How to Size a Generator for Your Home: A Central Florida Sizing Guide

Key Takeaways • Sizing a generator is a math problem, not a guess. It comes down to your home’s total running watts, starting watts, and whether you want whole house or essential circuits coverage. • Central air conditioning is usually the single biggest load in a Central Florida home, and it drives the starting watt surge a generator has to handle. • A licensed electrician’s load calculation catches details a generic online generator wattage calculator cannot, protecting you from a system that is oversized or undersized.

Home Size (Square Feet)	Coverage Goal	Approximate Generator Size
Under 1,500 sq ft	Essential circuits only	7 to 12 kW
1,500 to 2,500 sq ft	Essential circuits plus one AC zone	12 to 18 kW
2,000 to 3,000 sq ft	Whole house with one central AC system	20 to 26 kW
3,000+ sq ft, or multiple AC systems, a pool pump, or an EV charger	Whole house, full coverage	26 to 48 kW

Why Generator Sizing Is More Than Picking a Number

If you already know you want a standby generator, chances are you have searched for what size do I need and landed on a chart with three or four round numbers. That chart is a starting point, not the answer for your specific house.

Central Florida homes carry a heavier electrical load than homes in milder climates, mostly because of air conditioning. A generator that would be plenty for a home up north can come up short here the moment the AC compressor kicks on.

This guide is about the math behind sizing, not whether you should get a generator in the first place. If you are still weighing that decision, our article on Do I Really Need a Whole House Generator in Central Florida walks through it. This one assumes you already said yes and now need the right number in kilowatts.

How to Size a Generator for Your Home Step by Step

Every generator sizing conversation starts with two numbers: running watts and starting watts.

Running watts is what an appliance or circuit draws once it is operating normally. Starting watts, sometimes called surge watts, is the short burst of extra power many motors need the instant they switch on. Central air conditioners, well pumps, and refrigerators all have a starting watt draw that is noticeably higher than their running watt draw.

Here is the basic process for a load calculation for generator sizing:

1. List every circuit or appliance you want the generator to power.

2. Write down the running watts for each one, using appliance labels, spec sheets, or manufacturer data.

3. Add all the running watts together for your total running load.

4. Identify the single largest starting watt draw on your list, almost always the central AC compressor, and add its extra surge on top of your total.

5. Divide the final number by 1,000 to convert it to kilowatts.

That total is your rough minimum generator size in kW. Many homeowners run this math through a generator wattage calculator online first, which is a fine starting point. As you will see further down, it should not be the final word.

Feature	Whole House Coverage	Essential Circuits Coverage
What it powers	Every circuit in the home, including central AC, all at once	Only the circuits you and your electrician choose in advance
Typical generator size	Larger, often 20 kW and up	Smaller, often 7 to 14 kW
Typical cost	Higher equipment and installation cost	Lower equipment and installation cost
Best fit for	Homeowners who want no compromise during an outage	Homeowners focused on essentials such as refrigeration, a well pump, medical equipment, and some lighting

Whole House Generator Sizing vs Essential Circuits Generator Sizing

Once you have a wattage number, you face a second decision: do you want whole house generator sizing, where the generator can carry your entire electrical panel, or an essential circuits generator setup that backs up only the loads you choose?

Whole house coverage means every circuit works during an outage the same way it does on utility power. Central air, both refrigerators, the pool pump, the garage door, all of it. This requires a larger generator and, in most cases, an automatic transfer switch that can manage the full panel.

Essential circuits coverage means you and your electrician agree on a shorter list. Refrigerator, well pump if you have one, a few lights, medical equipment, maybe a single AC zone instead of the whole system. It typically costs less to install and often allows for a smaller, less expensive generator.

Neither option is automatically right or wrong. It depends on your budget, how long outages typically run in your part of Central Florida, and what you genuinely cannot do without.

The type of transfer switch also plays into this decision. Our breakdown of Manual vs Automatic Transfer Switch: Which One Does Your Home Need goes deeper into how that piece fits with whole house versus partial setups.

How Square Footage, HVAC Size, and Major Appliances Change the Math

Square footage gets used as shorthand for generator size, but it is really a stand in for what usually lives inside a home that size: more air conditioning tonnage, more appliances, more circuits.

Central AC and generator size for central AC

Air conditioning is typically the single biggest electrical load in a Central Florida home, and it runs for most of the year here. A larger home usually means a larger AC system, and a larger AC system means a bigger starting watt spike the generator has to absorb the moment the compressor cycles on. This is why two homes with the same square footage can still need different generator sizes if one has a bigger, or older and less efficient, AC system.

