The 20-Degree AC Myth Oklahoma Renters Keep Hearing

There’s a very specific kind of Oklahoma summer misery happening right now.

You walk into your house, turn the thermostat down, and wait.

And wait... And wait...

Eventually you realize the air conditioner has been running non-stop, but it's not getting any cooler. It’s 105 degrees outside, it's bound to happen.

This has led to a whole lot of air conditioning complaints on social media lately. Some are from homeowners dealing with a busted unit, which is bad enough. But in a military town like Lawton, there’s another group asking a slightly different question.

“Is my landlord telling me the truth?”

Like most renters, you’ve probably heard this explanation...

An air conditioner can only cool your house about 20 degrees below the temperature outside. So if it’s 105 outside, 85 degrees inside is just what you should expect.

Is that true? No. No, it's not... Well, sort of.

This is where a decades-old piece of air conditioning wisdom has gotten twisted around.

The 20-degree number is actually a pretty useful measurement. It just isn’t measuring what you and every landlord in America thinks it is.

It’s the temperature difference between the air going into your air conditioner and the air coming back out.

If your house is 75 degrees and the system is working properly, you might expect the air coming out of the vents to be anywhere from 50 to 55 degrees. That’s the common industry standard temperature split, and the anecdotal measurement everybody keeps talking about.

It's also not the end all/be all of HVAC, just a general rule of thumb... Well, for houses and apartments. Vehicle HVAC is totally different, and there's plenty of complaining on Facebook about that too.

Here's a quick sidequest rundown... Your car's system is designed to cool a much smaller space, and the temperature difference coming out of the vents can be huge. 105 degrees outside, and 40 degrees blowing out of your dashboard. If yours isn't that cold, you might have it looked at.

While I normally encourage people to try doing their own maintenance, repairing your own vehicle's air conditioning isn't one you should gamble with. The DIY kits at the store make it seem easy, but it's really easy to do a lot more harm than good with those. When my AC finally gave out, I tried to fix it for a month... And Redd's Automotive up on North Sheridan had it blasting 40-degree air again in just a couple of hours.

So many sweaty drives home for work for something so easy for them to fix.

Back to your house, it's a different story.

How To Tell If Your AC Is Working Properly

This is also something you can actually check yourself. Go grab a thermometer.

Measure the temperature of the air going into the return vent, then measure the air coming out of a supply vent. You’re looking for roughly that 15-to-20-ish degree difference under normal conditions.

If you’re getting that much of a temperature difference, your AC is doing pretty well, which can still be irritating to discover if you're still having issues. If your AC is blowing cold air, but your house is still getting hotter and hotter during the afternoon, it's probably a house problem.

Your air conditioner has to fight the amount of heat your home is absorbing. The hotter the attic, walls, windows, and other parts of the building get, the harder that little mechanical box has to work to keep the living space comfortable.

And that comes down to something called thermal load.

In normal-person language, your house needs to be able to keep the heat outside.

Why Your House Gets Hot Even When The AC Works

This is why insulation is such a big deal.

I learned that one myself.

My house was built in the 1980s, and when I first moved in, I went into the attic and discovered there was barely three inches of insulation up there.

Three inches... But I guess that was probably the code back in the 80s when it was built, and every homeowner before me just accepted turning the AC on in March. So one of my first homeowner investments was attic insulation.

I had blown-in fiberglass added until there was roughly 14 to 16 inches up there, depending on where you measure.

It got thicc, and the difference was immediate.

The house stayed cooler. The air conditioner didn't need to come on until late April or early May. And my average-pay electric bill is still under $100 a month... Of course, I'm still pretty sore that I'm still using the same amount of energy on average as I did when I moved in in 2017, but I was only paying $60/month until everything skyrocketed with the previous administration.

All the same, I try to stay thankful that during this stretch of 105-plus-degree Oklahoma heat, my air conditioner isn't running constantly.

That’s because the AC isn't the only thing keeping the house cool. The house plays a large part in it too. So if you're renting and your air conditioner seems to run forever but never quite catches up, there are a couple of things worth checking before you assume the AC is broken.

Check That Temperature Difference

If the air coming out of your vents is roughly 15 to 20 degrees colder than the air going into the system, that's a pretty good sign the unit is doing its job.

Then look at the house.

If you've got an attic you can safely access, take a peek. You don't need to be an HVAC tech to notice when there's barely any insulation up there. If the AC is working properly but the building is getting hotter during the day, that's a different problem.

And no, your landlord may not be intentionally lying to you, only accidentally.

That 20-degree thing has been repeated for so long, most people don't realize they've got it backwards. Somewhere over the last couple of decades, the whole “your AC should have about a 20-degree temperature split” became “your AC can only make your house 20 degrees cooler than outside.”

Those are two very different things.

The next time somebody tells you that 85 degrees inside a house is perfectly normal because it's 105 outside, grab a thermometer and science it before you start getting stabby... Your air conditioner might actually be working fine.

And if it is, you may have a much bigger question to ask your landlord about... Something to the tune of updates or having cause to break a lease.