MEMPHIS, Tennessee — With scorching temperatures outside and a Heat Advisory in effect for much of the Mid-South, you want to stay as cool as possible when you get home.
One viewer asked ABC24 News about the "20-degree rule"—is it true? Also should you take the heat index or actual temperature into account when adjusting your A/C?
Question:
Is the "20-degree rule" accurate? Should you still keep your A/C unit 20 degrees lower with a high heat index?
Answer:
Yes
Our source:
Sam Mullins, the owner of Automatic Air Conditioning, Heating & Plumbing
What we found:
Mullins said, typically the public knows the 20-degree rule to mean you should keep you’re A/C no more than 20 degrees lower than the outside temperature.
“In the air conditioning business we talk about 20 degrees because it’s a 20-degree drop across the evaporator coil.”
Mullins further explains, "if it’s 95 degrees outside, that’s not what your indoor temperature is. You might be at 75 degrees, so we can drop the temperature down to about 55.”
The "20-degree rule" is true but is not a hard and fast rule. Rather, it is a rule of thumb.
Still, should you judge by the heat index or actual temperature? Mullins said if you’re looking for comfort, take the heat index into account.
If 72 degrees keeps you feeling fresh and cool inside, keep it at that.
"When it gets really hot outside, if you have poor insulation, if you have really poor windows—you’re going to be adding heat to the space faster than you can take it out,” Mullins said.
So yes – ABC24 can verify you should look at the heat index when adjusting you’re A/C unit.
Mullins is cautioning people not to turn the A/C unit off when you’re out of the house, but turn it up a few notches to 75 degrees if the utility bill is a concern.
It’s important to note that your ductwork and attic insulation are critical, helping maintain your indoor temperature. To help more, close blinds and keep window curtains pulled on eastern and western facing walls.
“That way sunlight isn’t adding heat back to the space faster than you can take it out,” Mullins said.
Also, keep your A/C unit and air filter clean. Mullins’ company is getting 70-80 calls a day. Half of them he said are due to owners not doing proper maintenance.
If you see something that you want our team to look into, e-mail us at verify@ abc24.com, or you can hit us up on social media at ABC24 Memphis.
