How cold should your AC actually be able to make your house?
Air conditioning doesn’t cool to a set temperature so much as it removes a certain amount of heat per hour. As a rule of thumb, central air conditioning can cool a home to about 20 degrees below the outdoor temperature. That gap between indoor and outdoor air is what HVAC technicians call the temperature differential.
What that looks like in practice during an NYC summer: when it’s 90 degrees out, a properly working system should comfortably hold the low 70s indoors. When it climbs to 98, holding 76 to 78 is a realistic target — not a sign of failure. The hotter it gets outside, the harder your system works just to maintain that same 20-degree spread, which is exactly why a unit that felt more than adequate in June can suddenly seem to “give up” during the first real heat wave. Nothing changed inside the equipment; the demand on it jumped.
This is also why setting your thermostat to 65 on a 97-degree day doesn’t help. The system can’t reach 65 when it’s that hot out, and asking it to try just means it runs continuously, works harder, and in some cases freezes up. A realistic target during extreme heat keeps the system running efficiently and keeps your home as cool as it can reasonably get.
Is your AC just maxed out, or actually broken?
The useful question during a heat wave isn’t “why isn’t it cold?” — it’s “is the gap between inside and outside holding?” If your system is maintaining roughly 18 to 20 degrees below the outdoor temperature, it’s working as designed, even if 78 indoors doesn’t feel as cool as you’d like. If that gap is shrinking — if the distance between indoor and outdoor temperature keeps closing over the course of the day — that points to a real problem.
Here’s the quick way to tell the two apart:
- Probably normal in extreme heat: the system runs almost constantly, holds about 20 degrees below the outdoor temperature but no colder, struggles most in the late afternoon when the sun and outdoor heat peak, and recovers overnight as the city cools down.
- Signs of a real fault: the indoor-to-outdoor gap keeps shrinking (you’re only getting 8 to 10 degrees of cooling), the vents blow warm or room-temperature air, there’s ice on the refrigerant line or indoor coil, water is pooling near the indoor unit, the breaker keeps tripping, or the system short-cycles or won’t restart.
If your symptoms fall in the second group, that’s no longer the heat overwhelming a healthy system — it’s a fault in the equipment itself, and it’s worth a dedicated diagnostic rather than waiting for the weather to break. A frozen coil, a clogged condensate drain, low refrigerant from a leak, or a failed electrical part each produce that pattern, and none of them fix themselves.
Why NYC homes feel the heat more
Two homes can run identical equipment and have very different experiences in a heat wave, and in NYC the reasons are usually structural. A lot of the city’s housing stock — brownstones, prewar co-ops, small multifamily buildings — has limited insulation, original windows, and ductwork that was retrofitted into a building never designed for central air. All of that lets heat in faster than the system can pull it out, so the same 98-degree day that barely fazes a newer, well-sealed home leaves an older one fighting to hold 78.
Electrical capacity plays a role too. Many older NYC homes and apartments can’t support a larger or additional cooling system without a panel upgrade, which is why some homes are running equipment that’s simply undersized for the space. And the outdoor side of the system matters more here than almost anywhere else. Condensers tucked into tight rear yards, side alleys, or dark rooftops run hotter than units sitting in open suburban yards, and a condenser that can’t shed heat efficiently loses capacity at exactly the moment you need it most. During citywide demand spikes, voltage sags and brownouts can stress compressors further. None of these are reasons to panic — they’re reasons a heat wave exposes weaknesses that stay hidden the rest of the year.
What you can do right now to help your AC keep up
Before you assume something’s wrong, a few things genuinely help during extreme heat. Close blinds and shades on sun-facing windows, especially in the afternoon, and hold off on heat-generating activities like running the oven during peak hours — every bit of heat you keep out is heat the system doesn’t have to remove. Check your air filter, because a clogged one is the single most common reason a healthy system loses airflow and stops keeping up; replacing it is the easiest fix that actually restores performance. Make sure the outdoor condenser is clear of leaves, bags, and debris and has room to breathe.
Most importantly, set a realistic target. Aiming for 76 to 78 on a 98-degree day lets the system cycle and stay efficient. Cranking the thermostat way down doesn’t cool your home any faster — it just runs the system continuously and raises the risk of the coil icing over, which leaves you worse off than when you started.
