It’s hot – there’s really no other way to say it.

Alabama is in the middle of a scorching summer heatwave and many are retreating indoors in search of cool air. That means air conditioners are running full blast, causing strains on units and forcing higher utility bills.

But there is something you need to keep in mind when setting your thermostat to cool your house. It’s called the 20-degree rule and, according to Huntsville Utilities, it plays a big role in how your house feels and how much your utility bill will be.

According to HU, you should never set your thermostat for a temperature more than 20 degrees cooler than the outside air. Most air conditioning systems can only handle a 20-degree difference between the outside and inside air temperatures, so if it’s a relatively mild 80 degrees outside, your unit will have no problem keeping the indoor temperature at 70 degrees. But if it’s over 90 degrees – or as in Alabama this week and approaching 100 degrees- your unit will have to run non stop to get indoor temperature to 70 and even then it still might not make it.

Constantly running your air conditioning unit will cause utility bills to skyrocket.

Instead, experts recommend setting your thermostat to 78 degrees.

There are things you can do to help keep your home cool without breaking the bank – or your air conditioning unit.

READ MORE: Which way should your ceiling fan blades turn to help cool your room?

Here’s what they recommend:

Let the light in – Leave your lights off in the mornings and evenings and open your blinds. Using natural light to illuminate your home helps reduce energy consumption just remember to close your blinds during the hottest part of the day or before you leave for work.

Keep the heat out – – Invest in thermal curtains that keep out heat and light. The most effective are those with blackout technology with at least two layers of woven fabric. Close your curtains during the hottest part of the day – noon – 4:30 p.m. – to keep the heat out.

Set it and forget it – This one might be the most controversial tip. Alabama Power recommends setting your thermostat at 78 degrees during the day and turning on your ceiling fans to stay cool. If you prefer to set your thermostat at a lower temperature, follow the 20-degree rule. For example, if it’s 94 degrees outside, set your temperature to 74 degrees. Setting the thermostat below the 20 degree benchmark can stress your unit and, ultimately, shorten its life.

Use your exhaust fan – After removing food from the oven or after cooking on the stove top, turn on the exhaust fan to remove hot air from the room. Turn it off after 15 minutes to make sure it doesn’t start removing air conditioned air. Check to make sure the grease filter is clean in the range hood so that it vents properly.

Keep the cool air coming – Your AC unit must work harder when the air filter is dirty or the vents are clogged with dust. Clean the vents, open them completely and change the air filter to make the AC unit work more efficiently.

Air it out – Small appliances – think air fryer or Instant Pot or indoor grill – cook faster, use less energy and produce less heat.

Consider the time of day – Use large appliances such as the washer and dishwasher, during the coolest parts of the day, such as the mornings or evenings.