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No, You Shouldn’t Set Your Thermostat to 85F. Here’s Why.

Recently, the federal government released new recommendations for energy efficiency. According to these federal guidelines, during the summer you should set your thermostat at 85F during the day when no one is home. They also recommended setting your thermostat at 82F at night.

Frankly, this is a bad idea. While setting your thermostat to these high temperatures in the summer might save you some money in the short run, in the long run it could be harmful to both your health and your home, not to mention being extremely uncomfortable!

Let’s take a look at why these extreme thermostat setbacks are a bad idea, as well as some ways you actually can increase your energy efficiency in the summer without sacrificing health or comfort.


Your Air Conditioner Has Two Jobs

Have you ever wondered why it’s called air conditioning instead of just air cooling? The reason is that your air conditioner doesn’t just cool the air. In fact, your home’s AC has two equally important jobs. The first is cooling, but the second is dehumidification.

When the warm air from your home passes over the evaporator coils, the air cools quickly and water in the air condenses on the coils. It’s just like water condensing on the outside of a cold Coke can on a warm summer day.

This removes humidity from the air, so that when the air passes through the supply vents back into your home, it’s both cooler and drier.



Setting the Thermostat Too High Prevents Dehumidification

Setting the thermostat at 85 saves energy because it causes the air conditioner to run less. A LOT less. And that’s the problem. If you set your thermostat in the 80s, the air conditioner won’t run enough to effectively dehumidify your home’s air.

Here in the Tennessee Valley, we have extremely humid weather in the summertime. If your thermostat is set at 80+ degrees, then the humidity inside of your home can easily get up above 70%.

That’s much higher than the recommended ideal indoor humidity of 30-50%. Having indoor humidity above 50% can cause serious issues for your health and your home.



The Dangers of High Indoor Humidity

Why is it important to keep your home’s humidity below 50%? One big reason is mold. Warm, humid conditions promote the growth of mold colonies. An 85F home with 70% humidity is basically a mold farm.

Having mold in your home can cause serious health issues. Mold spores can cause allergic reactions and worsen asthma symptoms. Even people without allergies or asthma can experience throat irritation, coughing, and other upper respiratory symptoms when exposed to mold.

Mold can cause damage to your home that requires expensive remediation and clean-up. And if it gets into your HVAC system, it can damage the ductwork and the HVAC unit, particularly the coils.

In addition to promoting mold, high indoor humidity itself can cause harm to your health. According to the National Weather Service’s heat index chart, an air temperature of 82F with 70% humidity results in a heat index—or “feels-like” temperature—of 86F. That’s in the “Caution” range for heat disorders caused by prolonged exposure.

In other words, just being in your house for several hours with the thermostat set at 82F as the federal government recommends could lead to you developing heat-related illness, like heat exhaustion. This is particularly true for people who are sensitive to the heat due to age or health issues.



Finally, high indoor humidity itself can also do damage to your home. When the humidity inside your home stays over 50% for a long period, it can cause swelling and warping of wood and paper products. This could damage hardwood floors or wood furniture, as well as causing damage to books and papers.


Save Energy Wisely

With all that said, it is possible to save energy during the summer without causing harm to your health or home. For instance, setting your thermostat to 78F during the day when no one is home can save energy while still keeping humidity under control.

Installing a thermostat that also monitors indoor humidity can also help to ensure that your air conditioner is running enough to keep the humidity below 50%. If your home’s humidity gets too high even with the AC running, then you may want to consider installing a whole-home dehumidifier.

Additionally, you can save energy by using fans to increase comfort. A ceiling fan can lower the perceived temperature of a room by up to five degrees, so you can keep the thermostat set a little higher when you’re home too.




Thermostat setbacks are a tried and true way to save energy. But if you set the temperature too high in summer, you can cause problems that simply aren’t worth the money saved. In fact, it could even cost you money in the long run. Moderate setbacks along with humidity control and the use of fans can increase energy efficiency without sacrificing your health or comfort.