Learn about Cool to Dry

With Cool to Dry, Google Nest thermostats can use your air conditioner or heat pump to help reduce excessive humidity in very humid climates. This humidity control helps to prevent mold and maintain a healthier environment in your home. If your air conditioner has a dehumidification mode, your Nest thermostat can do even more to help reduce your home's humidity.

Cool to Dry can be used with any air conditioner or heat pump, but works differently depending on whether or not your system has its own dehumidification mode.

Note: Cool to Dry only works with air conditioners or heat pumps. If you have a standalone humidifier or dehumidifier, you won't find this option on your thermostat. Cool to Dry is available on the Nest Learning Thermostat 1st to 4th gen and the Nest Thermostat E.

Nest Learning Thermostat (4th gen) can automatically adjust your humidification setpoint based on the outdoor weather. For details, refer to Set up Humidity Helper on your Nest Learning Thermostat 4th gen.

Turn Cool to Dry on or off

• If your air conditioner doesn’t have a dehumidification mode, Cool to Dry is off by default. 
• If your air conditioner does have a dehumidification mode, Cool to Dry is turned on by default.
• You can turn Cool to Dry on or off on most thermostats or with the Google Home or Nest app.

On your thermostat

Note: This setting is only available on the Nest Learning Thermostat (3rd gen or earlier).

1. Press the ring to bring up the Quick View menu.
2. Select Settings.
3. Open Nest Sense.
4. Choose Cool to Dry.

Choose YES to enable Cool to Dry or NO to disable it.

Home app

1. Open the Home app .
2. Tap Favorites or Devices .
3. Select the thermostat that you want to control.
4. Access your thermostat's humidity settings:
   1. Nest Learning Thermostat (4th gen):
      Tap Settings Temperature preferencesHumidity HelperCool to Dry.
   2. All other thermostats:
      Tap Settings Temperature preferencesCool to Dry.
5. Tap the switch to enable or disable Cool to Dry.

Nest app

1. Select your thermostat on the app home screen.
2. Tap Settings .
3. Tap Nest Sense Cool to Dry.
4. Turn Cool to Dry on or off.

Check the current humidity

• On your thermostat: Press your thermostat’s ring to open the Quick View menu. Here you can find your home’s current humidity.
• In the app: Tap your thermostat. You’ll find the current humidity.

Change Cool to Dry humidity settings

On your thermostat

1. Press the ring to bring up the Quick View menu.
2. Open Settings.
3. Pick Equipment  Continue  Continue.
4. Select Dehumidifier  Set Humidity.
5. Choose the approximate humidity level you want your thermostat to target.

Home app 

1. Open the Home app .
2. Tap Favorites or Devices ..
3. Select the thermostat that you want to control.
4. Tap Settings Dehumidifier.
5. Tap the switch to enable the dehumidifier.
6. Tap the plus or minus buttons to set the approximate humidity level that you want.

Nest app

1. On the home screen, select the thermostat you want to control.
2. Tap Settings .
3. Select Equipment Dehumidifier.
4. Slide the button to set the approximate humidity level you want.
5. Tap the switch in the upper right to turn humidity control on or off.

How settings work

• To set an exact humidity percentage for your Nest thermostat to try to maintain, you will need to have a standalone dehumidifier set up in your thermostat.
• Cool to Dry will only cool your home to 3°F below your current set temperature when you are home, or 5°F lower when you are away and your thermostat is set to Eco Temperatures. This means Cool to Dry may not always reach a specific humidity level before it has to shut off.
• Because Cool to Dry may not always reach your target humidity, you’ll only be able to set an approximate target humidity level, represented by the number of water drops on your thermostat. That’s why you won’t find a specific percentage in your humidity settings.
• To set your humidity level, you can select from zero to three shaded water drops on your thermostat as your target humidity level to represent approximate humidity in your home. To turn humidity control off, select the empty water drop.
• If you select a low humidity level (fewer water drops) your system may need to run more frequently to keep your humidity low, which may use more energy.
• If you choose a high humidity level (more water drops) your system should run less often.

How Cool to Dry works

When Cool to Dry turns on, it will appear on your thermostat and in the Nest app.

• When you're home, Cool to Dry will turn on the air conditioner if your home's humidity rises above 70% and cooling is off.
• If you're away, and your thermostat is set to Eco Temperatures for 3 days straight, Cool to Dry will turn on the air conditioner if your home's humidity rises above 65%.

