Nest Support

Questions about Nest Learning Thermostat or Nest Protect: Smoke + CO alarm? We've got answers, videos, and plenty of resources to help you out.

What is Cool to Dry?

With Cool to Dry, the Nest Learning Thermostat uses your air conditioner (AC) to reduce excessive humidity and help create a healthier environment in your home, especially when you’re away. Cool to Dry can be expensive, so we only recommend it if your summers are very humid and you don’t have another, more efficient way to dehumidify your home.

If you live in a humid area, you already know that moisture in the air can cause mold to grow inside your home. This is especially true if you leave your house or vacation home unattended for a long time.

When the Nest Learning Thermostat senses very high humidity, Cool to Dry automatically turns on the air conditioner to lower the humidity to healthy levels. To achieve this, Cool to Dry may cool beyond the temperatures you set – up to 5ºF lower than what’s in your schedule or Away temperatures.

How does Cool to Dry work?

Your air conditioner chills air by passing air over refrigerated coils. These coils also take the humidity out of the air and turn it into water, which condenses on the coils. In other words, hot humid air goes in, and cold dry air comes out. So Cool to Dry lowers humidity without the help of a dehumidifier, by cycling the AC on and off.

When Cool to Dry turns on, you’ll see it on the Nest Thermostat display and apps:

While you’re home: Usually if you’re home, the temperature you set will keep humidity low without needing to turn on Cool to Dry. Cool to Dry will turn on the AC if humidity levels rise above 75%, and your cooling isn’t already on.

While you’re away: If your Nest Thermostat is set to Away or Auto-Away for at least three days, Cool to Dry will turn on the AC if humidity rises above 55%. According to the EPA, prolonged exposure to humidity levels above 55% could cause surface mold.

If Cool to Dry turns on while you’re away, you’ll see the Auto-Away symbol as well as Cool to Dry on the Nest Thermostat display and the Nest apps:

Cool to Dry will not always be able to get you down to 55% humidity. It has limits: Cool to Dry will only cool to 75ºF or 5ºF below your target temperature, whichever is higher.

If Cool to Dry senses that the humidity isn’t dropping despite its efforts, it’ll shut off the air conditioner and return to your regular schedule to avoid wasting energy for no reason.

Below you can see how Cool to Dry can help keep humidity at healthy levels by periodically turning on the AC.

Without Cool to Dry

in humid climates

With Cool to Dry

in humid climates

Will using Cool to Dry be expensive?

Cool to Dry may use more AC than you would otherwise, which can be expensive. For this reason, we generally don’t recommend using your AC as a dehumidifier. You should only turn on Cool to Dry if you live in a humid climate.

However, if you already live in an very humid climate, you may already be using the AC to lower humidity on your own. Often times that leads to running your AC non-stop while you’re home and away. If that’s your situation, then Cool to Dry could actually save money. Instead of keeping the AC on all the time just in case, the Nest Thermostat will turn it on selectively, only when you need it.

How do I turn Cool to Dry on or off?

By default, Cool to Dry is turned off in Settings. That means it won’t activate automatically if humidity reaches unhealthy levels.

If you want activate to Cool to Dry, go to SETTINGS > NEST SENSE on your Nest Thermostat or the Nest apps, and select Cool to Dry. The Nest Thermostat will ask you if it should use additional cooling to reduce high indoor humidity. Select YES or NO to turn Cool to Dry on or off.

How else can I lower humidity in my home?

Cool to Dry isn’t the only way to lower humidity. For very humid homes, a separate dehumidifier might be a good idea. For those without a dehumidifier, one of the easiest ways to keep your home from getting damp is to make sure the exhaust fans in bathroom is on when showering. You may also want to line drawers and closets with paper to keep moisture from accumulating on your walls.

You can also check the current humidity in your home on the Nest Thermostat or on the Nest apps. On the Nest Thermostat, the humidity is under SETTINGS > TECH INFO. On the apps, you can find the current humidity in SETTINGS > AT A GLANCE.

For more ways to prevent mold and high humidity in your home, please see the EPA’s handy guide, here.