How To Set Your Thermostat To Automatic?

By in , ,
How To Set Your Thermostat To Automatic?

Merts Heating & Air Conditioning takes a lot of calls from Steger, IL and Crown Point, IN with questions about their thermostats. That’s not surprising because the new digital thermostats can be more than a little confusing, at least until you get used to them.


One common question is whether the HVAC systems should be set to “Auto” or “On” and what is the difference between the two. A good place to start is to understand your furnace and air conditioner sort of have two functions:

  1. First it heats or cools the air inside the house to the correct temperature
  2. Then it uses a blower (fan) to distribute the conditioned air to all rooms

The thermostat controls both functions.


The first thing to be clear about: Choosing Auto or On does not change the temperature in the home. That is strictly controlled by the number you program into the thermostat. But choosing between Auto and On does change the way the air is distributed. When the thermostat is set to Auto the fan only runs during the heating or cooling cycle. Turning the switch to On means the fan or blower will run continuously even when the furnace or A/C is not actively heating or cooling.


With relatively few exceptions, the switch should be set to Auto. The fan only needs to run during active heating and cooling cycles. Running the fan continuously uses more energy and increases wear and tear on the blower and motor. There are some situations in your Illinois or Northwest Indiana home when turning the thermostat to the On position has some advantages:

  • Your air conditioner freezes up—When this happens the ice has to melt before our Merts technicians can perform maintenance on the unit. Running the fan continuously will melt the ice more quickly.
  • Indoor air quality concerns—Examples include extremely dusty conditions, the peak of the allergy season, or odors in the house from cooking, painting, etc. Running the fan all the time will keep the air cleaner by circulating it through the filter continuously.
  • Hot and cold spots—Running the fan all the time may help to make the temperature in the house more consistent. Truthfully however, running the fan should be considered a stop gap measure at the very least. There are many other maintenance and repair strategies to deal with hot and cold spots on a more permanent basis.


I hope this took some of the mystery out of the thermostat settings in your Steger, IL or Crown Point, IN home. Merts Heating & Air Conditioning is always here to help with any HVAC repair, replacement, or maintenance needs. We’ve been delivering “Quality and Honesty Since 1952.” Learn more by liking us on Facebook and following us on Twitter.