Generators are rated in watts. But your home puts two different demands on them, and only one shows up on most charts.

Running watts is what an appliance draws while it operates. Your refrigerator settles into a steady pull. Your lights hold the same draw all evening.

Starting watts is the surge an appliance needs in the first second it turns on. Anything with a motor spikes hard, often several times its running draw. Your air conditioner is the worst of them.

Here is the formula:

• List every appliance you want running during an outage
• Add up the running watts of everything on that list
• Identify the one appliance with the highest starting wattage
• Add that single surge number to your running total
• Add roughly 20% on top for headroom

You only add the highest surge, not all of them. Your appliances will not all kick on in the same instant.

That last step is not optional. A generator running at its absolute limit has nothing left when demand moves. Overloading a generator is a fire hazard, not just an inconvenience.

The result is your minimum. Anything smaller will fail you at the worst moment.

The formula only works if you have real numbers. Here is what your appliances actually pull.

Your central air conditioner is the largest electrical load in most homes. It draws roughly 3,000 to 5,000 running watts. When it starts, that surge climbs to somewhere between 7,000 and 9,000 watts.

Read that again. The startup surge on one appliance can nearly double your entire running load. That single number usually decides your generator size.

Finding your wattage is straightforward. Check the label on the appliance itself, or open the owner's manual. Both list the running watts. Many list starting watts too.

Now sort your list into two piles.

Must-have loads:

• Refrigerator and freezer
• Heating and cooling
• Critical lighting
• Medical equipment
• Security system
• Well pump, if you have one
• Router and phones

Nice-to-have loads:

• Hot tub
• Workshop tools
• Outdoor lighting
• Home theater

The hot tub is not a must-have. Neither is the pool pump. Every item you move out of the first pile is capacity you do not have to buy.

Be honest about the first list, though. Cutting your air conditioning to save on generator size is a trade most Fort Worth homeowners regret in August.

Now you have a number. Square footage is how you check it.

Find your home in that table. Does it land near the number your calculation produced?

If the two agree, your math is probably sound. If they are far apart, something in your list needs a second look.

Use this as a check, not a calculation. Square footage tells you nothing about what is inside the house.

A 2,000 square foot home with two air conditioners and a workshop can outrun a 3,500 square foot home with one system and gas heat. The bigger house is not always the bigger load.

Your appliances decide your generator size. The square footage just tells you whether your answer is in the right neighborhood.

There is a question underneath the sizing question. Can your electrical panel even carry a generator?

Fort Worth has a lot of older housing stock. Many of those homes still run 100-amp service. That was plenty when they were built. It is often not enough today.

If your panel is at 100 amps, a whole home generator may require a panel upgrade before anything else happens. That changes the scope of the project, and it changes the order of operations.

Newer construction runs differently. Homes built in recent decades typically have 200-amp service and natural gas already run to the house. Those installs are usually cleaner, with no panel work required.

Aging panels bring their own issues. Old breakers, outdated wiring, and panels that are already full leave no room for a transfer switch.

Here is what to look at before you shop for a generator:

• Your service size, listed on your main breaker
• The age and condition of your panel
• Whether your panel has space for a transfer switch
• Whether natural gas is already run to the house

Natural gas is widely available across Fort Worth. That matters, and it shapes the next section.

Answer the panel question first. A generator sized perfectly for a panel that cannot hold it does you no good.

Ready to find out what your home needs? We handle whole home generator installation in Fort Worth and will check your panel before we size anything.

One more thing changes your number, and almost nobody mentions it.

The wattage printed on a generator assumes gasoline. That is the fuel it was rated on. Run it on anything else, and you get less.

• On propane — output drops about 10%
• On natural gas — output drops about 10 to 15 percent

Most whole home standby generators in Fort Worth run on natural gas. The gas line is already at the house, so it makes sense. But that means the label number is not your working number.

Do the arithmetic. A unit advertised at 20,000 watts may deliver closer to 17,000 on natural gas. If your calculation landed at 18,000, that generator will not carry your home.

Factor the reduction in before you choose a unit, not after. Sizing up on paper is cheap. Replacing an undersized generator is not.

This is the mistake we see most often. The math was right. The fuel was not accounted for. The NFPA 70 National Electrical Code governs how generator installations must be sized and connected — the same standard your Fort Worth permit and inspection are judged against.

A calculation on paper is a good start. An assessment in your home is the answer.

Here is what our electricians check when we visit your Fort Worth home.

Your panel and service size — This comes first, because it is the thing most likely to change your project. We read your main breaker, check the condition of the panel, and confirm whether it has room for a transfer switch.

Your HVAC systems — We record the tonnage of each unit and how many zones you run. That startup surge drives more of the sizing decision than anything else in the house.

Your gas line — We measure the line size and the distance from your meter. An undersized line starves the generator under load, no matter how well you sized the unit.

Transfer switch requirements — We identify the switch type your home needs and where it goes.

Permits and inspection — Generator installation in Fort Worth requires a permit and a final inspection. We handle the paperwork and coordinate with the City of Fort Worth.

We install and service standby generators from all leading manufacturers, including Generac, Kohler, and Cummins. Our team will match the right unit to your home, your panel, and your fuel.

The assessment is free. So is the quote. You get a real number for your home, not a guess from a table.

Bringing 50 years of Berkeys expertise to Fort Worth.

Stop guessing at watts. Our licensed electricians will read your panel, measure your load, account for your fuel, and give you a firm number.

Learn more about our Fort Worth team and the electrical, plumbing, and A/C services we bring to Fort Worth and Arlington.

Call (817) 799-6090 to schedule your free generator sizing consultation.

Business Address: 3001 W 5th St Suite 700, Fort Worth, TX 76107
Customer service available 24/7.