You are standing in the driveway looking at a metal box the size of a suitcase, wondering if it can really carry a house through a hurricane outage. It can — if it is the right size. Too small, and the air conditioner will not start. Too large, and you paid for capacity you will never use, and the unit may run inefficiently at light load.

The short answer

A whole-home generator for a typical single-family home in Palm Beach County sits in the 22–26 kW class. That is the size most of the homes in our county cost range — $11,000–$17,000, installed and permitted — are buying. Three profiles cover most of the houses here:

Essentials + one air conditioner: A smaller unit in the air-cooled standby class, toward the $11,000 end of the range.
Whole house, with the air conditioner running: Typically a 22–26 kW unit. The centre of the county range — $11,000–$17,000, installed and permitted.
Larger home, or a home with heavy electrical loads: The top of the air-cooled class or the step beyond it, toward the $17,000 end.

The number that matters for your home comes from a load calculation, not from a size chart. If an installer quotes a size without asking what is in your house, that is a guess — and this guide exists so you can spot one.

Figures last reviewed November 2026 · Sources: see ‘How we get our numbers’ on the About page.

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How sizing actually works

A generator is sized by load, not by square footage and not by the size of your electrical panel. Two houses of the same size can need very different generators, because the loads inside them are different. The calculation has two parts:

Running loads: the steady draw of everything switched on at once — air conditioner, refrigerator, lights, fans, the well pump if you have one.
Starting loads: the short surge when a motor starts. An air conditioner’s compressor draws several times its running current for a second or two — and if the generator cannot supply that surge, the compressor does not start.
The size that covers both: the generator must handle the highest combined load you will actually run, including the largest starting surge, with margin. That is the number the load calculation produces.
What is not counted: loads you would never run together — the pool heater while the air conditioner is off, for example. A good installer asks about your real usage, not a theoretical maximum.
The automatic transfer switch: sized to the generator, not the house. A 200-amp service does not mean a 200-amp switch.
The panel: if your panel is full or undersized, the installation may include a panel upgrade — $500–$2,000 in the county figures.

The calculation is not complicated, but it is specific. It needs the actual loads in your house — which is why it is done on site, not over the phone.

The load calculation

The installer’s load calculation is a walk through the house with a list. It usually goes like this:

Every motor and every large appliance gets its nameplate rating — the air conditioner (both running and starting amps), the refrigerator, the water heater if electric, the well pump, the pool pump.
Then the loads that run together: the air conditioner plus the refrigerator plus the lights, plus whatever else is normally on at the same time.
Then the loads that do not run together, and the loads you are willing to leave off during an outage.
The result is a number in kilowatts — and a generator size that covers it with margin, not a generator size that happens to be on the truck.

Ask to see the calculation. A written load calculation is the difference between a size and a guess.

Load management

Load management is the reason a 22 kW unit can run a house that, on paper, needs 26. It works by sequencing — the generator starts the air conditioner first, waits for it to settle, then adds the next load, and sheds loads that would push it over. The transfer switch or a separate load-management module does the sequencing automatically.

Two things load management does not do: it does not make a small generator run a large house, and it does not let you run everything at once. It buys you a size class, not a miracle.

Why oversizing costs you money

A generator that is too large for the house costs more to buy, more to fuel, and may wear faster. At light load — a small house on a large unit — the engine runs below its efficient range, and unburned fuel can glaze the cylinders over time. The right size is the smallest unit that covers your calculated load with margin.

The unit itself: a step up in size is roughly $500–$1,500 more at the unit, before installation.
The fuel: a larger unit burns more at the same load.
The wear: light-load running is harder on the engine than the load it was built for.
The range: the whole-home class for this county tops out around 26 kW for air-cooled units. Above that, the price and the installation change — and the number leaves the $11,000–$17,000 range behind.

Why undersizing costs you more

A generator that is too small fails at the worst moment — when the air conditioner tries to start and the voltage sags. The compressor stalls, the breaker trips, or the generator shuts down on overload. The house that was supposed to stay cool goes dark, and the fix is a larger unit — which means paying for the installation twice.

The air conditioner will not start: the starting surge is the load that breaks an undersized unit.
Brownouts damage equipment: low voltage during a start attempt is harder on motors than no power at all.
The upgrade costs more than the difference: replacing a unit means a new pad, new fuel work, and a second permit.

Sizing for a house that runs unattended

If the house will run on generator power while you are away, size for the loads that run themselves: the air conditioner on its thermostat, the refrigerator, the dehumidifier if you leave one running, and any sump or lift pump. The loads you switch on yourself — cooking, laundry, the pool — do not need to be in the unattended number.

Tell the installer the house runs unattended. It changes the load list, and it changes the monitoring conversation — which is why the Cost Guide has a section on it.

Read the snowbird guide: What an outage does to an empty Florida home.

Get the numbers in one file

The free Cost Guide includes the three sizing profiles above with their cost ranges, the load worksheet, and the checklist for your consultation.

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Sizing questions, answered

Can I use an online calculator to size my generator?

A calculator is a starting point, not an answer. It cannot see your nameplate ratings, your panel, or which loads you actually run together. Use it to get a rough range, then let the installer’s load calculation set the size.

Can I size a generator by square footage?

Roughly, and only roughly. Two 2,500-square-foot homes can differ by a pool, a second air conditioner, electric cooking, or a home office. Square footage is a proxy; the load calculation is the number.

What is load management, in one sentence?

The generator starts heavy loads one at a time instead of all at once, so a smaller unit can cover a house that would otherwise need a larger one.

Does a bigger generator use more propane?

It uses more when it is running at load — a larger unit burns more fuel at the same load than a smaller one doing the same work. That is part of why oversizing costs you twice: once at purchase, and again every hour it runs.

What about the pool?

A pool pump is a moderate load. A pool heater is a heavy one. If you want the heater on generator power, say so before the load calculation — it changes the size.

Palm Beach Backup Power is an independent information service. We are not a generator installer. These figures are published estimates, not quotes — the number for your home comes from your installer’s written quote.

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