Why Your House Is Too Hot During a Heat Wave (And What to Actually Do About It)

If your house has been too hot during this heat wave and you’re convinced your AC is dying, hold off before you call anyone in a panic. It might be, sure. But there’s a decent chance your system is actually doing exactly what it’s supposed to do and just getting absolutely overwhelmed by conditions it was never designed to handle.

We’ve been out on a lot of calls this week. When it’s 100 degrees outside with a heat index pushing 110, that changes the math on what your air conditioner can realistically accomplish. Here’s what’s going on and what you can actually do about it.

Your AC Was Not Designed for This

Most residential HVAC systems are sized to maintain about a 20-degree difference between the outdoor temperature and your indoor set point. So if it’s 95 outside, a properly sized system should be able to hold 75 inside without too much trouble. When it’s 102 degrees with brutal humidity on top of that, you’re asking the system to do more than it was ever engineered for.

That doesn’t mean it’s broken. It means it’s running constantly and still losing ground, which is genuinely different from a mechanical failure. The first thing to figure out is whether you’re dealing with an overwhelmed system or an actual problem. A system that’s running nonstop but still putting out cold air at the vents is probably just working as hard as it can. A system that’s running nonstop and blowing warm or barely cool air is a different story and worth a call.

What to Do When the House Is Too Hot in a Heat Wave

The goal during extreme heat isn’t to win, it’s to reduce how hard your system has to work so it can at least keep the house livable. A few things that actually help:

Keep blinds and curtains closed on any windows that get direct sun during the day. This sounds basic but it makes a real difference. South and west-facing windows in the afternoon are especially brutal, and a lot of the heat load your AC is fighting is coming straight through the glass.

Set your thermostat and leave it alone. Dropping the set point when it’s this hot doesn’t make the system cool faster, it just makes it run longer. Pick a temperature you can live with, something in the 76 to 78 range if your system is struggling, and let it work. Constantly adjusting it up and down doesn’t help anyone. Once the ambient outdoor temperature drops to a reasonable level when the sun is down and your system isn’t constantly running, you can set the thermostat lower (keeping in mind the ~20-degree rule). This can help it stay cooler a bit longer in the morning as well.

Run ceiling fans in rooms you’re occupying. Fans don’t cool the air but they make you feel cooler by helping to evaporate moisture from your skin, which means you can tolerate a higher thermostat setting without being miserable. Make sure that the blades are angled up in the direction that the fan is turning so that it pushes air downward. Another added benefit is that fans cause turbulence as they circulate the air, which helps distribute the cool air rather than leaving it lying low to the ground. Just remember to turn them off when you leave the room since they only help if someone’s in there to feel them.

Avoid running heat-generating appliances during the hottest part of the day. Ovens, dryers, dishwashers—all of these dump heat into the house at exactly the wrong time. Push laundry and cooking to the morning or evening if you can.

Check your air filter. A clogged filter during a heat wave is a problem. It restricts airflow across the evaporator coil, which reduces the system’s ability to move heat out of the house at the exact moment you need it working at full capacity. If you haven’t changed it in a while, change it now.

Signs Something Is Actually Wrong

Like we said, a system running constantly in extreme heat isn’t automatically broken. But there are a few things that do indicate a real mechanical issue worth looking at.

If the air coming out of your vents isn’t cold (not just “not as cold as I’d like” but genuinely warm or room temperature) that points toward a refrigerant issue or a failing compressor. If you see ice forming on the refrigerant lines or the indoor unit, that’s also a sign something’s off, usually low refrigerant or an airflow problem. And if the system is short cycling, meaning it kicks on for a few minutes and then shuts off repeatedly without completing a full run, that’s worth a call too.

The short version: if it’s blowing cold and running constantly, give it time and reduce your load. If it’s not blowing cold, call someone.

If You’ve Been Thinking About an Upgrade

Heat waves have a way of making people finally pull the trigger on a replacement they’ve been putting off. If your system is more than 12 to 15 years old and is really struggling this week, it’s not going to get better. Older systems lose efficiency every year, and extreme heat exposes that faster than anything.

If that’s where you’re at, we’re happy to come take a look and give you a straight answer on whether repair or replacement makes more sense. Check out our AC and cooling services for more on what that process looks like, or get in touch here to schedule something.

Frequently Asked Questions

Why can’t my AC keep up when it’s over 100 degrees?

Most residential systems are designed to maintain roughly a 20-degree difference between outdoor and indoor temperatures. When it’s 100 or above, especially with high humidity on top of that, you’re pushing past what the system was sized for. Running constantly and still losing a few degrees is normal in extreme heat. It doesn’t necessarily mean something is wrong.

Should I turn my AC off during a heat wave to give it a rest?

No. Turning it off lets the house heat up significantly, and then the system has to work even harder to bring the temperature back down when you turn it back on. Better to keep it running at a slightly higher set point than to cycle it off and on.

How do I know if my AC is broken or just overwhelmed by the heat?

Check what’s coming out of the vents. If it’s cold air and the system is just running constantly, it’s probably overwhelmed rather than broken. If the air is warm or barely cool, if you see ice on the unit or lines, or if the system keeps shutting off after only a few minutes of running, those are signs of an actual mechanical issue worth having someone look at.

What temperature should I set my thermostat to during a heat wave?

Something in the 76 to 78 range is realistic when it’s extremely hot outside. Trying to hold 70 or 72 during a heat wave puts enormous strain on the system and may not even be achievable. Ceiling fans, closed blinds, and avoiding heat-generating appliances during peak afternoon hours will make a higher set point feel much more comfortable.