of time your furnace runs will vary based on the outside temperature, your setpoint, and many other factors, but your furnace generally should not run constantly. A furnace that runs continuously without cycling will use excessive energy, wear out more quickly, and likely do a poor job keeping your home comfortable.
Recognizing Excessive Furnace Run Time
If there's no single length of time your furnace should run, how can you recognize when it's running excessively long? First, pay attention to the obvious signs. If your furnace runs for several hours straight, that's almost certainly an indication of trouble. A properly sized furnace shouldn't constantly run on even the coldest days.
However, there's something more important that you should check: your thermostat. In general, your furnace should be able to reach your thermostat's set point relatively quickly. The only exception might be if you're returning to a very cold home after a vacation or otherwise after leaving your furnace off for multiple days.
Still, your furnace should never struggle to maintain your setpoint under normal circumstances. Once the temperature in your home is relatively close to the target, your furnace should only run a few times per hour to maintain that temperature. If you notice your furnace running for long periods to make a few degrees, it's a good sign of trouble.
Understanding Why Your Furnace is Running for Too Long
Once you suspect a problem, your first culprit should be your furnace filter. A dirty filter will restrict airflow, reducing the heat that reaches the rooms in your house. As a result, it might take your furnace much longer to warm your home. If you ignore this problem long enough, the airflow restriction can eventually cause your furnace to overheat and cause other problems.
If replacing your filter doesn't stop your extended run cycles, it may be time to contact a professional. Other potential problems include faulty thermostats, ductwork restrictions, burner issues, or restrictions in your furnace's fresh air supply or exhaust plumbing. Any of these issues can reduce your furnace's ability to provide heat, but diagnosing the problem may require more work.
While extended run cycles may not seem like an issue if your home eventually heats up, they place more stress on your heating equipment, waste energy, and can be early warning signs of a more significant problem. Once you notice your furnace running for too long, it's time to bring in a professional to determine the issue and restore your furnace's performance and efficiency.
Contact a heating services company to learn more.
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