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What Temperature Should You Leave Your Air Conditioner On During A Heat Wave?

Air conditioning systems experience many issues if set at very low temperatures during an extreme heat wave. Lowering your thermostat does not increase your air conditioner’s effectiveness when temperatures cross 95 degrees Fahrenheit. Instead of throttling down your thermostat, a comfortable, desired temperature like 72 degrees Fahrenheit is ideal to leave your air conditioner on during a heat wave. The unit operates more efficiently at this level compared to a very low thermostat setting that will stress it. 

According to National Public Radio (NPR), an organization aiming to create a more informed public, air conditioner systems keep indoor temperatures only 20 degrees cooler than outdoors. I formerly worked in Texas in a region where the outside temperature soared above 120 degrees Fahrenheit. I habitually lowered the thermostat of my AC system on hot days to create a comfortable environment inside the home. But the temperature inside never dropped below 78 – 80 degrees, leading me to further throttle my thermostat to its lowest setting. 

Since everyone in the neighborhood shared the same idea, overloaded power grids caused a power outage. It took three days for the utility company to repair it. I also noticed that my utility bills were much higher during the summer. The HVAC technician who serviced my unit a week later reported clogged air filters and plenty of debris on the exterior unit fan.

Let’s walk through the operating principles of air conditioners, the major issues they face during a heat wave, and how you can prepare your unit to perform efficiently in the summer. We will compare variable-speed compressors and single-speed compressors and explore other, simpler techniques to keep your home cool in the hottest months of the year. 

Operating Principles Of Air Conditioners

heat wave

The scientific principles of an air conditioner are complex. But I will keep it simple enough so you can understand how to operate it during a heat wave. AC systems use a refrigerant that absorbs hot air from inside your home. This substance is pushed through a device called a compressor. The compressor pressurizes it and moves it to the outdoor unit, where a condenser coil condenses it into liquid form, giving out hot air. A fan blows the hot air out.

The liquid refrigerant then passes through a metering device that checks the temperature in your home and compares it to the temperature you wish to achieve. This determines how much work the system has left to achieve the desired temperature. The next step moves the refrigerant through an evaporator, where fans blow air over it, changing its pressure. The refrigerant reacts by absorbing the surrounding energy and heat, causing it to boil. This causes the air around it to cool while the fans blow this chilled air into the indoor space. 

The process is repeated until your AC unit achieves the temperature level you set on your thermostat. During an extreme heat wave, your AC system works harder to remove large amounts of heat from inside your home. To prevent it from getting overloaded, you must avoid setting very low temperatures on your thermostat to reduce the work done by the system.

AC Issues During A Heat Wave

I have experienced several issues in my AC system during heat waves. Here are some common ones:

  • I used to run my air conditioner for long periods during the hot summer, causing the air filters to get clogged faster than usual. 
  • Due to large and continuous workloads, the fan on my exterior unit accumulated more debris.
  • Setting my thermostat to its minimum level could still not achieve a cooler indoor environment. Instead, I had higher utility bills compared to the non-summer months. 

My early lessons transformed me into a passionate HVAC hobbyist. I have spent hours researching optimization techniques and advising people on how to get the best out of their AC systems. In the next section, I will give simple tips for preparing your air conditioner for an extreme heat wave.  

Preparing Your Air Conditioner For A Heat Wave

heat wave

Follow the steps below to prepare your air conditioner for a heat wave.

  • Set your thermostat to a comfortable level and let your system continue running. I set my thermostat to 72 degrees Fahrenheit when the outside temperature is very high. While this helps me achieve temperatures no lesser than 78 degrees inside my home, it still keeps me comfortable enough. Setting the thermostat very low stresses my AC system and does not manage to lower the temperature any further.
  • Extreme weather conditions take a heavy toll on your air filters. Replace the air filters on your air conditioner at least once a month.
  • Clean the fans on your exterior unit periodically with a long-handled brush. You must do this only when your unit is turned off.
  • Aim your lawn sprinklers at your outside unit to reduce the temperature of your refrigerant. I have noticed that this will lower the internal temperatures of your unit by about 10%. 
  • Older AC systems lack the technology to operate efficiently in extreme weather. If your system is over 12 years old, consider replacing it with a newer, more efficient model.

Other Ways To Keep Your Home Cool

I reduce the impact of extreme hot weather on my AC system by employing other methods to keep my home cool. Here are the most common methods I use to cool my home during extreme summer months.

  • Stoves, dishwashers, ovens, and lights emit large amounts of heat. I turn these off during hot parts of the day to reduce heat in indoor areas.
  • The ceiling fan is a great alternative that can cool indoor areas and reduce stress on your AC system. 
  • I use dark window shades to reduce the sunlight inside my home.
  • I use the AC system to cool down my house as much as possible during the night with less indoor heat. This reduces the air conditioner’s workload as heat builds up in the morning. 
  • I recommend planting trees around your home to create shade if you have the space. This long-term, natural cooling system, coupled with better insulation, will improve the performance of your AC system. 

