During a heat advisory, keep your AC running steadily at 75–78°F — don’t crank it lower, which only overworks it. Ease its load: close blinds, run ceiling fans, skip the oven, change the filter. Expect indoor temps about 15–20°F below outside. If vents blow warm or ice forms, call for service and get somewhere cool.
That’s the answer, up front, because on a day like that nobody should have to scroll for it. What follows is the longer truth, which is mostly about expectations — yours, and your air conditioner’s.
What counts as a heat advisory here?
Every place has its own threshold for alarm, which is a polite way of saying every place has its own tolerance for suffering. In parts of New England, the National Weather Service starts issuing advisories when the heat index touches 95. Here — Orlando sits in the NWS Melbourne zone — the bar is 108. One hundred and eight. It takes a heat index of 113 before the language escalates to Extreme Heat Warning. We have, officially and meteorologically, one of the highest pain thresholds in America, and the weather service knows it, and it calibrates accordingly.
So when an advisory actually lands — and most summers Central Florida only gets one or two, bunched into July and August, though 2023 threw twenty-five of them at us — understand that it isn’t the government being dramatic about a warm afternoon. It’s the day your air conditioner works harder than it will work all year. It is the machine’s marathon, and it did not train for this. It was never supposed to.
What should I set my thermostat to during a heat advisory?
Seventy-five to seventy-eight while you’re home. Eighty or a bit above while you’re out or asleep. That’s it. That’s the setting.
The instinct, of course, is to do the opposite. The house feels warm, so you march to the thermostat and drop it to 68, the way you’d turn up a radio that’s too quiet. But a thermostat is not a volume knob. The Department of Energy says it flatly: a lower setting will not cool your home any faster. The system has one speed, and it’s already running at it. All 68 accomplishes is the removal of any finish line — the machine runs flat out for hours with no off-cycle, no rest for the compressor, no moment for the refrigerant to settle. This is precisely how July eats compressors and capacitors. It also makes the house clammy, because a system pushed past its limits stops pulling moisture from the air, and in Florida the moisture is half the fight.
Steady and modest outlasts low and desperate. In air conditioning as elsewhere.
Why won’t my AC cool the house below 80 when it’s 100 outside?
Because it was built with a ceiling, and this is the useful, faintly humbling fact at the center of everything: a residential air conditioner is engineered to hold a house roughly 15 to 20 degrees below whatever it is outside. Not to a number you pick. Below the world by a fixed margin. People in the trade call it the 20-degree rule.
Run the arithmetic and the “broken” AC starts to look innocent. Ninety-five outside, 76 inside: working. A hundred outside, 80 inside: working, at the very edge of what its designers asked of it. Struggling at four in the afternoon and catching up after sundown: normal, even a little valiant.
The reason it works this way is unglamorous. Systems are sized for a region’s ordinary hot day — high 80s, low 90s here — not its record. A unit big enough to laugh at 108 would be miserable the other 360 days, cycling on and off too fast to dry the air. So the engineering makes a bet on the typical, and advisory days are when the bet gets called.
(This is a rule of thumb, not a law of physics — insulation, ductwork, and the age of the machine all move the number. If your gap is much worse than 20 degrees, keep reading.)
How do you help an air conditioner through a day like this?
You take things off its plate. In roughly the order that matters:
The filter first. A clogged filter starves the system of air, and a starved coil gets so cold it freezes — a fine irony, ice being how ACs die in a heat wave. It’s a two-minute fix and the single most common cause of the calls we run in July.
Then the sun. Blinds and curtains closed on the south and west sides during the afternoon. Sunlight through glass is a space heater you didn’t ask for.
Ceiling fans, counterclockwise — with the understanding that fans cool people, not rooms. The breeze buys you about four degrees of perceived comfort, which lets you leave the thermostat a little higher. An empty room with a spinning fan is just spending electricity.
The oven stays off until dark. So, ideally, do the dryer and the dishwasher. A stovetop dinner can lift a kitchen ten degrees, and every one of those degrees gets handed to the AC as overtime.
Outside, give the condenser some air. Two feet of clearance, a gentle rinse to get the pollen and grass clippings off the coil. That box’s whole job is throwing heat out of your house; buried in debris, it can’t.
And if you feel like getting paid for your trouble: Duke Energy’s EnergyWise Home and FPL’s On Call programs will credit your bill — Duke says up to $141 a year, FPL up to $137 — for letting them briefly cycle your equipment during peak demand, which they rarely do. The amounts drift year to year; check the current pages.
Is it failing, or just struggling?
