Home standby generators keep you living comfortably when a power outage occurs. Most home standby generators are paired with automatic transfer switches which seamlessly transfer your power in seconds. In order to effectively use the generator and transfer switch you must correctly size your generator. If your generator and transfer switch are unevenly paired, your backup power supply will not function as it should.

Make Choices

In order to start the process of sizing your generator, you have to decide how much backup power you will need. Generators are measured in kilowatts, or kW's. There are smaller units, like the Kohler 12RESVL, which are designed to power select circuits. Larger home standby models, such as the Kohler 20RESA are considered whole house generators because they can typically back up your large and small electronic items.

AP Electric has provided a generator sizing tool which will help you understand how much power your household items require to start and run. To use the tool, simply select the types of electronic items in your home and the form will populate with the standard starting and running watts. For example, when you select refrigerator, the form populates 700 running watts and 2200 starting watts automatically. Using the generator sizing tool will help you to decide if powering your entire home is actually an affordable option. If powering your entire home would require 38,000 watts of power or more, you might be looking at a small liquid cooled unit, like the Kohler 38RCL. Liquid cooled generators can be used as home standby units, however they tend to be more expensive than the air cooled units. If the 38RCL or 48RCL are not options that work into your budget, you can use the tool to determine what you can power with a large air cooled unit, like the Kohler 14RESA or Kohler 20RESA.

Prioritize your Power

A list of devices you will power will help you to decide the size of generator you will need. Your list should have critical circuits needing to be powered and a second list for “convenience” circuits. Make sure to record each device’s power requirements in watts (power requirements are simple and easy to convert). 1,200 volt-amps = 1,200 watts. If only the voltage and amps are given, multiply the amps by the volts to obtain watts (120 volts x 10 amperes = 1,200 watts.) You can convert kilowatts to watts by dividing by 1,000. You should determine start-up power requirement for any appliances with electrical motors since they require more power to start than to run. You should contact the manufacturer if the appliance documentation does not provide the startup current or requirements. In order to determine the necessary kilowatts you should add up the power requirements of all the circuits required and then divide the total by 1,000 and round the result up to nearest whole number.

Choose your Generator

After you have determined your power requirements and prioritized the circuits you are going to back up finding the correct generator should be a breeze. If you have determined that you need to back up 17,000 watts of power, we recommend using a generator that can provide at least 20,000 watts if power, or a 20kW Generator. If you select a generator that has just enough power to get by you are running the risk of overloading the circuit. Consider the extra kWs breathing room for your machine.

Once you have selected your generator, you will be looking for the appropriate transfer switch. Matching your transfer switch to your generator is a vital part of the process. We recommend speaking to a customer service representative to find the best transfer switch for your application.