# Thermostat reading the wrong temperature: how to fix it

Updated: 2026-10-24 · https://pros411.com/en/guides/hvac/thermostat-wrong-temperature

## Short answer

Look around the thermostat first. A lamp, a TV, sunlight, a kitchen or a vent blowing on it makes it read warmer or cooler than the room. Move the heat source away, then tape a simple thermometer next to it and compare after 15 minutes. Put in fresh batteries. If it is still off by more than two degrees, use the temperature offset in its settings or call a technician.

## How to fix a thermostat that reads wrong

![Cartoon thermostat reading 75 degrees because a lamp heats it, while the furnace and the cat shiver](https://pros411.com/img/guias/thermostat-wrong-temperature.webp)

1. **It says warm, the room feels cold.** It reads 75° and you are in a sweater. Often the thermostat is right about its own spot, just not about the room.
2. **Move heat sources away.** Lamps, TVs, sunny windows and space heaters warm the thermostat, so the furnace shuts off early. Move them away or close the blinds.
3. **Compare with a thermometer.** Tape a simple thermometer to the wall next to it, at the same height. Wait 15 minutes and compare the two numbers.
4. **Put in fresh batteries.** Weak batteries can make a digital thermostat act strange. Pull it gently off the wall plate and replace them.
5. **Right number, warm room.** Still off by more than two degrees? Many thermostats have a temperature offset in the settings. Check the manual, or call a technician.

## Why it happens

A thermostat measures the air right where it hangs. Sun, lamps and electronics make it read high. A drafty outside wall, a door to the garage or the hole behind it where the wires come through make it read low. Dust inside, an old thermostat that is not level or a failing sensor can also throw it off.

## Good spot, bad spot

- Good: an inside wall in a room you use, about five feet off the floor.
- Bad: near a sunny window, an outside door, the kitchen or a bathroom.
- Bad: right under a supply vent, or near a lamp, a TV or a radiator.
- Moving a thermostat means running new wires through the wall. That is a job for a technician.

## When to call an HVAC technician

- It is still off by more than two degrees after you move heat sources and replace the batteries.
- The reading jumps around, or the furnace turns on and off at random.
- The thermostat sits in a bad spot and needs to be moved.
- One room colder than the rest stays cold even when the reading is right.

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## Frequently asked questions

### Why does my thermostat show the wrong temperature?

Usually something near it, like sunlight, a lamp, a TV or a draft, warms or cools that spot. Weak batteries, dust or a failing sensor can also throw it off.

### How do I know if my thermostat is reading correctly?

Tape a simple thermometer next to it at the same height and compare after 15 minutes. A degree of difference is normal.

### Can I calibrate my thermostat?

Many digital thermostats let you add or subtract a few degrees with a temperature offset or calibration setting. Look for it in the manual or the settings menu.

### Where should a thermostat be placed?

On an inside wall of a room you use often, about five feet off the floor, away from sun, vents, doors and the kitchen.

### Why is my house colder than the thermostat setting?

The thermostat may be warmed by a heat source, or the furnace may not keep up. Check the thermostat first, then the filter. If the furnace runs nonstop and the house stays cold, call a technician.