Setting your Thermostat for Air Conditioning in Hot Weather

Here in the mid-Atlantic and Northeast, the temperature has been getting up into the high 90’s (Fahrenheit) in recent days, and the forecast is calling for 2 to 3 days with highs at or above 100 here in Delaware.  What is the best way to set your thermostat for air conditioning when the weather is this hot outside?  In this post I will demonstrate that setting the thermostat higher in hotter weather will not only save energy and money (which is obvious), but is also better for your health and enjoyment of life.

To illustrate why this is true, I will start by sharing an amusing story about Texans.

Texans and Air Conditioning:

I grew up in Lancaster, Pennsylvania, which has humid summers with occasional hot spells up into the upper 90’s.  But these hot spells are not the norm.  The climate overall is quite temperate, and it is common for people, like me, to grow up without air conditioning.  During these few hottest days of summer, we slow down, avoid heavy exertion during the heat of the day and stay indoors or in the shade, drinking cool drinks and maybe using a fan.

Star in a Round Dome of a Ceiling

The star in the dome of the capitol building in Austin, Texas.

Texans pride themselves on being bold and courageous.  One summer, I took a vacation to Austin, Texas, which, at the time, was the farthest south I had ever been.  The sun was much brighter, and the days were hot, all in the 90’s.  But I was shocked to find that Texans were wimps about the heat.  They complained that it was too hot out even early in the day, when it was still in the 80’s, and when it was dry heat.  Why were these “tough” Texans such cowards about the heat?  Because they all were used to having air conditioning virtually everywhere.  They had never learned to adapt, and never allowed their bodies to adapt to the heat either.

The Human Body Adapts to Heat & Cold:

The human body, like most biological systems, has a remarkable ability to adapt to different conditions.  Humans have lived for thousands of years in virtually all parts of the globe, from tropical rainforests to the driest deserts to frigid polar areas and everything in between.  People who work outdoors in the deep south do not complain when faced with a modestly warm, 85 degree day in the mid-Atlantic, the same way someone from Alaska, Maine, or Minnesota doesn’t complain when the temperature drops below 20 degrees.  But in order to allow yourself to adapt, you need to actually expose yourself to the weather.  If you set your thermostat to 68 degrees in the summer and stay indoors most of the time, when you step outside into 85 degree weather, it’ll feel like a sauna.  If your thermostat had been set at 80 instead, you’d walk outside and it would feel a little bit warm.

Remember to stay adequately hydrated:

It is very important in hot weather to drink enough water, and if you are sweating a lot, to replenish your electrolytes by eating something that naturally contains some sodium and potassium.  Dehydration is the main health risk associated with very hot weather; imbalance of electrolytes is less common but is still an issue in very hot weather.

Adapting your behavior to the heat:

In addition to your body adapting on its own, there are easy ways to make the heat more tolerable.  People in the northern U.S. often make fun of southerners because they walk so slowly, but slowing down is one of the best ways to keep cool.  Drinking cool drinks, and wearing light, loose-fitting clothing that breathes well (like cotton or linen).

The best way to set your thermostat is relative to the outdoor temperature, not at a fixed temperature:

When it is 90 outside, try setting the thermostat at 80 or higher.  If it’s 95-100, try setting the thermostat at 85 or higher.  If you use a window unit without a temperature gauge, you can still use the suggestion below of inching the setting cooler gradually.

Hand Setting Thermostat at 82 degrees

82 feels cool when it's in the 90's outdoors.

Turn your A/C off when you leave your house or apartment, and close the blinds to keep the sun from heating up the interior.  When you return, if it’s too hot, inch the temperature down 1 or 2 degrees at a time until you feel comfortable.  This allows you to keep the temperature as high as possible.  You may be surprised at how much a difference of as little as 2 degrees Fahrenheit makes: air conditioning also dries out the air, so if you are coming in from a humid outdoor environment, the same temperature in an air-conditioned interior will feel much cooler.