The distinction that matters most, and the one worth a table:
| Probably just the heat | Probably a real problem — call |
|---|---|
| Runs nearly nonstop | The indoor-outdoor gap keeps shrinking — you’re only getting 8–10 degrees |
| Holds 15–20°F below outside, but no colder | Warm air from the vents |
| Suffers most in late afternoon | Ice on the refrigerant line or coil |
| Recovers overnight | Water pooling at the indoor unit, a breaker that keeps tripping, short bursts of on-off, a burning smell, or silence |
The left column is a machine at its limit. The right column is a machine with an injury, and heat waves do not heal injuries — they finish them. A weak capacitor on Tuesday is a dead compressor by Friday if it never gets to rest. If you’re in that right column, our Orlando AC repair team answers around the clock, and we don’t charge extra for nights or weekends, because breakdowns have never once consulted a business calendar.
When does a broken AC stop being an inconvenience?
When the indoor thermometer crosses into the 90s, roughly — and faster than that for the people heat goes after first: anyone over 65, infants, the chronically ill, and pets, who cannot tell you they’re in trouble. Most heat-stroke deaths in this country happen indoors, in homes where the air conditioning wasn’t working. A Florida house without AC in August isn’t uncomfortable. It’s unsafe.
So while you wait for the repair: the coolest room in the house, lowest floor, sun side avoided. Water steadily, before thirst, and skip the beer and the sweet tea — alcohol and sugar work against you. Cool showers, as many as you like. And know a fan’s limits: once the heat index is pushing 100, a fan is moving hot air across your skin and calling it comfort. It isn’t lowering your temperature.
If the house turns dangerous, leave it. Orange County opens cooling centers — libraries, rec centers, community spaces — when the heat index hits 103, and LYNX runs free rides to them. (Thresholds and locations get updated each season; confirm the county’s current page.) A mall works. A library works beautifully.
And the medical bright line, worth memorizing: heavy sweat, dizziness, nausea — that’s heat exhaustion; cool off and drink. Confusion, slurred words, skin hot to the touch — that’s heat stroke, and that’s 911, immediately.
Why is Florida harder on air conditioners than everywhere else?
Two reasons, and they explain why advice written for Phoenix or New Jersey undersells your situation.
The first is water. Orlando’s summer air carries dew points around 73 and humidity that averages 74 percent, and before your AC can make the air cooler it has to make the air drier — a second, invisible job that dry climates never assign. It’s also why the thermometer can read 93 while your body files a complaint about 108.
The second is the calendar. An air conditioner up north works maybe a thousand hours a year. Yours works three or four thousand. Same machine, triple the mileage — which is why systems here retire at 10 to 15 years instead of the national 15 to 20, and why maintenance in Florida isn’t fussiness, it’s math. If yours is deep into its second decade and wheezing through advisories, the honest question is whether to keep paying for its convalescence — we wrote out how to decide whether a 20-year-old unit is worth fixing, with the arithmetic included.
The cheaper conversation happens before the hottest day, not on it. That’s the entire premise of our $79 WOW Tune & Clean — the coil cleaning, the capacitor and contactor checks, the refrigerant pressures, the drain line — the unglamorous work that decides which column of that table you end up in come August.
Frequently Asked Questions
Why is my AC not keeping up in extreme heat? Most likely it’s at its design limit — systems hold about 15–20°F below the outdoor temperature, so 78–80 inside on a 100-degree day is normal. If your gap is smaller than that, check the filter, then the outdoor coil. Warm air from the vents or ice on the lines means an actual fault.
Is it bad to run my AC all day during a heat advisory? No. Steady operation at 75–78 is what it’s built for. What’s bad is asking it to chase 68 with no rest, or skipping the maintenance that makes continuous running safe.
Should I turn the AC off during extreme heat to give it a rest? No. Recovering a 90-degree house is far harder on the equipment — and on you — than holding a steady temperature. Raise the setpoint a few degrees instead.
What is the 20-degree rule for AC? Residential systems are engineered to hold indoor temperatures roughly 15–20°F below outdoor temperatures. It’s a design characteristic, not a defect — and a rule of thumb that shifts with insulation, ductwork, and the machine’s health.
How do I know if my AC is undersized? If it can’t hold that 15–20 degree margin even on an ordinary 90-degree day — clean filter, clean coil — it may be undersized or losing capacity. A professional load calculation settles it.
Does a heat advisory mean I should get my AC serviced? The right time is before advisory season. But if the system is visibly struggling now, a tune-up can recover real capacity — clean coils and correct refrigerant pressure directly improve cooling output.
The phone rings most on days like this. We answer.
Our Place Air & Home Repair runs 24/7 emergency AC repair — no night fees, no weekend fees — across Orlando, Ocala, Kissimmee, The Villages, Tampa, and Hudson, from offices in Orlando and Ocala. Licensed Florida HVAC contractor CAC1819097. 4.8 stars across 2,000+ Google reviews.
1-800-291-0949. Before you replace… Call Our Place.