November 14, 2023

How to Calculate Your Home’s Power Needs for a Generator

Decide What You Want to Power

Whole-house standby generators connect directly to your electrical panel. When an outage occurs, a transfer switch isolates your home’s wiring from the grid, directing power from the generator until power is restored.

Begin by creating a list of critical appliances and devices you want to use during an outage. These could include your HVAC system, refrigerator and freezer, sump and well pumps, essential lighting, and small kitchen appliances. Next, make a secondary list of non-essential but desired items like your TV, radio, and garage door opener. The more devices you add, the bigger the generator you’ll need.

Understand Power Requirements

Each appliance should have an energy usage label specifying its wattage requirements. Be aware that appliances with electric motors—like your HVAC system or sump pump—require more power at startup. Multiply the listed wattage by three for these items. After totaling the wattage, add a 15 to 25 percent margin for error. For instance:

  • Refrigerator: 600W (2800W startup)
  • Freezer: 2500W (4700W startup)
  • Furnace with 1/4 HP fan: 600W (1600W startup)
  • Sump pump with 1/3 HP pump: 500W (1700W startup)
  • Microwave: 1000W
  • Coffee maker: 850W
  • 10 LED light bulbs: 9W each (90W total)
  • TV: 300W
  • Garage door opener with 1/3 HP motor: 725W (1400W startup)

The total wattage for the above systems is 13,240W, or about 13.2kW. Including your safety margin, a 15kW to 16kW generator should be appropriate.

Make Changes or Select a Generator

Generators come in various sizes. Based on your calculations in the previous step, you may need power in one of the following ranges:

  • 7kW to 12 kW: Power only the essentials with a small, economical generator.
  • 13kW to 26kW: Enjoy mid-range power for a moderate price.
  • 27kW to 150kW: Go all-out for your luxury home, estate, or small business.

If your calculations point to a larger, more expensive unit than you would like, consider revising your power requirements. Remember, you won’t run the furnace and air conditioner simultaneously, which should lower your needs. Always aim for a little more than the bare minimum to give yourself room for future growth.

Get Help Sizing a Backup Generator

While this guide is a good starting point, the best way to calculate generator size is to examine your specific appliances and devices. Then, reach out to Seidel Electric Inc. We can recommend the proper generator size to meet your family’s power requirements during a blackout. We also perform expert installations with customer satisfaction guaranteed. For more information or to schedule services in the Tri-State Area, please call us at (908) 362-6191 today.