When the power goes out during a hurricane, running your central AC on a generator comes down to one number: starting watts, not running watts. A 3 to 5 ton system typically needs a generator rated for at least 10,000 to 17,000 starting watts to get the compressor moving, even though it only draws 3,500 to 5,000 running watts once it's up and running. Most homeowners size their generator off the running number, find out the hard way that the compressor won't start, and risk burning it out trying to force it.
- A central AC system needs 10,000 to 17,000 starting watts from a generator, not just 3,500 to 5,000 running watts.
- Portable generators without a soft start device often can’t handle an AC compressor’s surge, even at 8,000 to 12,000 watts.
- Whole-home standby generators rated 20 to 24 kW run a full South Florida house, AC included, without load management.
- A soft start device can cut an AC unit’s starting watt draw by roughly half, making a smaller generator workable.
- Ac generator power outage planning should happen before hurricane season, not during the storm watch.
Why this matters
South Florida homes lose power for days, not hours, after a named storm rolls through Palm Beach and Martin counties. A house that sits closed up at 90 degrees for 48 hours breeds mold fast, especially in older homes with block construction and small return air ducts that already struggle with humidity. Running the AC on backup power isn't comfort, it's protecting the house itself.
Before the next storm season hits, get your system checked so you know its tonnage and starting watt draw. That number is what determines which generator actually works, and it's worth confirming with a technician who inspects your AC ahead of hurricane season rather than guessing during a storm watch.
How to run your AC during a hurricane power outage
The short version: match your AC's starting watt draw to a generator's surge rating, not its running rating. Here's how the two common paths compare.
| Generator type | Running watts needed | Starting watts needed | Runs whole house? |
|---|---|---|---|
| Portable (gas/dual fuel) | 3,500-5,000 | 10,000-13,000 without soft start | No, AC and select circuits only |
| Portable with soft start device | 3,500-5,000 | 5,000-7,000 | No, AC and select circuits only |
| Whole-home standby (20-24 kW) | 3,500-5,000 for AC alone | Built-in surge handling | Yes, full house including AC |
A 3 ton system draws less than a 5 ton system, so get your unit's tonnage confirmed before shopping for a generator. Verifying your AC's tonnage and specs takes ten minutes and saves you from buying a generator that can't do the job.
Portable generators: 10,000 to 13,000 starting watts needed
A portable generator has to deliver the full surge on its own, and most units in the 8,000 to 10,000 watt running class fall short of what a 3 to 4 ton AC compressor demands on startup. Without help, the compressor tries to draw more current than the generator can supply, the breaker trips, or the motor windings overheat.
A soft start device installed on the compressor ramps the motor up gradually instead of slamming it with full current at once. That single change can cut the required starting watts by close to half, which is why a lot of homeowners add one specifically for generator compatibility, not for everyday performance. Verdict: Buy a soft start device if you plan to run AC on a portable generator. Skip the portable option entirely if you won't add one.
Whole-home standby generators: 20 to 24 kW covers the whole house
A properly sized whole-home standby unit, usually in the 20 to 24 kW range for a typical single-family home, handles the AC's starting surge automatically through built-in load management. It also keeps the refrigerator, well pump, and lights running, which a portable generator dedicated to AC alone can't do.
The tradeoff is installation. A standby generator needs a transfer switch, a gas line or propane tank, and a permit through your county, and Palm Beach, Martin, and St. Lucie counties each handle that permitting a little differently. Verdict: Buy whole-home standby if you want the AC and the rest of the house covered without juggling extension cords during a storm.
Why generator sizing varies
Several things push the wattage number up or down for your specific home:
- AC tonnage. A 2 ton system draws less starting wattage than a 5 ton system serving a larger two-story home.
- Compressor age. Older compressors, including R-22 systems still running in homes built before 2010, often draw more surge current than newer equipment.
- Soft start hardware. Installed or not, this is the single biggest swing factor in required generator size.
- What else runs at the same time. Refrigerators, well pumps, and pool equipment all add to the load a generator has to carry alongside the AC.
- Voltage drop from cord length. Long extension cords between generator and panel lose voltage, which makes starting the compressor harder even on a generator rated big enough on paper.
- Ambient heat. Generators lose some rated output in extreme heat, and running one in direct South Florida sun during a storm affects how close to its rated capacity it can actually perform.
“If the generator can’t deliver the surge watts, the compressor may not start at all, and forcing it can shorten its life.”
Get your AC checked before storm season
A technician can confirm your system’s tonnage and starting watt draw.
Can a 5,000 watt generator run a central air conditioner?
A 5,000 watt generator can run some window or small package units, but it generally cannot start a central AC compressor without a soft start device, since the surge draw on startup typically runs 10,000 watts or higher. Once a soft start device is installed, a 5,000 to 7,000 watt generator becomes workable for smaller systems.
Do I need a whole-home generator for AC in a South Florida hurricane?
You don't need a whole-home generator to keep AC running, but a 20 to 24 kW standby unit is the only option that runs the AC and the rest of the house at the same time without load management decisions. A portable generator with a soft start device can run AC alone on a smaller budget, just not the whole house.
What is a soft start device, and does it really help with generators?
A soft start device ramps an AC compressor's motor up gradually instead of hitting it with full startup current at once, which cuts the required starting watts by roughly half. That difference is often what makes a portable generator viable for AC instead of requiring a much larger, more expensive unit.
While you're thinking about storm prep, it's also worth checking surge protection for your outdoor unit and lightning protection for the condenser. Generators solve the power problem, but a lightning strike or voltage spike during the storm itself is a separate risk to the outdoor unit.
FAQ
How many watts does a central AC need to start on a generator?
A central AC compressor typically needs 10,000 to 17,000 starting watts, well above its 3,500 to 5,000 running watts. A soft start device can cut that starting number by roughly half.
Is a portable generator enough to run my AC during a hurricane?
A portable generator can run a central AC unit if it’s rated for the compressor’s starting surge or paired with a soft start device. Without one, most portable generators in the 8,000 to 10,000 watt class fall short and trip on startup.
What size whole-home generator do I need for AC in Florida?
Most single-family homes need a 20 to 24 kW standby generator to run central AC along with the rest of the house. Smaller homes with lower tonnage AC units may work with less, but tonnage should be confirmed first.
Can running my AC on a generator damage the compressor?
Yes, an undersized generator that can’t deliver full starting watts can strain or damage the compressor if the AC is forced to start repeatedly. Matching generator surge capacity to the compressor’s actual draw prevents this.
Should I install a soft start device before hurricane season?
Installing a soft start device before hurricane season makes sense if you plan to run AC on a portable generator, since it can cut starting watt requirements by close to half. It’s a one-time install, not something to figure out during a storm watch.
Does an old R-22 AC system need a bigger generator?
Older R-22 compressors, common in South Florida homes built before 2010, often draw more starting current than newer equipment, so they can need a larger generator or a soft start device more than a newer system does.
What else besides the AC should a generator power during a storm?
Refrigerators, well pumps, and pool equipment are the next priorities after AC, and each adds to the total load a generator has to carry. A whole-home standby unit handles all of it together, while a portable generator usually means picking which circuits matter most.
One last thing
Most homeowners who get burned by generator sizing didn't buy the wrong generator, they never confirmed their AC's actual starting watt draw before the storm hit. That number takes a technician a few minutes to check, and it's the difference between a generator that works on the first try and one that trips a breaker at 2am during a hurricane in 2026.
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