Why your Nest thermostat temperature and your home temperature can be different
When your system and thermostat are working normally, there can be a small difference between what the app and your Nest thermostat show and the temperature you feel. For instance, there may be a small temperature swing because Nest thermostat will wait to turn on your system until it gets to about 1ºF (0.5ºC) cooler than the temperature you’ve set. This is to prevent unnecessary wear on your system and help save energy.
- If your home is very cold and you need to troubleshoot a problem with your thermostat or system, you can turn heating on manually before you troubleshoot.
- If you notice a difference of a few degrees between what your thermostat says and how warm or cool you feel, your thermostat and system are probably working normally. Here are some reasons why.
The temperature on your thermostat looks wrong
Your thermostat’s temperature screen will often show you two different temperatures:
- The large target temperature (A) in the middle of the thermostat screen is the temperature that your thermostat was set to either manually or automatically by your temperature schedule. Your system will work to reach and maintain this temperature.
- The small current temperature (B) at the edge of the thermostat screen is the ambient temperature in your home right now.
Note: If your system is on, you’ll also see the estimated time (also known as Time-to-Temperature) it will take for your home to reach the target temperature.
Nest Learning Thermostat
Nest Thermostat E
If you have Farsight enabled
3rd gen Nest Learning Thermostats can use Farsight to show you useful information when you approach. You can have Farsight show you either the target temperature or the current room temperature. If the room seems cooler or warmer than what your thermostat says, Farsight may be set to show you the target temperature, not the current temperature in your home. You can change Farsight settings any time you like.
There's a short delay for turning on your system
It’s normal for your home’s temperature to vary slightly above or below the temperature set on your thermostat for a short while. This is often due to the built-in delay for turning on your system. This delay is commonly called the maintenance band, deadband, differential, or temperature swing. The delay is usually just a few minutes, but it’s there to help you and your system:
- Many heating systems have a built-in delay to prevent excessive wear. Since there are moving parts, turning your system on and off frequently may shorten its lifespan.
- Nest thermostats also have a built in delay, like many other thermostats. This is to help save energy and also prevent system wear, especially for systems that don’t automatically delay turning on.
- The maintenance band delay allows the temperature in your home to change by a few degrees before turning on your system, but in most cases you should still be comfortable.
- You’ll know that your thermostat is set to turn on your system by the color of the screen. For example, if the screen is orange, your thermostat is trying to turn on your heat. You’ll also see the temperature screen change color in the app.
How the maintenance band's heating delay works on Nest thermostats
- The maintenance band for heating is 0.4°C above and below the target temperature.
- The Nest thermostat maintenance band is not adjustable.
- Your thermostat will switch your system on when the room temperature is about 0.5°C away from the set temperature, then it’ll run your system until the temperature is slightly beyond the target temperature that you’ve set.
- The Nest thermostat's minimum on-off times are five minutes for heat pumps and air conditioning systems and three minutes for conventional heating systems (like furnaces and boilers). The Nest thermostat uses these minimum on-off times for all temperature changes in its schedule.
Example of how the maintenance band works
Let’s say your Nest thermostat is set to heat your home to 21°C. Here’s what will happen:
- When the room cools down to about 20.5°C, your thermostat will turn on your heating. The heater will start heating your home. It might take a few minutes for the pipes, ducts, or radiators to warm up.
- Your Nest thermostat will keep running the heat until the room temperature reaches about 21.5°C. Then it will turn off the heat.
- If you have a forced air system that uses a fan, the fan might continue to run for a while after the system has turned off to continue pushing warm air through the vents.
- If your system uses radiators, they might stay warm for a while and continue to warm the room. Your thermostat can use True Radiant to correct for this over time.
- If it's cold outside, the room temperature will eventually start to fall again, drop past 21°C to 20.5°C, and the cycle will repeat.
Your new Nest thermostat may still be learning
It can take some time for your thermostat to learn your heating schedule as well as how quickly your home heats up and cools down. So, for the first few days you have it, you’ll need to teach your thermostat what temperatures you like and when. Just turn the temperature up or down on your thermostat or with the app.
If you’ve had your thermostat for a while and it still seems like it’s getting too hot or too cold, try some of the troubleshooting steps below.
Nest thermostats display a rounded temperature
The temperature you see on your Nest thermostat screen and in the app is rounded to the nearest 0.5°C. Your thermostat uses the unrounded temperature to determine when to turn on your system. So the temperature you see on your thermostat or in the app might change by a few degrees before your system turns on.
That said, all Nest thermostats have multiple temperature sensors that take very precise readings. You can see the unrounded ambient temperature (to the tenth of a degree) : on your thermostat, go to Settings Technical Info Sensors.
Your home takes time to warm up and cool down
Your system may take a few minutes to start after your thermostat tells it to. Once your system starts, it may take a few minutes to warm or cool the air near your thermostat or active temperature sensor. During that time the room’s temperature can drift beyond the maintenance band.
Some systems continue running for a short time
Some systems may continue to heat or cool for awhile after they’ve been turned off.
Some systems continue to run the fan to circulate the air that’s left in your ducts or the radiators might stay warm for a while and continue to warm the air in the room. This can cause the temperature to change slightly even after your thermostat stops and cause the temperature in your home to slightly exceed the maintenance band.
Your thermostat is in a warm or cool spot
Location is one of the most common reasons for a small temperature difference. For instance, if your thermostat is in a hallway near the front door, cold air drafting from outside will make it think it’s cooler inside.
If your thermostat is wall mounted, it may be on a wall that’s typically cooler or warmer than the rest of your home. In a poorly insulated or uninsulated wall, warm or cool air may be flowing behind your thermostat. You can patch up or plug this hole to help reduce airflow behind your thermostat. Consult your local building code for materials that you can use to patch this hole safely.