Benefits Of Installing An Automatic Delay Fan Switch

Modern AC systems use an automatic delay fan switch to maximize the energy consumed by the unit. The fan switch enables your air conditioner to operate a few more minutes after the compressor switches off. This forces the cool air left in the ducts after a cooling cycle into the indoor area. 

In a traditional system, the cool air collected in the ducts after each cooling cycle is wasted. So, the energy utilized to create this cool air is also wasted, reducing the AC unit’s overall efficiency. Systems with an automatic delay fan switch enjoy more time between cooling cycles as your home receives more cool air from each cycle. This means higher efficiency, lower utility bills, and better health for your AC unit. It doesn’t get better than that, does it? 

Variable Speed vs. Single Speed Compressors

heat wave

Wondering whether you need a single or variable-speed compressor? Here is a comparison to assist you in making your choice: 

 Single-Speed CompressorVariable-Speed Compressor
OperationThey can operate only at a single speed–0% or 100%.They can operate at different speeds when the outside temperature gets very high.
BenefitsSingle-stage compressors operate with more frequent on/off cycles.
Short cycles result in uneven distribution of air throughout your home.
Shorter runtimes reduce the unit’s ability to remove humidity from the air.
Variable-speed compressors can run at a lower setting for longer periods with fewer on/off cycles.
Longer cycles result in better air circulation.
Longer runtimes enable the system to remove more humidity from the air inside your home.
CostAn AC unit with a single-speed compressor is inexpensive to purchase with low installation costs.Variable-speed AC units are more expensive than single-speed units.
Higher efficiency results in lower utility bills that can reduce your long-term costs.

A variable-speed system is the right choice unless you are on a tight budget and want a cheaper upfront cost. With higher efficiency resulting in lower utility bills, this is a great long-term investment that can save you a lot of trouble during the extreme summer months.


The next time you battle a heat wave, remember to set your thermostat at a reasonable level and reduce heat from other sources in your home. If you want a new system, consider investing in an AC unit with a variable-speed compressor and an automatic delay fan switch. Following the best practices I shared in this article, your system should operate without overload and enjoy a long lifespan.


What temperature should I leave my air conditioner on during a heat wave?

Set your thermostat to a comfortable level and let your unit run continuously on it. Any level between 72°F and 75°F should keep your unit running smoothly without getting overloaded. Never throttle the thermostat to a very low level, as this will overwork the unit, increasing your utility bills and clogging your air filters while not cooling your interior further. 

How do I prepare my air conditioner for a heat wave?

Follow the simple steps below to prepare your air conditioner for a heat wave.

  • Set your thermostat to a comfortable level between 72-75°F and let it run continuously at this level. Don’t throttle your thermostat to very low levels.
  • Replace air filters on your air conditioner regularly during heavy use.
  • Clean the fans on the exterior unit periodically.
  • Aim your lawn sprinklers on the outside unit to reduce the system’s temperature.
  • Replace AC systems older than 12 years with more efficient ones.
  1. What are other ways to keep my home cool?

Five simple ways to keep your home cool and reduce stress on your AC unit.

  • Switch off appliances like ovens, stoves, dishwashers, and lights during hotter parts of the day to reduce the work for your AC unit.
  • Use ceiling fans to keep indoor areas cool.
  • Use dark window shades to reduce the sunlight which creates more heat in indoor areas.
  • Use your AC to cool down your house as much as possible at night to reduce the work required after sunrise.
  • Plant more trees to create shade over your house and reduce indoor temperatures.

What are the benefits of installing an automatic delay fan switch?

An automatic delay fan switch maximizes the energy your air conditioner unit consumes. Cool air left in the ducts is moved into your room by allowing the unit to operate a few minutes after the compressor is shut off. The switch increases the interval between cooling cycles by utilizing all the cool air the unit generates in each cooling cycle. 

How does a variable-speed compressor increase the efficiency of my air conditioner?

A variable-speed compressor enables your air conditioner to operate at lower levels for longer. This increases the efficiency of your system. Single-speed compressors can operate only at 0% or 100% and have a higher frequency of on/off cycles. Variable-speed systems have better air circulation and remove more humidity from the air. Single-speed systems are inexpensive with lower installation costs. While variable-speed systems are more expensive, they lower utility bills and reduce long-term costs.


  • Alanna Greene

    Alanna is an avid traveler who lives in Michigan. In addition to writing for Temperature Master, he also sells crafts on Etsy and takes long walks through the forests near her home.

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