Every September we run a wave of calls from homeowners who just had a multi-day outage and discovered their generator could not actually run the AC - or could, but tripped under load whenever the kitchen and the well pump came on at the same time. The fix is usually not a bigger generator. It is the right answer to "what is the generator size for AC Florida homes," paired with a soft-start kit on the compressor and a transfer switch that is programmed honestly. Here is the mechanical reality most installers do not put in writing.
Locked-rotor amps: the number that actually matters
Generators are sized in kilowatts, but compressors care about locked-rotor amps (LRA) - the inrush current the motor pulls in the first half-second of startup before it spins up. Running amps are modest; LRA is anywhere from 5 to 8 times running. A typical residential compressor:
- 2-ton: 12–14 running amps, 60–80 LRA
- 3-ton: 16–20 running amps, 80–110 LRA
- 4-ton: 22–26 running amps, 110–140 LRA
- 5-ton: 28–32 running amps, 140–170 LRA
The exact LRA is on the data plate on the side of your condenser. A generator that can deliver the running amps fine may sag voltage so badly during the LRA spike that the compressor never starts - it just hums, the start capacitor takes the heat, and after a few attempts the breaker on the generator trips.
kW per ton rule of thumb
Without a soft-start kit, the standard sizing rule for whole-home standby generators is:
- ~2 kW per ton of cooling for the AC alone (so a 3-ton needs about 6 kW just for the compressor surge headroom)
- Plus ~3–5 kW for the rest of the protected loads on a typical Florida home (lights, refrigerator, well pump, internet)
- Plus ~3 kW if you also want to run the electric water heater or the cooktop
That puts most 3-ton homes in our area at 14 kW minimum, 18–20 kW comfortable. A 4-ton home is 18 kW minimum. The 11 kW units you see at big-box stores are sized for emergency loads only - they will not carry the AC.
Soft-start kits: what they actually do
A soft-start kit is a small electronic module wired into the compressor's start circuit that reduces locked-rotor inrush by 60–70%. Instead of pulling 110 LRA for half a second, a 3-ton compressor with a soft-start pulls 35–45 amps. That changes the math entirely:
- A 9–11 kW generator can suddenly carry a 3-ton AC that it could not start without the kit.
- A portable generator (Honda EU7000iS, Champion 8.5kW) becomes a viable hurricane backup instead of a "everything but the AC" device.
- Compressor life improves independently of generator use. Lower inrush means less wear on every start cycle.
The two kits we install most:
- Micro-Air SureStart. The default. Auto-sensing, works on most single-phase residential compressors, $400–$550 installed.
- Hyper Engineering MicroAir. Comparable performance, slightly different installation. We install whichever the customer prefers.
Installation is roughly 90 minutes - kill power, open the condenser, wire the module in series with the existing run capacitor, restore. Not a DIY job because compressor terminals carry capacitor charge that will hurt you if you skip the discharge step.
Whole-home standby vs portable: the honest tradeoffs
Generac, Kohler, and Cummins all make solid 14–22 kW air-cooled standby units that auto-start within seconds of an outage. They run on natural gas or LP. Pros: hands-off, sized to carry the AC, no fuel hauling. Cons: $10,000–$15,000 installed, annual service required, sit unused most of the year.
Portables (Honda, Champion, Westinghouse 7–10 kW) cost $1,500–$3,500 and can carry an AC with a soft-start. The cons are real: gasoline storage, manual start, manual transfer, theft risk, exhaust placement (carbon monoxide kills people every storm season - never run a portable in the garage, period).
The right answer depends on how often you ride out storms in the house versus evacuate. A primary residence in Punta Gorda Isles or a coastal Cape Coral home that the family stays in - whole-home standby. A second home that you secure and leave - a portable with a soft-start is reasonable.
The transfer switch question installers gloss over
This is the part that bites homeowners. Generators do not automatically power every circuit in the house - they power whatever is on the protected-loads side of the transfer switch. Some installers, to save panel space or to keep generator runtime modest, exclude the AC circuit from the protected loads. They do not always tell the customer.
Two things to verify with your installer in writing:
- Is the AC on the transfer switch? Check the panel labeling. If the AC breaker sits in the main panel and not in the protected sub-panel, it does not run on generator.
- Is the AC load-shed at all? Some smart transfer switches drop the AC if other loads exceed a threshold. That is a feature, but you should know it exists.
Common installer shortcuts to look out for
- "You can run the AC on this 11 kW unit." Maybe, with a soft-start. Without one, no.
- No soft-start quoted on a marginal generator pairing. If your generator is at the low end of the kW-per-ton math, discuss whether a soft-start belongs in the proposed installation scope before relying on the generator during a storm.
- No load test under summer conditions. A generator that cranks fine in February may sag under a 95F afternoon load. Annual load tests are worth doing in May, not in October.
- AC excluded from protected loads without disclosure. Read your panel schedule.
When to call us
We size soft-start kits and verify generator/AC compatibility across Punta Gorda, Punta Gorda Isles, Port Charlotte, North Port, and Cape Coral. If you are about to buy a generator and want a real LRA reading on your existing condenser, or if you have a generator that cannot start your AC and want to know whether a soft-start fixes it, call (941) 205-6331 or request service. Diagnostic visit is $99. License CAC1824348.