Standby Generator Sizing: What Size Does Your Home Need?

Many people shop for a generator by asking what size they need, as if it were a shoe size. The better first question is what you want the generator to do. Do you want to keep the refrigerator, a few lights and the internet going? Do you want the air conditioner running through a hot Houston outage? Do you want everything in the house to work as if nothing happened?

The answer shapes everything that follows. A generator that is too small may shut down on overload or struggle to start a large motor. One that is far larger than you need costs more up front and may be a poor fit for your fuel supply. Good sizing lands in between, with some room to spare.

There are two common approaches. In an essential-circuits setup, the generator powers a chosen group of circuits, such as the refrigerator, lights, outlets in key rooms, the furnace or air handler, a well pump if you have one and maybe one air conditioner. In a whole-house setup, the generator is sized to carry nearly everything, including multiple air conditioners, an electric range, a dryer and a water heater.

Neither is wrong. Essential circuits generally call for a smaller unit, while whole-house coverage gives up nothing but asks more of the generator and the fuel supply. We help you decide which fits how your family lives, then size to that decision. Load management devices can also help a smaller generator share its power among big appliances, which is something to ask about during your consultation.

Air conditioning is usually the biggest factor in this part of Texas. The tonnage of your system tells us how much it draws while running, and an older or larger system can pull much more when it starts. If your home has two or three systems, that changes the math quickly.

Starting loads, also called surge or locked-rotor demand, are the next piece. Motors, such as air conditioner compressors, well pumps and some pool equipment, draw a burst of power for a moment when they kick on, well above what they use once running. A generator has to handle that burst, not just the running number on the label. There are ways to soften it, including soft-start devices on air conditioners, and we can talk through whether they make sense for your home.

Other loads count too. Electric water heaters, ranges, dryers, EV chargers and pool equipment all add demand. A home with gas appliances has a lighter electrical load than an all-electric one of the same size.

A load calculation lists every circuit or appliance you want covered, finds how much each draws when running and when starting, and then works out what could be on at the same time. Not everything runs at once, so a professional uses judgment about realistic overlap while still leaving a safety margin.

The result is a generator capacity that carries your chosen loads and handles the biggest motor starting while everything else is running. It also considers your electrical service and panel, since the generator connects through a transfer switch that has to match your service. This is why a calculation done from a satellite photo or a rule of thumb is unreliable.

The fuel affects how much power a given generator model can deliver and how much fuel the site can supply. Natural gas depends on your meter and the pipe feeding the house, which may or may not have capacity for a generator on top of your other gas appliances. Propane depends on tank size. We check both during the site visit so the unit you choose can actually be fed. We cover this tradeoff in more depth in our guide to natural gas versus propane standby generators.

Sizing is not just math. It involves electrical code, the capacity of your service, the gas supply and the way your particular home is wired. A mistake can mean overloaded equipment, a generator that cannot start your air conditioner, or a transfer switch that does not match your panel. A licensed electrician who looks at your home in person can catch those issues before they become expensive.

Online sizing charts and calculators can help you get oriented, but treat them as a starting point. We recommend using one to build a wish list, and then having a professional verify it.

Call Wired Electrical & Generators at (713) 467-1125 for a free estimate. We are a family-owned, licensed and insured electrical company in Tomball, TX, serving the Houston area.