What you can change yourself on most thermostats

You can change the temperature setting, the mode (heat, cool, or fan), and the schedule on most modern thermostats without calling anyone. These are the everyday adjustments a thermostat is designed for you to make. If your thermostat has a screen and buttons or a touchpad, you own the right to adjust it.

The settings you can safely change include raising or lowering the target temperature, switching between heating and cooling modes, adjusting fan speed, and programming when the system turns on and off. You can also change the display from Fahrenheit to Celsius on many models. None of these changes will damage the system or void a warranty—they are normal operation.

What you should not change are the refrigerant charge, the electrical connections, the gas valve settings, or anything inside the unit itself. Those require a licensed HVAC technician. The line between "user adjustment" and "technician work" is straightforward: if you have to open the unit or touch anything that is not a button, dial, or screen, stop and call someone.

Key Takeaways

  • Temperature, mode, fan speed, and schedule are all settings you can change on your thermostat without professional help.
  • Programmable and smart thermostats let you set different temperatures for different times of day, which can lower your heating and cooling costs.
  • If your thermostat is not responding to button presses or screen taps, the problem is usually a dead battery or a tripped breaker, not a broken thermostat.
  • Never open the thermostat case or adjust internal components; those changes require a licensed HVAC technician.
  • Changing the thermostat setting will not affect your warranty as long as you do not physically alter the device.

How to change the temperature on a manual thermostat

A manual thermostat has a dial or a lever you turn or slide to set the temperature. Turn the dial clockwise to raise the temperature or counterclockwise to lower it. The number you align with the pointer is the target temperature your system will try to reach. That is all there is to it.

Some older manual thermostats have separate dials for heating and cooling. If yours does, set the heating dial to the lowest temperature you want in winter and the cooling dial to the highest temperature you want in summer. The system will heat if the house drops below the heating setting and cool if it rises above the cooling setting.

How to change settings on a programmable thermostat

A programmable thermostat has a screen and buttons. To change the temperature right now, look for a button labeled "up" or "down" or a plus and minus symbol. Press it until the display shows the temperature you want. This change takes effect when ready and overrides any schedule you have set.

To change the schedule itself, look for a button labeled "program," "schedule," or "settings." Press it and follow the on-screen prompts. You will usually be asked to choose a day (or weekday/weekend), a time, and a temperature. Enter each piece of information and confirm. Most programmable thermostats let you set four or more temperature changes per day—for example, lower heat when you leave for work and raise it an hour before you come home.

If you make a mistake while programming, look for a "clear" or "reset" button. Pressing it will erase the schedule you just entered so you can start over. Do not press "reset" if you mean to keep your schedule; that button usually erases everything.

How to change settings on a smart thermostat

A smart thermostat like a Nest, Ecobee, or Honeywell Home connects to your home WiFi and can be controlled from your phone. To change the temperature, use the physical dial or screen on the thermostat itself, or open the manufacturer's app on your phone and adjust the temperature there. Both methods work equally well.

To change the schedule, open the app and look for "schedule," "routines," or "automation." You can usually set different temperatures for weekdays and weekends, and some models let you create custom schedules that change based on whether anyone is home. The app will walk you through the steps.

Smart thermostats often have features like geofencing (the system adjusts temperature based on whether your phone is near home) and learning (the system remembers your patterns and adjusts automatically). These are optional. If you do not want them, you can turn them off in the app settings without affecting the basic heating and cooling.

When the thermostat does not respond to changes

If you press buttons or tap the screen and nothing happens, the thermostat battery is usually dead. Most thermostats run on two AA or AAA batteries. Open the battery compartment (usually on the back or side) and replace the batteries with fresh ones. The thermostat should respond within a few seconds.

If the thermostat has a screen but it is blank or very dim, a dead battery is almost certainly the cause. If the screen is on but the buttons do not work, try replacing the batteries anyway—sometimes the power is too low for the buttons to register even though the screen still lights up.

If replacing the batteries does not fix it, check your electrical panel for a tripped breaker. Thermostats that are wired into your home's power (rather than battery-powered) will stop working if the circuit breaker trips. Look for a breaker labeled "thermostat," "HVAC," or "heating and cooling" and flip it back on if it is in the off position.

If the thermostat still does not respond after you have replaced batteries and checked the breaker, call an HVAC technician. The thermostat itself may be faulty, or there may be a wiring problem inside the unit.

What happens when you change the thermostat setting

When you raise the temperature in heating mode, your furnace or heat pump will turn on (if it is not already running) and stay on until the house reaches the temperature you set. When you lower the temperature in cooling mode, your air conditioner will turn on and run until the house cools to that setting. The system does not heat or cool faster if you set the temperature higher or lower than you need—it just runs longer or shorter.

Changing the thermostat setting does not damage any part of your HVAC system. The thermostat is designed to be adjusted many times a day. Changing it frequently will not shorten the life of your furnace, air conditioner, or heat pump.

If you set the temperature very high in summer or very low in winter, your system will run continuously until it reaches that temperature. This will raise your energy bill but will not harm the equipment. Once the house reaches the target temperature, the system will cycle on and off normally to maintain it.

Thermostat settings that affect your heating and cooling costs

The single biggest factor in your heating and cooling costs is how many degrees away from outdoor temperature you set your thermostat. Every degree you lower the heat in winter or raise the cooling setpoint in summer saves roughly 1 to 3 percent on that month's heating or cooling bill, depending on your climate and how long the heating or cooling season lasts.

Using a programmable or smart thermostat to lower the temperature when you are away or asleep can cut your heating and cooling costs noticeably. For example, setting the heat to 62 degrees at night and 68 degrees during the day, instead of holding 68 all the time, can save 10 to 15 percent of your winter heating bill.

The fan setting also affects cost slightly. Setting the fan to "auto" (it runs only when the furnace or air conditioner is running) uses less energy than setting it to "on" (it runs constantly). If you want air circulation when the system is not heating or cooling, the cost difference is usually small—a few dollars per month—but "auto" is the more efficient choice.

Frequently Asked Questions

Will changing my thermostat setting void the warranty?

No. Changing the temperature, mode, fan speed, or schedule will not void your HVAC system warranty. Warranties cover defects in the equipment itself, not normal operation. Opening the thermostat case or altering internal parts could void the warranty, but adjusting the settings through buttons or screens will not.

Can I damage my furnace or air conditioner by changing the thermostat too often?

No. Your HVAC system is designed to turn on and off many times per day in response to thermostat changes. Adjusting the temperature frequently will not shorten the life of the equipment or cause any damage. The only cost is the energy used to heat or cool.

What is the difference between heat, cool, and auto mode?

Heat mode runs only the furnace or heat pump to warm the house. Cool mode runs only the air conditioner to cool it. Auto mode switches between heating and cooling automatically based on the temperature you set—if the house drops below that temperature, it heats; if it rises above it, it cools. Use auto in spring and fall when you might need both heating and cooling on the same day.

Why does my thermostat have a "hold" button?

The hold button (sometimes called "override" or "temporary hold") lets you change the temperature right now without erasing your schedule. When you press hold and adjust the temperature, the thermostat will stay at that temperature until you press hold again or until the next scheduled change. This is useful if you want a one-time adjustment without reprogramming the whole schedule.

Should I turn off my thermostat when I leave for vacation?

No. Turn the thermostat to a lower temperature in winter (around 55 degrees) or a higher temperature in summer (around 78 degrees) to save energy while you are away, but do not turn it off completely. Leaving the heat on at a low setting prevents pipes from freezing in winter, and leaving the cooling on at a high setting prevents mold and humidity damage in summer.