Cielo
Ever wondered how low you should set your AC when outside temperatures start climbing? The 20-degree rule offers a simple answer: keep your thermostat no more than 20°F below the outdoor temperature. But is this rule the sweet spot for staying cool, or can it help keep your energy bills in check?
Let’s find out!
- What Is the 20-Degree Air Conditioning Rule?
- Is the 20-Degree Rule an Actual Guideline or Just a Myth?
- How Can the 20-Degree Rule Help Lower Your Energy Bills?
- Does the 20-Degree Rule Prevent HVAC Strain?
- Does the 20-Degree Rule Work in Extreme Weather?
- How to Reduce AC Costs Without Sacrificing Your Comfort
- The Bottom Line
Key Takeaways
- The 20-degree AC rule recommends setting your thermostat no more than 20°F below the outdoor temperature.
- This rule helps your AC cool efficiently without driving up bills.
- Setting your thermostat too low can strain your HVAC system over time.
What Is the 20-Degree Air Conditioning Rule?
The 20-degree air conditioning rule is a simple rule of thumb for choosing a reasonable thermostat setting during hot weather. It suggests keeping your indoor temperature within 20°F of the outdoor temperature.
For example, if it’s 90°F outside, the rule suggests setting your thermostat to around 70°F or higher.
Budget-friendly smart thermostat for central HVAC systems. A thermostat that guarantees savings.
Award-winning smart thermostat for mini-splits. Technology that goes above & beyond.
Sleekest smart thermostat for mini-split, window & portable ACs. A design that magically blends.
Smart mini-split thermostat that is engineered for affordable comfort. Small in size, big in benefits.
Is the 20-Degree Rule an Actual Guideline or Just a Myth?
The 20-degree rule is better understood as a general guideline than an official recommendation.
It discourages excessively low thermostat settings that can drive up bills. The greater the temperature difference between indoor and outdoor temperatures, the greater the cooling load your AC has to handle.
Setting your thermostat significantly lower does not make your air conditioner cool your home proportionally faster. Instead, it gives the system a lower temperature target to reach and maintain.
For example, if it is 100°F outside:
- A 78°F thermostat setting creates a 22°F difference.
- A 68°F thermostat setting creates a 32°F difference.
The lower setting requires the AC to remove more heat from the home, which can increase runtime and energy consumption.
How Can the 20-Degree Rule Help Lower Your Energy Bills?
The primary benefit of the 20-degree rule is that it helps avoid unnecessarily low thermostat settings that can increase cooling demand.
-
A Higher Setpoint Can Reduce Cooling Demand
The lower you set your thermostat during hot weather, the more cooling your home requires.
For example, if your home is comfortable at 76°F, lowering the thermostat to 68°F simply because outdoor temperatures are high creates additional cooling demand.
ENERGY STAR recommends keeping the thermostat as high as comfortably possible during summer, with 78°F commonly cited as a starting point when you are home.
-
Lower Runtime Can Reduce Energy Consumption
A lower thermostat setting generally requires the system to remove more heat to reach and maintain the desired temperature.
This matters most during prolonged periods of extreme heat, when the AC is already handling a high cooling load. Choosing a reasonable thermostat setting can help limit unnecessary runtime and keep cooling costs under control.
Does the 20-Degree Rule Prevent HVAC Strain?
The 20-degree rule can help limit unnecessary strain on your AC. The greater the difference between the outdoor temperature and your indoor setpoint, the more heat your system must remove and the longer it must run to maintain the desired temperature.
Setting the thermostat significantly lower than necessary can therefore increase AC runtime, particularly during periods of extreme heat. Over time, extended runtime can increase energy use and add wear on the compressor and other system components.
Does the 20-Degree Rule Work in Extreme Weather?
Consider a 105°F day. Following the rule would mean setting your thermostat to around 85°F. While this may reduce cooling demand, it may not provide the comfort level you want, particularly in hot and humid conditions.
You do not need to follow the 20-degree difference exactly during extreme weather. Instead, choose a thermostat setting that provides reasonable comfort without unnecessarily lowering the temperature.
During extreme weather, combine a reasonable thermostat setting with other measures such as shading windows, using ceiling fans, maintaining good airflow, and keeping your HVAC system properly maintained.
How to Reduce AC Costs Without Sacrificing Your Comfort
Following the 20-degree rule is only one way to manage cooling costs. These additional strategies can help reduce AC runtime while keeping your home comfortable.
Keep the Heat Out
Close blinds or curtains during the hottest part of the day, particularly on windows exposed to direct sunlight. Proper insulation and sealing gaps in doors and windows can also reduce heat transfer into your home.
Use Ceiling Fans
Ceiling fans can improve comfort without lowering the thermostat. They create a cooling breeze that helps you feel cooler while allowing you to keep the AC setting slightly higher.
Keep Your Filter Clean
A dirty or clogged filter can restrict airflow and reduce system efficiency. Check your filter regularly and clean or replace it according to the manufacturer’s recommendations.
Use a Smart Thermostat
A smart thermostat can automate temperature adjustments based on your schedule, occupancy, and preferences.
Instead of manually changing the thermostat whenever you leave, return home, or go to bed, a smart thermostat can automatically adjust the temperature to avoid unnecessary cooling when the home is unoccupied.
ENERGY STAR-certified smart thermostats are also designed to help reduce heating and cooling energy use through features such as scheduling and location-based controls. They can save about 8% on heating and cooling bills annually.
Equip your HVAC system with smart features and achieve the perfect balance between comfort & savings.
Learn more
The Bottom Line
The 20-degree rule is a useful guideline to keep in mind. It helps homeowners avoid setting their thermostat unnecessarily low, since that only increases cooling demand, runtime, and energy use.
During extreme heat, aim for a comfortable setting. Pair that with regular HVAC maintenance, proper airflow, and smart thermostat control to stay comfortable without costly bills.
