To read your thermostat correctly, you need to understand the difference between the System settings (Heat, Cool, Off) and the Fan settings (Auto, On). The most common mistake homeowners make is setting the Fan to “ON,” which runs the blower 24/7 even when the furnace isn’t heating, causing cold drafts. For standard operation, keep your System set to “HEAT” or “COOL” and your Fan set to “AUTO” to ensure the blower only runs during a heating or cooling cycle.
Master your thermostat to save money and stay comfortable.
- System Mode: Selects whether you want heating, cooling, or the system off.
- Fan Auto: The fan only runs when the furnace/AC is actively working (Best for efficiency).
- Fan On: The fan runs continuously, circulating air 24/7 (Good for filtration, bad for bills).
- Hold: Overrides your programmed schedule to keep a steady temperature.
Table of Contents
- The Two Main Controls: System and Fan
- Fan Settings: “Auto” vs. “On” (The Big Confusion)
- System Modes: Heat, Cool, and Em Heat
- Program Settings: Run, Hold, and Permanent Hold
- Frequently Asked Questions About Thermostats
- Take Control of Your Home Comfort
The Two Main Controls: System and Fan
Modern thermostats, whether digital or analog, generally have two main switches or menu options that control your entire HVAC system.
- The System Switch: This tells the equipment what to do (Heat up, Cool down, or turn Off).
- The Fan Switch: This tells the blower motor how to move the air (Run constantly or only when needed).
Understanding how these two interact is the key to a comfortable home.
Fan Settings: “Auto” vs. “On” (The Big Confusion)
This is the source of 90% of thermostat-related comfort complaints.
| Setting | What It Does | Pros | Cons |
| Fan AUTO | The blower fan turns on only when the furnace or AC is running. | Most energy-efficient; better humidity control in summer. | Air can become stagnant between cycles. |
| Fan ON | The blower fan runs continuously, 24 hours a day, regardless of temperature. | Better air filtration; more even temperatures in multi-story homes. | Higher electric bills; can blow cool air in winter; increases humidity in summer. |
Our Recommendation: For most homes in Otter Tail County, leave the fan on AUTO. Only switch it to ON if you are cleaning the house and want to filter dust out of the air quickly.
System Modes: Heat, Cool, and Em Heat
- HEAT: Activates your furnace or boiler. The system will run until the room reaches your set temperature.
- COOL: Activates your air conditioner or heat pump.
- OFF: Turns the entire system off. It will not heat or cool, regardless of the temperature in the house.
- EM HEAT (Emergency Heat): You will typically only see this if you have a heat pump.
Definition: Em Heat (Emergency Heat)
This setting bypasses the energy-efficient heat pump entirely and uses the backup heating source (usually electric resistance strips or a gas furnace) as the primary heat. It is expensive to run and should only be used if the heat pump is broken or iced over.
Program Settings: Run, Hold, and Permanent Hold
If you have a programmable thermostat, you will see these options.
- Run Schedule: The thermostat follows the pre-programmed times and temperatures you set (e.g., turning down the heat while you are at work).
- Hold (Temporary Hold): If you manually change the temperature, the thermostat will “hold” that new temperature until the next scheduled time block begins (e.g., until you wake up the next morning), then it goes back to the schedule.
- Permanent Hold: This overrides the schedule completely. The thermostat will act like a manual unit and keep the temperature at that setting forever until you press “Run” again.
Frequently Asked Questions About Thermostats
Why is my thermostat screen blank?
The most common cause is dead batteries. Pull the thermostat housing off the wall plate and check for AA or AAA batteries. If replacing them doesn’t work, check your circuit breaker.
Why is my furnace blowing cold air?
Check your Fan setting. If it is set to “ON,” the fan is circulating room-temperature air even after the furnace has turned off. Switch it to “AUTO.”
What does the “Wait” message mean?
This is a safety delay feature (usually 5 minutes) to protect the compressor in your AC or heat pump from short-cycling if the power blinked or you adjusted the temperature too quickly.
Where is the best place to put a thermostat?
It should be on an interior wall, away from direct sunlight, drafts, windows, and supply vents. Placing it in a hot or cold spot will give false readings and make the rest of the house uncomfortable.
Should I set my thermostat to 90 degrees to heat the house faster?
No. Your furnace heats at the same speed regardless of the setting. Setting it to 90°F just makes the furnace run longer, not hotter, and usually results in the house getting uncomfortably hot.
What is the difference between a smart thermostat and a programmable one?
A programmable thermostat repeats a set daily schedule. A smart thermostat (like Nest or Ecobee) connects to Wi-Fi, allowing you to control it from your phone and learning your habits to save energy automatically.
Take Control of Your Home Comfort
Your thermostat is the brain of your HVAC system. By understanding these simple settings, you can stop wasting money on electricity, prevent cold drafts, and ensure your home is exactly the temperature you want it to be.
By: The Team at Tim’s Heating & Refrigeration
Last Updated: December 27, 2025
Credentials: Otter Tail County’s trusted choice for HVAC service with over a decade of experience in residential and commercial heating systems.