Other major appliances that affect sizing

• Electric water heaters and electric ranges add meaningful running watts to the total.
• Well pumps, found on some properties in the region, carry their own real starting watt spike.
• Pool pumps, common across Orlando and Winter Park area homes with backyard pools, add both running and starting load.
• EV chargers add a large, steady running watt draw if you want them backed up during an outage.

None of these details show up on a generic square footage chart. They only show up once someone adds up your home’s actual equipment.

Why Oversizing and Undersizing Both Cost You

It is tempting to just buy the biggest generator available and stop worrying about the math. That approach has a real cost, and so does the opposite mistake.

The cost of oversizing

• You pay more upfront for capacity you are not using.
• A generator running well below its rated capacity for long stretches is not necessarily the efficient choice it seems. Fuel use per hour of useful output can be worse than with a correctly sized unit.
• Installation costs, including the transfer switch and fuel supply line, tend to scale up with generator size too.

The cost of undersizing

• The generator can trip or shut down when the AC compressor starts, right when you need it most.
• You end up manually shedding loads during an outage, unplugging things or flipping breakers to keep the unit from overloading.
• Repeated overload cycles can shorten a generator’s working life over time.

The goal is a number that comfortably covers your real load with a reasonable buffer. Not the largest generator on the lot, and not the cheapest one either.

Why a Licensed Electrician Should Run the Final Load Calculation

Online generator wattage calculators are a genuinely useful first step. They are not a substitute for a load calculation done by a licensed electrician, and here is why.

A proper load calculation accounts for your actual panel, your specific appliance nameplates, your home’s wiring, and applicable code requirements under the Florida Building Code, which currently adopts the 2023 NEC with state amendments.

An online tool cannot see any of that. It only knows what you type in, and most homeowners are estimating at least some of those numbers.

An electrician will also check details that change the outcome:

• Whether your existing panel and electrical service can support the transfer switch and generator you are considering.
• Diversity and demand factors that a simple addition of appliance wattages does not account for.
• Local permitting and inspection requirements for standby generator installations across our Central Florida service area.

Getting this step done properly is the difference between a generator that quietly does its job for years and one that becomes a source of frustration during the next storm.

Step	What Happens
1	List every circuit and appliance you want powered during an outage.
2	Record the running watts and starting watts for each major item, especially the central AC system.
3	Add the running watts together, then check the single largest starting watt spike against your total.
4	Decide between whole house and essential circuits coverage based on budget and priorities.
5	Have a licensed electrician verify the number with a formal load calculation before you purchase a generator.

Frequently Asked Questions

What size generator do I need for an average Central Florida home?

There is no single answer without a load calculation, but many Central Florida homes with one central AC system and standard appliances fall somewhere in the ranges shown in the sizing table above.

Can I use a free online generator wattage calculator instead of hiring an electrician?

A generator wattage calculator is a good way to get a rough range before you start shopping. It should not be the final word, because it cannot verify your panel capacity, actual appliance nameplates, or code requirements the way a licensed electrician’s load calculation can.

Is it better to oversize a generator just to be safe?

Not usually. Oversizing means paying for equipment and installation capacity you do not need, and running a generator well under its rated capacity for long periods is not always the efficient choice homeowners assume it is. A properly sized unit with a reasonable buffer is generally the more practical choice.

Getting Your Generator Size Right the First Time

Sizing a standby generator is not guesswork. It is arithmetic plus judgment about what matters most to your household during an outage. Add up your real running and starting watts, decide between whole house and essential circuits coverage, and factor in the true load of your AC system and major appliances.

Once hurricane season arrives, that is not the time to discover your generator was sized for a different house. If you already have a generator installed, keeping it ready matters just as much as sizing it correctly. Our Generator Maintenance Tips for Hurricane Season article covers what that upkeep involves.

InPhaze Electric has been doing electrical work across Orlando and Central Florida for more than 30 years, and getting the load calculation right the first time saves homeowners money and headaches down the road.

Ready for the right generator size, not a guess? InPhaze Electric helps homeowners across Orlando, Winter Park, Maitland, Longwood, Lake Mary, Winter Garden, College Park, and Conway with accurate load calculations and standby generator installation. Call us today to schedule a professional load calculation before you buy, so the size you choose actually matches your home.