Standby Generator Sizing

When getting a generator for your house or business, you should get one that supplies more power than you need. However, getting the right amount of power can be a daunting task given that getting one that’s too big will be a waste of money in terms of purchasing and running costs.

The good news is you can find generators from as little as 800 watts all the way to 500,000 watts or more. Even with this wide range, you need a good understanding of how much power your appliances need before buying the standby generator. You also need to understand the various types of wattages for the appliances to ensure the generator accommodates all of them.

In this guide, we assess the various aspects that go into choosing the right size of standby generator. The pointers in this guide hold for both home standby and commercial standby generators since all that matters is the power needed by your appliances.

What is Starting, Running and Surge Wattage?

You need to first understand the wattages written on your appliances with their meanings being as follows:

  • Starting Wattage: this is the amount of power an appliance needs to start from the off position. It’s usually about 3 times the amount of power you need to run the device.
  • Running Wattage: this is the amount of power the appliance needs to keep running.
  • Surge Wattage: this is the highest amount of power you can get from the generator.

With these wattages in mind, head to the next step below.

Calculating the Size of Generator Needed

Home standby generator
Champion Standby generator

First, identify the appliances you need to power up with your generator as the first step. For each device, identify the starting wattage which is either written on the appliance or in the manual. to find the total power the device needs, use the following formula:

(Running Wattage x 3) + Starting Wattage = Total Wattage Needed.

For example, an appliance with a starting wattage of 300W will need the following total watts:

(300×3) + 300= 900 + 300 =1200 Watts

For such an appliance, you need a generator that produces at least 1500 Watts to be on the safe side.

To find the total amount of watts your generator needs to produce, you should add all the needed watts for each appliance. The total will give you the sum total of the watts needed.

Some common home appliances and their wattages are as follows:

Refrigerator/Freezer600 to 800
Toaster1100 to 1700
Electric Range (single element)2500
Hot plate1250
Electric oven5000
Personal computer500 to 2000
Vacuum700 to 1400
Table lamp150
Coffeemaker400 to 800
Television100 to 350
Hair dryer1200 to 1500
Space heater1250
Electric furnace5000 to 25000
Central air conditioning2000 to 4000
Water pump1000 to 2000
Outdoor lighting500 to 1000
Heater (radiant)1300
Water heater3000 to 4500
Water air conditioning600 to 1500
Sump pump1500

When using these appliances, check if they have a motor in them. If one has a motor, double the wattage as motor equipment draw more power than their electric counterparts. Also, if you’ll be running electronics with sensitive circuits such as TVs, phones and others, go for an inverter generator as it produces smooth and stable power that won’t damage them.