In short, the 20-degree rule of air conditioning states that you should always keep your AC unit at no more than 20 degrees lower than the outside temperature. It means that, if the outdoor conditions are at 95 degrees, you should set your thermostat at no less than 75 degrees.
A common rule of thumb is that most models can function properly only above 68 degrees Fahrenheit. Any lower temperature will result in the system freezing up. In addition to a frosty refrigerant, the piping and coils could also become covered with ice.
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.
68 degrees isn't a recommended temperature to keep as a setting for your air conditioner. The refrigerant in the AC doesn't absorb heat as effectively, which causes the evaporator coil to freeze and renders your unit inoperable until the coil defrosts.
Air conditioners are not designed to operate in or produce temperatures below 60 degrees. Truth be told, they're happiest around the 68 degree mark. Most thermostats simply won't allow you to choose a setting below this mark.
Unlike low temp refrigeration systems, like your freezer, your AC unit is not designed to take your space into freezing temperatures – not even close! An AC unit is happiest creating space temperatures no lower than 68 degrees fahrenheit.
But you shouldn't run your AC if the temperature is below 60°F. Heat pumps: Modern heat pumps are effective at around 25 to 30°F. Ductless mini-splits: Avoid using the cooling function when temperatures fall below 60°F.
When the AC temperature is too low, between 60-67 degrees F (15-19 degrees C), the evaporator coil inside the unit can get excessively cold. If the humidity in the room is high, condensation can accumulate on the coil, which may lead to the formation of frost or ice.
For many of us, 70 degrees is the ideal indoor temperature, but when it is close to 100 degrees outside, your AC unit will be working quite hard to meet these expectations. Consider setting your thermostat at 75 degrees to 80 degrees in your home if the outside temperature is approaching triple digits.
What Temperature is Too Cold for a House AC? Most experts maintain that running your AC below 70 degrees can cause issues with your unit, including the risk of freezing the evaporator coil. It's worth noting this low setting would also quickly run up your energy bill.
U.S. Department of Energy research suggests that setting your programmable thermostat to 78 during the summer months is the best way to save money on your cooling costs while maintaining a comfortable temperature.
Recommended AC Temperature for Sleeping
The Sleep Foundation says 65° is the best temperature for sleeping. However, if you prefer a slightly warmer or cooler room, that's okay, too. The recommended range is 60–68°, so there is some wiggle room.
The lowest outside temperature at which to run your AC is typically around 60-65 degrees Fahrenheit. At temperatures below this range, your air conditioner might not operate efficiently, causing increased energy consumption and potential strain on the system.
Quick answer: The ideal house temperature is room temperature, which ranges from 68 to 78 degrees F, though this may vary from season to season.
What is the Best Thermostat Setting for Summer Air Conditioner Use? Energy Star recommends the following thermostat temperatures for your air conditioner in the summer: 78°F during the day if people are home. 82°F at night if people are home.
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.
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.
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.
Cooling a house from 80 to 72 degrees is a common goal for many, especially during the peak of summer. On average, this process takes roughly two and a half to three and a half hours.
For example, HVAC specialists recommend setting your thermostat no lower than 20 degrees the outside temperature. Suppose the outdoor temperature in your area is a blistering 90 degrees Fahrenheit. It's probably best to keep your thermostat between 70 and 80 degrees Fahrenheit to prevent stress on your unit.
Don't lower the thermostat below 72°F
One of the major pieces of advice you'll hear about thermostat settings is not to lower the thermostat below 68°F when cooling a house, no matter the heat hourside.
In most cases, air conditioners only have one speed (though some have variable speed settings to improve energy efficiency). Lowering the temperature too much causes your air conditioner to operate longer, causing more wear and tear on it as well as higher utility bills.
The Dangers of “Too Cold”
Additionally, lower settings can cause your evaporator coil to freeze. There isn't enough heat exchange, so ice forms on the coil, causing the system to stop working until it defrosts. Any temperature below about 68 degrees puts you in danger of freezing.
So, how cold can my air con go? Most air conditioning units are designed to go as low as 17°C, but do note that air conditioners are designed to achieve an inside temperature that is up to 11°C lower than the outside temperature.