What is the 20 degree rule for AC?

Author: Darrick Torp  |  Last update: Wednesday, February 11, 2026

The “20-degree rule in air conditioners” is simple: don't set your AC more than 20 degrees cooler than the outdoor temperature. This guideline helps your system run efficiently and prevents overworking. In this article, discover why this rule is vital for your AC's performance and how to follow it effectively.

What is the best temperature for AC to lower bill?

A more moderate setting like 24°C (75.2°F) can achieve comfort with reduced electricity usage.

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

When temperatures exceed 100 degrees Fahrenheit outside, setting your air conditioning (AC) to around 75-78 degrees Fahrenheit is generally considered efficient. Here are some reasons for this recommendation:

Is 72 a good temperature for air conditioning?

Setting your air conditioning to 72°F is generally considered a comfortable indoor temperature for many people. It strikes a good balance between comfort and energy efficiency, making it a popular choice for residential settings.

How long should it take to cool a house from 90 to 72?

Cooling a house from 90 degrees to 72 degrees typically takes about 2 to 4 hours, depending on various factors.

Lower your air-conditioning bill with the 20 degree rule

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.

Is 72 degrees to hot to sleep in for a house?

Sleep experts believe the best temperature for great sleep is between 68-72 degrees Fahrenheit. But in addition to making you uncomfortable and interfering with healthy sleep patterns, being too hot at any time of day or night can cause health risks like dehydration and heat stroke.

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.

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.

Why not set the thermostat at 72?

Setting the thermostat below 72 degrees while using an air conditioner can cause the unit to work harder than necessary, leading to higher energy bills and potential damage to the appliance.

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.

Should my AC keep up on a 100 degree day?

It's true that air conditioners do have limits when the outside temperature is extreme. This means that your air conditioner may be able to keep your home at 77 or 78 degrees when it is 104 degrees outside.

What temperature do most people keep their house at in the summer?

The average summer temperature is around 71°F. In winter, this falls just a touch to 70°F. Here's a winter breakdown for thermostat settings across the U.S., according to the survey participants: 47% set it between 68°F and 71°F.

How do I keep my AC bill low?

10 Ways To Reduce Your Air Conditioning Costs This Summer
  1. Running ceiling fans. ...
  2. Plant big shade trees around your house. ...
  3. Install a smart thermostat. ...
  4. Thermostat placement. ...
  5. Think about your basement. ...
  6. Seal off any leaks. ...
  7. Evaluate your home's insulation. ...
  8. Regularly service your AC.

What is the best AC temperature for sleeping?

The best AC temperature for sleeping

The goldilocks zone: Aim for a temperature between 18°C (64°F) and 22°C (72°F) for optimal sleep comfort. Individual needs: Consider personal preferences and adjust the temperature accordingly. Some people may prefer slightly cooler or warmer settings.

Which AC is best for an electricity bill?

A 5 star AC offers superior energy efficiency, leading to lower electricity bills, while a 3 star AC is more budget-friendly but tends to consume slightly more power. If you're undecided on whether to go for a 5 star or 3 star AC, consider factors like long-term energy savings and initial costs.

Is it OK for AC to run constantly on hot day?

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. To do that, it will run longer in order to maintain a constant, desired temperature in your home.

Is $12,000 btu too much for a bedroom?

You also don't want to buy a model that's too powerful for a room. Sure, a 12,000-BTU air conditioner will cool a small space (150 square feet or less) quickly. But it might cool it too quickly, preventing it from removing some of the ambient humidity from the room and leaving the room damp.

What temperature do most people set their AC at?

The average air conditioning temperature depends on a variety of factors, including geographic location, comfort levels, season, and cost of energy. Anywhere between 72° to 78°F is typically standard. A study in Texas revealed that the model temperature during summer months was between 70° and 75°F.

What is the cheapest temperature to keep AC on?

Finding the right AC temperature for your electricity bill is a balancing act. By setting it around 78°F and considering external factors, you can enjoy comfort and save on energy costs simultaneously. Remember, small adjustments can lead to significant savings over time.

Should my thermostat be on run or hold?

The best way to save money is by combining both. The “run” feature lets you preset the temperature when you're not home to prevent wasting money on cooling or heating an empty home. Meanwhile, the “hold” button lets you change the room's temperature without changing your energy-saving, preset schedule.

Is it expensive to leave the AC on all day?

Leave Your Air Conditioner On

You might think you're saving money by turning your AC off when you step out of the house. However, a wave of heat and humidity can sneak into your home in the interim. Therefore, leaving your air conditioner on all day in hot temperatures is more energy efficient.

What is the healthiest temperature for a bedroom?

The best room temperature for sleep is approximately 65 degrees Fahrenheit (18.3 degrees Celsius). This may vary by a few degrees from person to person, but most doctors recommend keeping the thermostat set between 65 to 68 degrees Fahrenheit (15.6 to 20 degrees Celsius) for the most comfortable sleep.

How to survive hot summer nights without AC?

If the summer temperatures have you needing to chill out, try our tips.
  1. Open your windows at night. ...
  2. Close your window coverings. ...
  3. Insulate and air seal your home. ...
  4. Bake and wash at night. ...
  5. Fire up the grill! ...
  6. Install an exterior window shade. ...
  7. Use your fans in the right places. ...
  8. Use your exhaust fans.

What is the perfect sleeping position?

According to Chester Wu, MD, a psychiatrist and sleep expert, one of the best sleep positions is side-sleeping. “This position is ideal as it helps maintain proper spine alignment, reduces snoring and sleep apnea symptoms, and is beneficial for digestion and heart health,” said Wu.

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