Setting the thermostat very low (68 or 72 as some people do) in the hottest weather is not only costly and wasteful of energy, but it also is hard on your body and will keep you from appreciating the outdoors during hot weather.  Like the Texans described above, you risk becoming a wimp about the hot weather.  If instead you pick a more moderate temperature, you will not only be conserving energy (and saving money) but you will feel less of an adjustment when you go outdoors in the summer–and you will be more ready to appreciate outdoor activities, whether you do them in the heat of the day or during the cooler periods in the morning or evening.

What can you do?

  • Spend some time outdoors in the hottest weather (staying adequately hydrated!), to allow yourself to adapt to the heat.  You may find that the more time you spend in the heat, the less cool you need it to be indoors in order to feel comfortable.
  • Try experimenting with inching your thermostat or A/C settings down gradually from whatever interior temperature you are starting with, instead of just setting it at a cold, fixed level.  You may be pleased both with your savings on the electric bill, and your increased ability to enjoy the outdoors during hot weather.
  • If you are in charge of an office environment, consider setting the thermostat higher on the hottest days; make the dress code allow options for weather-appropriate clothing (shorts, skirts, sandals, short sleeves) on these days even if you require less casual attire on other days.  Let people know ahead of time what the interior temperature will be so they can plan accordingly.  If you are not in charge of the thermostat or dress code, voice your opinion to those who are in charge, and let them know that you would appreciate a more moderate indoor temperature in the interest of health and sustainability.
  • If stores, classrooms, or other indoor public spaces are too cold, let people in charge know, and encourage them to set the temperature to a more moderate level in the hottest weather.
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8 Responses to Setting your Thermostat for Air Conditioning in Hot Weather

  1. Tracy says:

    I agree Alex! Another great way I’ve found to keep cool is to simply dab some cold water on pulse points (wrists, inside elbows, neck) every hour or so. Helps a lot.

  2. watershedmg says:

    This is great! I noticed that too when I visited Texas, that everyone loves their 68-degree AC. I think it is silly to have it so chilly inside you need long sleeves when it’s so hot outside. Here in Tucson, when it is 108 degrees (and dry), it feels great to walk into an 85-degree room.

  3. zorach says:

    Thanks for the replies!

    Dabbing cold water can definitely make a big difference too, especially in dry air, but even when the air is fairly humid.

  4. niceartlife says:

    These are great suggestions zorach, thanks they are of great use! I never like extremes in temperature between the AC inside and the outside temperature. Very bad for the human body too indeed. Great article!

  5. Grant says:

    I went this summer with no AC living in Jersey. I used to hate hate hate the hot weather, and even though I’m still not super fond of it I do notice I can tolerate it a lot better this year than I usually do.

    One note about the “if you are in charge of an office environment” point, this piece of advice is not for those who work in office buildings, as the AC in office buildings is left on 24/7 to prevent the windows from blowing out.

  6. Anonymous says:

    This is a case of “your mileage will vary”. I don’t adapt well to hot weather. The only way I would live in a hot climate place (like Florida) is if I’m the CEO of a business that involves a cold product, like a liquid oxygen plant or ice making plant. That way, if the office A/C breaks, I could use my company’s own product to keep cool. :) I recently came close to having to move to Missouri, a hot climate place. I was considering what I’d do to modify my car for improved A/C onboard. I once lived in Orlando FL for a year straight. I absolutely hated the climate. They can keep the 3 month hot spell they call “summer”.

  7. Bill says:

    I just moved to Dallas and the temperture has been in the 90s and I haven’t yet turned my air conditioner on. My question is this, will I travel for weeks at a time. Will I be harming my home if I leave the air conditioner off and it gets to the 90s or above inside?

    • Alex Zorach says:

      It depends what is in your home, but in general, this will be fine. Some houseplants can be sensitive to heat, and some substances can melt, but most common household items will be fine. You can put anything in question (like chocolate bars, or anything made of wax with a low melting point) in the fridge. Many houseplants, especially cacti and succulents like a jade plant, can take prolonged extreme heat and drought, but ones that are less drought tolerant will dry out much faster in hot conditions.

      One other thing to check is any electronic equipment that generates waste heat. I’d unplug anything with an A/C adapter, especially things plugged in under a tightly-enclosed space like a computer desk. Not only will this save energy and keep the heat down, but it avoids the risk of equipment being damaged by the heat.

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