A furnace that's running non-stop is not necessarily bad. During the coldest days in winter, it is normal for a furnace to run almost constantly to keep the home warm. As long as the furnace is running efficiently and not making strange noises, the constant operation is likely nothing to worry about.
Unless you also have a heat pump (which can cause your unit to run frequently to maintain a set temperature during extremely cold weather), your furnace should cycle on and off at regular intervals.
Many people are under the assumption that running their furnace fan all the time will cause it to fail prematurely. Actually, the opposite is true. These fan systems were designed to run all the time and, assuming your system is properly installed with the correct size ductwork, it may even extend the life of the fan.
Although it is perfectly safe to run HVAC continuously, there are a few times you should shut it down. First, if your home is experiencing high summer temperatures and you have ductwork in the attic. It is difficult for even the best-insulated systems to fight off extreme temperatures.
Furnace manufacturers often spread out their recommendations for heating times over 12 hours to avoid overnight heating. The furnaces are designed so that they can heat all day long, so by spreading it out over 12 hours, there are fewer hours where the furnace is using more energy than necessary.
According to Wired, leaving your heat running constantly at a low temperature is best. However, they warn that keeping specific rooms in your home very cold can “reduce the overall efficiency of your heating since those rooms will soak up warmth and make your boiler or heat pump work harder.”
It isn't bad to run your heating system on a 24/7 basis if outdoor weather conditions demand indoor warmth. For many households, maintaining a constant indoor temperature is the only way to survive the winter. Just be aware that this is likely to cause additional wear and tear on your heating system.
While it's possible to run your furnace fan continuously, it still has some slight drawbacks such as: Running older units can cause your electric bills to rise. Ducts and walls can fill with hot air, causing you to use your AC more frequently. Your furnace filter may clog more quickly.
It could cost you hundreds of dollars a year. The average unit has a 500 watt fan, which uses almost as much energy over the course of the year as a refrigerator, resulting in a $50/month bill.
Some homeowners naturally worry about the risks of a breakdown if they run the fan all the time, but this will not be a concern for you if your HVAC system was properly installed and maintained.
"Most electrical fans are designed to be able to run continuously for several hours at a time, for example overnight or during the day, but you'll also need to keep in mind doing that continuously for long periods can cause wear and tear on the motor and other components, shortening its lifespan," continues David.
The blower motor is particularly sensitive to dust and dirt; when it gets too dirty, it can't ventilate itself and may overheat.
Therefore, the fan uses about 360 kWh per month in the ON mode. The average kWh in the US costs about $0.12 so it costs about $43 per month, or about $520 per year, to run a fan continuously. At this point, it should be pretty obvious that AUTO costs less than ON but let's math it out to its logical conclusion.
"Your system's [furnaces] aren't designed to run in temperatures that are below-zero for long periods of times," Marchand said. To help alleviate some of the stress off of systems during these cold temperatures, set your thermostat a few degrees lower than what you're used to.
If the air filter is good to go, lower the temperature on the thermostat. If the furnace continues to run, shut the heating system down completely. If your thermostat is set to a high temperature or if it's very cold outside, the furnace might be running just to keep up with the thermostat's demand for heat.
If the furnace runs too long, it will overheat and shut off before your home reaches your desired temperature. Repairing your home's ductwork will improve heat distribution and your furnace's heating ability while preventing short cycling.
There are a few reasons you should not keep your HVAC fan running continuously. For example, if your ductwork is in the attic, the summer heat can make running the fan impractical. Temperatures well above 100°F can end up blowing down into your main living space. It also won't help if your ductwork is leaking.
Using the “Auto” Setting
Increased energy efficiency by running the fan only when needed. Extended filter life as the fan operates less frequently. Lower energy bills due to reduced electricity usage.
Advantages of the 'On' Setting
So long as you're switching out your air filters regularly, running the furnace on 'On' can help improve the quality of the air inside your home.
Year-Round: If you have a newer HVAC system, leaving the furnace fan on all the time can enhance air quality, regulate humidity, and improve overall energy efficiency.
Incorrect settings on your thermostat or fan limit switch can cause the fan to run continuously. Faulty wiring or a broken fan limit switch can also cause your fan to keep running. You can diagnose and fix some furnace fan issues on your own. Faulty wiring or a broken switch will require professional repair.
Setting your thermostat to auto will allow your system to be more energy-efficient since the fan only runs when the system cycles on, not continuously. Typically, the fan will turn on 30 to 60 seconds after a heating or cooling cycle starts and then turn off a minute after the cycle ends.
During the coldest days in winter, it is normal for a furnace to run almost constantly to keep the home warm. As long as the furnace is running efficiently and not making strange noises, the constant operation is likely nothing to worry about. But in general, your furnace should not constantly be running.
If you are using your home's furnace, no matter the type, keeping it running throughout the day and night is fully safe to keep your home at a comfortable temperature.
Overworking your furnace means you're asking more from your heating system than it's built to provide. When your furnace overworks, it can cause increased wear and tear on the furnace, reduced winter furnace efficiency, and potential breakdowns.