How cool should my house be if it's 100 degrees outside?

Author: Merritt O'Conner  |  Last update: Wednesday, May 28, 2025

During heat waves, experts, including utility companies, recommend keeping your thermostat no more than 20 degrees cooler than the outdoor temperature. For instance, if it's 100 degrees outside, aim to set your thermostat to at least 80 degrees.

How cool should my house be when it's 100 degrees outside?

When outside temperatures are pushing 100 degrees, try setting your thermostat at 78-80 degrees. Supplement the indoor airflow with fans and other strategies to maintain cool temperatures inside.

What should I set my AC to when it's 110 outside?

Generally speaking, an air conditioner can only cool a room by 15-20 degrees, so if it hits 110, you can expect the AC to cool the room to 90-95 degrees.

How cold should AC be in 100 degree day?

On a 100-degree day, it is recommended to set your AC to around 78 degrees Fahrenheit for optimal comfort and energy efficiency. Setting the thermostat to this temperature helps keep your home cool without overworking your AC, which can help prevent refrigerant leaks and icy buildup.

How cool should house be compared to outside?

Simply put, it means you should never set your thermostat for a temperature more than 20 degrees cooler than the outside air. Why not? Most air conditioning systems can only handle a 20-degree difference between the outside and inside air temperatures.

AC is out its over 100 DEGREES OUTSIDE! Tempe Az

How cool should my house be if it's 90 outside?

What should my AC be set at if it's 90 degrees outside? If the outdoor temperature is 90 degrees, it's recommended to set your thermostat between 75-78 degrees.

Is 76 too high for AC?

What's The Ideal AC Temperature? Generally, when you are at home, your A/C's ideal temperature is between 76- and 78-degrees Fahrenheit. If you spend most of the day away from the house, set the thermostat a few degrees higher instead of cooling your home for no reason.

Is it normal for AC to run all day in 100 degree weather?

It's summertime, and you've noticed your AC never stops running. Should you be concerned? Here's the thing: It's normal for your AC to run continuously during hot summer months. You see, on extremely hot days—we're talkin' high 90s to 100s—your system needs to keep up with the incoming heat.

What should I set my AC to on a hot day?

Summer Air Conditioner Settings

In the summer, experts say the thermostat for your air conditioner should be set to at least 78°F during the day when people are at home.

How can I keep my house cool in 110 degree weather?

How to keep your home cool in hot weather
  1. Let in cool air and encourage air flow. ...
  2. Keep warmer air out during the day. ...
  3. Use a fan to enhance the breeze. ...
  4. Limit hot activities. ...
  5. Cool yourself down. ...
  6. Find an alternative space.

Does keeping the AC at 72 save money?

Best AC Temperature Settings While You Are Home

As you consider the most comfortable room temperature for your lifestyle and family, keep in mind that for each degree that you set your thermostat above 72 degrees, you can save up to 3% on your energy bill.

How long should an AC run to drop 1 degree?

On average, an air conditioner running in good condition should take about 15-20 minutes to drop the temperature by 1 degree in a standard-sized room. However, factors like outside temperature, unit size, and insulation quality can affect this timing.

What AC temperature is good for sleeping?

Sleeping in a room with the air conditioner set to an appropriate temperature is important for quality sleep. The ideal AC temperature for sleeping is around 65°F (18.3°C). However, this may differ between individuals, who might find their ideal AC temperature lies between 60 and 67°F (15.6 and 19.4°C).

How cool should my AC make my house?

78°F is generally considered a comfortable temperature for most people in a house, especially in warmer months. It balances comfort and energy efficiency. However, personal preferences and humidity levels can make it feel warmer or cooler, so adjusting slightly up or down may be necessary for optimal comfort.

Is it okay to not turn your air conditioner on in a vacant house it's 100% outside?

Key Takeaways. It's more energy-efficient to keep your AC on but set a few degrees higher when you're away from home for the day. Completely turning it off doesn't necessarily save energy as the unit will have to run longer to cool down a hot house upon your return.

What is the best cold temperature for a house?

Recommended Temperature When You Are Home

The World Health Organization (WHO) recommends setting your thermostat no lower than 64 degrees (F) in the Winter months while people are in the home. If there are infants or elderly individuals, they recommend keeping the temperature at 70 degrees at a minimum.

Is 72 too cold for AC?

While the standard room temperature of 72 degrees Fahrenheit is commonly favored by many, others argue for higher settings, particularly when it's hotter outside.

How much should AC run on hot day?

On an average summer day, a general guideline is that your AC should operate between 12 and 16 hours. However, several factors can influence this, including the outdoor temperature, desired indoor temperature, the size and type of your unit, and your home's energy efficiency.

Is 68 too low for AC?

During a heatwave, we recommend that you don't lower the AC's setting below 68°F. This is already quite chilly for most people, and many would consider it too cold. An air conditioner set this low risk of its coil freezing—and that's bad news because it indicates that the air conditioner is overworked.

What should I set my AC to when it's 100 outside?

During heat waves, experts, including utility companies, recommend keeping your thermostat no more than 20 degrees cooler than the outdoor temperature. For instance, if it's 100 degrees outside, aim to set your thermostat to at least 80 degrees.

Is it a bad idea to run in 100 degree weather?

Understand heat index dangers: Avoid running outside if the heat is above 98.6 degrees and the humidity is above 70-80%. If the humidity in the air is so high that it prevents the process of evaporation of sweat from the skin, you can quickly overheat and literally cook your insides from an elevated body temperature.

How low can I set my AC on a 100 degree day?

For the most efficient performance, set the thermostat 20 degrees lower than the temperature outside. On a 100℉ day, set it to 78℉ to 80℉ to manage utility costs. If there's a lack of airflow, the filter may need to be changed or AC vents cleaned.

How cool should my house be if it's 110 outside in summer?

Just because the outdoor temperature is above 100, the Ideal temperature to set your AC unit to doesn't change — it's 78 degrees. Higher temperatures in the home are to be expected when the weather is hotter than usual, but your thermostat can still be set the same as if it were a lower temperature outside.

Why is my AC set to 74 but reads 78?

If the temperature is set to 74°F but the thermometer shows 78°F, you will have to recalibrate the thermostat to account for this 4-degree deviation. Even with older AC units or furnaces, you might have to recalibrate your thermostat from time to time.

How much can AC cool in 100 degree weather?

So when we are having average temperatures, you should have no problem cooling to 70º or 71º if you like. However, when we approach 100º or above, you will likely be doing good to cool to 80º.

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