When it’s time to call for service
If your AC stops cooling entirely, blows warm air, won’t restart, or you see ice on the lines during a heat wave, that’s the moment to call rather than wait it out. Energo’s emergency service is available every day of the year, including weekends and holidays, and our fully trained, NORA-certified technicians can diagnose why a system has stopped keeping up. You can read more on our emergency HVAC services page about how that works.
There’s also a longer-term decision underneath a lot of “can’t keep up” calls. If a system consistently can’t hold a reasonable temperature, is 12 to 15 years old or older, or needs major refrigerant or compressor work, repair may be throwing money at a unit that’s near the end of its life. ENERGY STAR suggests considering replacement once a system is more than 10 years old and needing frequent repairs. Replacing it with a properly sized, energy-efficient system often makes more sense than another fix — and right-sizing matters, since an undersized system will never keep up no matter how new it is. The most reliable way to avoid being caught out, though, is prevention: a pre-season tune-up keeps capacity up and catches small problems before a heat wave turns them into an emergency. If you haven’t had yours looked at, our guide on whether you should service your AC before summer in NYC walks through what that visit covers, and window AC vs. central cooling for NYC homeowners can help if you’re weighing a system change.
What this means for property managers and commercial buildings
In larger buildings, “the AC can’t keep up” usually points somewhere different than it does in a house. It’s more often a zoning problem, an overloaded rooftop unit, or a controls issue than a single failed part — which means the fix starts with figuring out which zones or units are falling behind, not swapping a component. Heat-wave load and tenant comfort raise the stakes, so the buildings that ride out extreme heat best are the ones that handle pre-season checks early and have a responsive service partner lined up before July. For more on that, see what to check in a commercial HVAC system before cooling season and commercial HVAC repair vs. replacement in NYC.
Frequently asked questions
How many degrees below the outside temperature can my AC actually cool?
As a general rule, a healthy central air system or mini-split can cool a home to about 15 to 20 degrees below the outdoor temperature. On a 95-degree day, holding the mid-to-high 70s indoors is normal, not a sign the system is failing.
Is it bad to run my AC nonstop during a heat wave?
No. In extreme heat, a properly sized system running almost continuously is expected and is generally more efficient than short, frequent cycles. Constant running only becomes a concern if it’s paired with warm air, ice on the lines, or a shrinking gap between indoor and outdoor temperature.
Why won’t my AC go below 75 even though it’s set to 68?
Because air conditioning can only cool so far below the outdoor temperature. If it’s 95 out, the system may physically be unable to reach 68 no matter where you set the thermostat. Setting it lower won’t speed anything up — it just keeps the system running and can cause the coil to freeze.
When should I call for emergency AC repair?
Call when the system blows warm air, stops cooling entirely, won’t restart, keeps tripping the breaker, or has ice on the refrigerant line during a heat wave. Energo’s emergency service is available every day of the year, including weekends and holidays.
Should I repair or replace an AC that can’t keep up?
It depends on age and cost. A system that’s 12 to 15 years old or older, needs major refrigerant or compressor work, or repeatedly fails to hold a reasonable temperature is often better replaced with a properly sized, efficient unit than repaired again.
Does Energo service my area?
Energo serves homeowners and buildings across the NYC boroughs — Brooklyn, Queens, Manhattan, the Bronx, and Staten Island — as well as Westchester and Nassau.
Schedule service before the next heat wave
If your AC has stopped keeping up and the checks above point to a real fault, don’t wait for the city to cool down on its own. Reach out through our contact page or call to schedule a diagnostic — our team is available every day of the year, including weekends and holidays.
Why Your AC Can’t Keep Up in a Heat Wave (And When It’s Actually Broken)
When it’s 95 degrees outside and your AC is running nonstop but the house still won’t drop below the mid-70s, the system usually isn’t broken — it’s doing roughly what it was built to do. Most central air conditioners and mini-splits are designed to cool a home to about 20 degrees below the outdoor temperature, not to a fixed number on the thermostat.
Why Won’t My Standby Generator Start? NYC Homeowner’s Guide
The most common reason a standby generator won’t start is a weak or dead battery. After that, the usual culprits are a fuel-supply problem, a low-oil shutdown, the controller being left in “Off” instead of “Auto,” or an overcrank lockout after the unit tried and failed to start. A few of these are safe to check yourself. The rest — battery, oil, fuel, and electrical work — belong with a technician.