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What Size Generator Do I Need to Power My House During an Outage?

[fa icon="calendar"] Oct 18, 2017 10:27:17 AM / by Jaron Henkel

In September, Hurricane Irma threw the Southwest Florida area into a panic as the reality of the necessity of hurricane preparedness and power outage preparedness became all too evident.

Right now, as things begin to normalize, our power is restored, and we recover, considering what you might need for the future should be at the forefront of your mind. After this past month, investing in a backup generator is probably something you are considering. But where do you start? Read on as we explain generator sizes and what they power to help you figure out “watt” you need.


Generator Size: What Does That Mean?

When talking about generator size, we aren’t talking about it’s physical size – rather, the size refers to how much electrical power it can supply, measured in watts (W) or kilowatts (kW). What happens if you get the wrong size? Getting an improperly sized generator for your needs can be a costly mistake!

Go too small, and you may not have enough voltage to properly power your appliances. This can damage your appliances and your generator, resulting in expensive repairs and even replacements. On the other side of the coin, go too big, and you’ll basically throw money away by unnecessarily overpaying for both the unit and the operation costs. So, what’s a homeowner to do? Follow these three steps to ensure you’ll be getting just the right generator for your needs;

3 Steps to the Right Size Generator

Step 1: Make a List (and check it twice?) - Make a list of all the appliances you would want powered in the event of an outage. Be realistic but inclusive. Here in Southwest Florida, most people would make the air conditioner a high priority, along with refrigerator. Don’t forget smartphone charging and at least a few light fixtures when making your list. Whether you choose to stick with the essentials or go for full home coverage, you’ll need to be thorough with your list.

Step 2: Determine the Draw - Next, you’ll need to figure out how much wattage each appliance or light fixture will need. Most appliances will have this information stamped or on a sticker, found where the serial number and service information is indicated. More information on where to find the exact wattage details on appliances and an easy to use energy use calculator can be found on the US Department of Energy’s Energy Saver website. Using their calculator for this purpose, you are only concerned with the wattage. Please note that this tool provides a sample value only, refer to your specific appliance for an exact reading.

Step 3: Add it Up - The hard work is done, now simply add the wattage of the appliances on your list to find the total wattage needed and determine the base level generator you need from that number.


The EASY Way

Generac, a leader in home backup generators and one of the brands Southwest Florida Electric proudly sells, services, and installs, has an easy-to-use online tool that will help you quickly estimate the size generator you will need for your home, based on your selected appliances, lighting, and extras - or you can simply select “whole home” for an idea on what it would take to power your whole home. Simply follow the prompts in the Generac Home Backup Generator Sizing Calculator to get an idea of what size you may need.

Example: A Tale of Two Homes

John and Jeanette Wilson and the Jones Family both have about 2,000 square foot homes in the Naples area, but have different ideas on what they want covered if there is a power outage.

John and Jeanette want to only power the “essentials” if the power is out. They want to stay comfortable with AC and hot water, but don’t necessarily want to keep their whole house at full running capacity. Here’s their list:

  • 2 Light fixtures - 175W (far less if they are using LED bulbs)
  • Electric Water Heater - 4000W
  • Central A/C - 4500W
  • Refrigerator - 1500W
  • Phone and tablet charging- 30-50W


The Wilsons should look at an 11kW home backup generator. With an 11kW backup generator, they should be able to run their basics, keeping themselves comfortable, and their food cold and safe from spoilage.

The Jones family wants to power their whole home up, as if there were no outage. They also made a list of the appliances and devices they want powered (it’s a bit longer than the Wilson’s):

  • 15 Light fixtures - 1225W
  • Electric Water Heater - 4000W
  • Central A/C - 4500W
  • Refrigerator - 1500W
  • Phone/tablet charging - 50W
  • 2 Laptop computers - 150W
  • Microwave - 1000W
  • Stove/Range - 3000W
  • Dishwasher - 1500W
  • Clothes Washer - 1500W
  • Clothes Dryer - 1500W
  • 3 LCD TVs - 450W
  • WiFi & Cable Modem - 40W
  • Garage Door Opener - 2300W


The Jones should consider a 25kW generator to power their whole home. There are 22kW backup generators that we carry, but again it is always best to round up – opt for the generator that offers the next step above your estimated kilowatt needs, not below.

Keep in mind that while these numbers should be pretty close, they are still an estimate. Contact the professionals at Southwest Florida Electric to schedule an in-home estimate, where we can evaluate and calculate your home’s electrical needs and recommend the best size backup generator to keep you up and running, at whatever level of power you prefer. We’ll walk you through the process, from estimate to installation, and even scheduled maintenance as needed.


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Topics: Generators

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