Whole-Home Standby Generator
Sizing Calculator

How to Calculate Standby Generator Size for Your Home

Choosing the right whole-home standby generator is determined by the simultaneous electrical load of your home's appliances, rather than just the square footage of the house. A large home relying on natural gas appliances often requires significantly less electrical backup power than a smaller home equipped with multiple central air conditioning units, an electric water heater, and an EV charger.

1. Determine Your Base Running Load

The calculation begins with your base running load, which covers essential daily items. For the average Texas home, this baseline ranges from 1,200 to 3,500 watts, providing uninterrupted power for LED lighting, refrigerators, internet routers, televisions, and device chargers.

2. Factor in High-Draw Appliance Loads

Next, we account for heavy-duty appliances that draw significant constant wattage. If you intend to operate electric dryers (approx. 5,500W), electric water heaters (4,500W), or Level 2 EV chargers (7,200W) during an outage, these substantial loads must be calculated into the standby generator's continuous capacity.

3. Account for Compressor Starting Surge

Air conditioning systems are usually the largest determining factor in generator sizing. While a standard 3-ton AC unit might only draw 3,500 watts while running, it demands a massive, split-second surge of power (often up to 10,000 watts) to start the compressor. Sizing is heavily influenced by the Locked Rotor Amps (LRA) to guarantee the generator can handle this initial motor startup without tripping breakers.

4. Incorporate the 25% Safety Margin

A reliable generator should never run at 100% capacity. Pushing a generator to its absolute limit causes overheating and premature engine wear. We automatically factor in a 25% safety buffer so your unit operates comfortably between 50% and 75% capacity, maximizing fuel efficiency and overall longevity.

Frequently Asked Questions: Standby Backup Power

Is it cheaper to power your house with a generator?

No, it is generally much more expensive to power your house with a generator than to use standard utility grid electricity. Using a whole-house standby gas generator as backup equipment doesn't provide economy of scale, whereas the city electrical grid in Montgomery or Harris counties generates power efficiently at massive scales. Standby units are for emergency use and not designed to replace cheap, mass-produced utility power.

How much does it cost to run a generator 24 hours a day?

The cost to run a generator for 24 hours heavily depends on the generator's size and your fuel source. In Montgomery and Harris counties (as of August 2026), running a standby generator costs significantly more than grid power. Here is the estimated 24-hour cost:

• 18kW System: Natural Gas ~$35/day | Propane ~$130/day
• 20kW System: Natural Gas ~$40/day | Propane ~$145/day
• 22kW System: Natural Gas ~$45/day | Propane ~$160/day
• 24kW System: Natural Gas ~$50/day | Propane ~$175/day

How much value does a generator add to a house in Montgomery and Harris Counties TX?

A permanently installed whole-house standby generator typically increases a home's resale value by 3% to 5%. For a $400,000 home, this adds roughly $12,000 to $20,000 in value. High-quality installations connected to a permanent natural gas or propane line often recover 50% to over 100% of their initial installation cost.

Which home generator is better, Generac or Kohler for Texas?

Kohler is generally better for premium quality, quieter operation, and long-term durability with commercial-grade components. Generac is better for budget-friendly pricing and offers a massive local service network, making local servicing and parts much simpler in Texas. Both are top-tier choices for whole-home standby power.

Can neighbors complain about the noise from a generator?

Yes, neighbors can legally complain about generator noise. Homeowners Associations (HOAs) or local authorities can fine you if the noise breaks local decibel rules. HOAs set strict rules and you have to be compliant to them or face fines, despite them often providing zero benefits to your personal privacy. To mitigate this, ensure your standby generator's automated self-tests are scheduled during normal daytime hours.

How big is a generator for a 2000 sq ft house?

To power a 2,000 sq ft house completely, including central air conditioning and major appliances, you typically need a home standby generator rated between 18kW and 24kW. The exact calculation depends heavily on whether your major appliances (like your oven and water heater) are electric or gas.

Can you hook up a generator to your house without a transfer switch?

No, it is dangerous and illegal to connect a standby generator without formal transfer equipment. Per NEC Article 702.4 and 702.5, proper transfer equipment is strictly required to prevent dangerous backfeeding. A Licensed Texas Master Electrician must install an Automatic Transfer Switch (ATS) for a safe, smooth 2-4 second automated startup that brings electricity back to your residential or commercial property.

Last Updated: August 2026