Keeping your fan on AUTO is the most energy-efficient option. The fan only runs when the system is on and not continuously. There is better dehumidification in your home during the summer months. When your fan is set to AUTO, moisture from cold cooling coils can drip and be drained outside.
"AUTO" is the more energy-efficient option, as it runs the fan only when heating or cooling is actively needed. "ON" keeps the fan running continuously, which can help with air circulation and filtration but may consume more energy.
The only reason to keep it on constantly is if you are trying to keep temperatures in the home as even as possible, it's called stratification. Otherwise it's fine to leave it in automatic so that the fan only runs as required by the furnace to heat, cool, or by the humidifier to humidify.
The fan should run whenever there is a call for heat, or whenever the thermostat fan switch is set to Low, Medium, High, On, or randomly if the thermostat has such a setting, or for a short time after heating if there is logic in the system to do that.
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.
Pros for “Auto”: If you set your furnace fan to “auto,” the fan will only run when the system tells it to in order to keep your home as warm as you want it based on your thermostat settings. This means it's consuming less energy than when it runs non-stop, which means lower furnace bills.
The main benefit of setting the thermostat to 'Auto' is that it will result in more energy efficient usage. This is because the fan will run only when it's required. Also, the air filter will need to be changed or cleaned less frequently when the thermostat setting is set to 'Auto'.
Running your furnace fan continuously in winter has its pros and cons. It can improve air circulation and quality but may also lead to higher energy bills and increased wear on your system.
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.
To put it simply: Yes, the outside fan should run when your heat pump is in heating mode. Here's why. The outside fan is responsible for the transfer of heat from the outdoor air to the refrigerant coils inside the outdoor unit. Even in cold weather there is some heat present in the outdoor air.
When you set it to “on,” the fan runs constantly. When you choose “auto,” the fan only runs when your air conditioner or furnace is running. The “circulate” (or Circ) setting will usually make the fan run about 35% of the time. The fan will operate when the fan is on and about 20 minutes of every hour otherwise.
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.
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.
Leaving your AC fan set to ON allows the moisture in your home to accumulate and reach mold-growing levels of humidity. To ensure that you and your family stay cool and healthy this summer, keep your AC thermostat fan setting to AUTO.
The heater might blow cold air rather than warm if the gas line supply has been turned off. This usually happens when something goes wrong with the heater, and it breaks. For example, maybe there was a problem with a gas valve, the gas supply pipe, or something else in your furnace broke down.
Check the Furnace's Power Switch
If the circuit breaker is functioning correctly, inspect the on/off switch for the furnace. This switch looks like a typical light switch and is usually located directly above the furnace or on a nearby wall.
Since the AUTO setting means the fan is only engaged when the system is on, rather than constantly blowing, AUTO is the most energy-efficient option between the two settings.
Keeping your fan on AUTO is the most energy-efficient option. The fan only runs when the system is on and not continuously.
This approach can reduce wear and tear on the air conditioning equipment because the fan doesn't have to start and stop as often. Running the fan on the AC all the time also helps maintain a more consistent and even temperature throughout your home because air is constantly circulating, eliminating hot and cold spots.
The best benefit of using the automatic fan setting is saving energy. It won't turn on when the AC and furnace aren't doing their thing, so you won't be paying for that energy to keep it running. It also means your fan motor will get to take breaks, reducing wear and tear and the need for repairs or a replacement.
Which Thermostat Setting Is Best: On, Auto, or Circulate? Given the amount of money it costs in increased utility bills and filter purchases to keep your AC fan running constantly, most of the time, you'll want to keep the fan in the “auto” position.
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. During the summer months, the ducts in your attic and close to your walls can fill with warm air, resulting in the fan blowing hot air into your house.
Higher Energy Efficiency — Using the “AUTO” setting helps increase energy efficiency by reducing the amount of energy used to keep your home comfortable. This means you're wasting less electricity and exposing your furnace system to less constant heating.
If someone is at home in the daytime, 72° F (22° C) is a good start, but aim for 68° F (20° C). If everyone is away from home in the daytime or you're asleep at night, we feel 66° F (19° C) to 62° F (17° C) is best.
Lastly, while we do not recommend using “Auto” mode for the heating and cooling function, we do recommend using “Auto Fan” mode to control air circulation as it tends to be the most efficient setting for that function.