What Size Standby Generator Does My Houston Home Need?

Most Houston homes need a standby generator between 18 kW and 26 kW to power the whole house, including central air conditioning. Homes that only back up the essentials often land between 10 kW and 16 kW. Larger homes with two AC systems, a pool pump, or an EV charger may need 26 kW or more.

Here is how those ranges break down:

Four things move your number inside these ranges:

• The size of your central AC and the surge it pulls at startup
• How many circuits you want backed up during an outage
• Your fuel type, natural gas or propane
• Future loads, like an EV charger or a room addition

Treat these as a starting point. They give you a range to talk through, not a final answer.

In Houston, backup power without air conditioning is not really backup power. Summer outages are a heat problem before they are a comfort problem. Your AC is also the single largest load your generator has to carry.

A standard 3-ton central system pulls roughly 3,500 to 5,000 running watts. The startup surge can hit several times that figure for a fraction of a second. That brief spike is what trips an undersized generator.

Here is what that means in practice:

• One central AC system sets the floor for your kW range
• Two systems roughly double the problem and usually move you up a tier
• The surge, not the running load, is what your generator must survive

There is a way to soften it. A soft-start device limits the inrush current when the compressor kicks on. On some homes, that lowers the surge enough to make a smaller unit workable. It is worth asking about before you settle on a size.

If your AC has to run during an outage, size for the surge. Everything else in the house is easier to cover.

You can get close to your number in about twenty minutes. Here is the method we use as a starting point.

1. List what must stay on — Walk the house and write down every load you cannot go without. For most Houston homes that means the AC, refrigerator, freezer, lights, outlets, and the water heater. Add a well pump, sump pump, or medical equipment if you have them.

2. Find the running watts on each one — Most appliances carry a label or data plate with a wattage rating. Some list amps and volts instead. Multiply those two together to get watts.

3. Add the running watts together — This gives you your continuous load. It is the power your home draws while everything is already on.

4. Add the largest starting surge on top — Only one motor surges at a time in most cases. Take the single biggest starting load, usually your AC, and add it to the continuous total. That number is your peak.

5. Convert to kilowatts and add headroom — Divide your peak watts by 1,000 to get kW. Then leave room for what you may add later, like an EV charger or a home addition.

Your result is an estimate, not a final spec. It tells you which range to plan for and what questions to ask.

Your fuel source changes both how the generator runs and how much power it makes. Most Houston homes run on one of two options.

Natural gas is the common choice across Houston's established neighborhoods. The line is already there, so there is no tank to fill and no fuel to run out of. In most outages here, the gas stays pressurized even when the grid is down. That lets the unit run for days.

Propane is the answer when a gas line does not reach your property. It works well, but the tank size matters. A multi-day outage burns through fuel, so the tank has to be sized for the length of outage you expect.

Two details catch homeowners by surprise:

• Generators produce less output on natural gas and propane than they do on gasoline. Your kW rating shifts with the fuel.
• Your gas meter has to deliver enough volume to feed the unit. A meter sized for a furnace and a water heater may not be enough for a 24 kW generator.

Both are worth checking early. A fuel supply that cannot keep up will limit the generator you can install.

Sizing errors cut both ways. Neither one shows up until the power is already out.

Too small is the failure most homeowners fear. The unit cannot absorb the AC startup surge, so it trips. You get nuisance shutdowns at the exact moment you need the power. A generator running near its limit for days also wears faster than one running in its comfort zone.

Too large creates a quieter problem. The unit spends its life at low load, and engines do not like that over the long run. Light loading is hard on the machine and shortens the life you paid for. You also bought capacity you will never touch.

There is a middle path worth knowing about. A load management system sheds low-priority circuits when demand spikes. It can let a smaller generator cover a larger home. That often means a right-sized unit instead of an oversized one.

Getting the number right the first time is what protects the equipment. It also protects the money you put into it.

Your estimate gets you a range. A load calculation gets you the number. Here is what happens when we come out.

We start at the panel — We look at your service size, your breaker layout, and the condition of the equipment. Older Houston homes sometimes need panel work before a generator can tie in at all.

We run the calculation to code — The National Electrical Code sets the standard for residential load calculations. That is what your permit and inspection are measured against, not a rule of thumb.

We size the transfer switch — The switch is what disconnects your home from the grid and connects it to the generator. It has to match both the unit and the circuits you want backed up. Placement matters too.

We check the fuel supply — That means confirming your gas meter can deliver the volume your unit needs, or sizing a propane tank for a multi-day outage.

We handle permits and inspection — Houston requires electrical permits for a generator install, and gas work may need its own. We file them and meet the inspector.

Ready for a real number for your home? We can size and install your standby generator.

Abacus Plumbing, Air Conditioning, & Electrical
Business Address: 4001 Kendrick Plaza Dr, Houston, TX 77032
Open 24 hours, seven days a week
Serving The Woodlands, Spring, Humble, Kingwood, Tomball, Klein, Atascocita, and North Houston
Call (713) 812-7070