How Big of a Generator Do I Need for My House?

Hurricanes and severe storms that barrel across Florida often leave residents without power for weeks, months, or even longer. A recent supply chain issue meant replacing transformers took much longer than usual, and it doesn't look like these issues are going to get resolved any time soon.

Having a reliable whole-home generator is more crucial than ever. But have you ever asked yourself, "how big of a generator do I need?"

You want a generator that can meet all of your electrical demands, and that means considering wattage and run time.

Determining Wattage

To calculate the right generator size for your home, you need to know the wattage of the appliances and devices you want to run on the generator.

A good formula to follow is Running Wattage + Starting Wattage = Total Wattage Needed.

Here are some common approximate wattage numbers:

Window AC: 600-1,500
Central AC: 2,000-4,000
Sump Pump: 1,500
Refrigerator/Freezer: 600-1,000
Electric range: 2,500
Microwave: 1,200
Coffee maker: 400-800
Space heater: 1,250
Lamp: 150
TV: 100-500

Keep in mind these are approximate numbers. If you want a better estimate, talk to a professional about your electric needs.

Running Wattage vs. Starting Wattage

Check the owner's manual for your appliances to find the exact running wattage. Starting wattage is usually three times the amount of running wattage.

For example, if you want to power a window AC unit with a running wattage of 600 watts, the starting wattage would be 600 x 3 or 1,800 watts. So, the formula would be:

600 + 1,800 = 2,400 watts.

A good rule of thumb is to choose a generator that can handle powering all of your appliances without using more than 90% of its capacity. If your electrical needs are too much for your current generator, it might be time to get a replacement.

The Size of Your Home and How You Plan to Use It

The size of your home and the number of appliances you want to keep powered should factor into your decision. Even the best whole-home generators won't be able to keep your devices powered on if you choose a model that doesn't have the capacity to cover the wattage you need in your entire home.

When shopping for an emergency generator, you need to decide if you only plan to use it for a few days and to power a few appliances or if you want it to power most or all of the devices in your home.

Generally, running the most critical home equipment takes a generator rated at between 5,000 to 7,500 watts. Again, you want to buy a generator that's slightly bigger than your needs. If you want to power most of the appliances at home during an outage, you'll want a generator rated for around 10,000 watts.