• Cool to Dry may not always be able to lower the humidity in your home. It will only cool your home a few degrees lower than your set temperature and it won't cool your home below 75°F while you're away or 80°F while you're home, even if your humidity is still high.

  If your Nest thermostat senses that the humidity isn't dropping over time, it'll shut off the air conditioner and return to your regular cooling schedule to avoid wasting energy. Below you can check how Cool to Dry can help keep humidity at healthy levels by periodically turning on the air conditioner.

• Cool to Dry will run your air conditioner in dehumidification mode as needed to reach your approximate humidity level.
• Cool to Dry will give your air conditioner a break every 10 minutes to prevent your air conditioner’s coils from freezing while lowering the humidity.
• If you’re home, normal use of your air conditioner will usually keep humidity levels below your approximate humidity setting.
• If your humidity levels rise above your target level and the air conditioner isn’t already running, Cool to Dry will turn on.
• When you’re away from home, Cool to Dry will turn on if your thermostat is set to Eco Temperatures and your home’s humidity rises above your target level.

Without Cool to Dry While you're away humidity levels rise into the High Humidity range when the air conditioner is off. This may allow mold to grow inside your home.
With Cool to Dry While you're away your Nest Thermostat cycles your air conditioner to keep humidity levels below 65%.

Check that your system has dehumidification mode

Follow these steps to view your system's wiring, and then check the thermostat's star terminal or AQ+ terminal (depending on your thermostat and your system) to find out if your cooling system has a dehumidification mode.

On your Nest thermostat

1. Press your thermostat's ring to open the Quick View menu.
2. Choose Settings Equipment.

Home app

1.  Open the Home app .
2. Tap Favorites or Devices ..
3. Select the thermostat that you want to control.
4. Tap Settings Thermostat  Wiring.

Nest app

1. Select the thermostat you'd like to check on the home screen.
2. Tap Settings .
3. Choose Equipment Wiring.

If there isn't a wire in the star connector or AQ+ terminal

Your air conditioner doesn't have a dehumidification mode.

If there is a wire in the star connector or AQ+ terminal, check the wire label.

• If the wire doesn't say dehum
  Your system does not have a dehumidification mode.
• If the wire says dehum
  Your system has a dehumidification mode or a standalone dehumidifier.

If you have a standalone dehumidifier, you won't find Cool to Dry in the settings. Your Nest thermostat will use your dehumidifier instead of Cool to Dry to help control the humidity in your home.

Check your system's manual or ask a pro

If you still need help determining if your air conditioner or heat pump has a dehumidification mode, look up your system's model number on the manufacturer's website, or check the manual. A local professional installer can also determine if your system has a dehumidification mode.

Systems that don't have a dehumidification mode

If you don't have a dehumidification mode on your air conditioner, you can still use Cool to Dry. Since your air conditioner converts hot humid air into cold dry air, Cool to Dry takes advantage of this and cycles the air conditioner on and off to lower the humidity.

When the Nest thermostat senses very high humidity, Cool to Dry automatically turns on the air conditioner. When Cool to Dry is on, your system may cool your home to a temperature lower than what you've set your thermostat to (up to 3°F lower than your scheduled temperature or 5°F lower than your Eco Temperatures).

Cool to Dry without a dehumidification mode can be expensive

If you use Cool to Dry with an air conditioner that doesn't have its own dehumidification mode, your air conditioner will run more often than usual, which can be expensive. If your air conditioner doesn't have a dehumidification mode, you should only use Cool to Dry if you live in a very humid climate.

If you already use your air conditioner to lower the humidity in your home by running it non stop, Cool to Dry can help you save money. Instead of keeping the air conditioner on all the time, Cool to Dry will cycle your air conditioner on and off while you're away, turning it on only when your humidity levels rise.

Systems that have a dehumidification mode

All air conditioners help dehumidify your home during normal operation. To cool the air, they pass it over refrigerated coils, which remove moisture from the air and condense it into water.

When your Nest thermostat controls an air conditioner with dehumidification mode, Cool to Dry works more efficiently to lower your home's humidity.

Air conditioners with a dehumidification mode provide more dehumidification than normal air conditioners by slowing down your fan speed. The slower fan speed allows for more dehumidification without overcooling the air in your home, but your air conditioner still needs to run.