Determining the size you need for a backup generator can be somewhat confusing. At AP Electric we pride ourselves on being able to help you through this process. There are several things that are important when it comes backup generators and their kilowatt (kW) rating. In some cases, the kW rating changes based on the fuel type. If the unit you choose runs on natural gas it will produce slightly less power than if it were operating on liquid propane. Something that can really effect the installation is whether your generator is a single phase unit, or a three phase unit. Your average home will only require a single phase unit. If you are looking for a generator for a special residential situation or for your business then you definitely want to ask an electrician which application you have.
It's standard in the generator industry that the power of a backup generator is measured in wattage. To try and make it easier it's usually represented in kilowatts or kW for short. For example a 16,000 watt backup generator will be labeled as a 16kW. Most air cooled generators are between 6kW and 22kw. The liquid cooled rating start at 22kW and can go to 560kW. Some manufacturers split the line of air cooled and liquid cooled between residential and commercial. The liquid cooled units are capable of powering more than the smaller air cooled units, so, you are more likely to find them on larger commercial properties.
Every single home with electrical appliances will have a data sticker where you can find the voltage information. This information will more than likely be listed in amps. There is an equation to help you convert your amps into watts.
Amperage x Voltage = Wattage
So, lets say that you have a twenty amp circuit and it's rated for one hundred and twenty volts. You would take 20A x 120V = 2400W or 2.4kW.
However, this only applies to single phase applications. For three phase applications you would need to contact an electrician or generator supplier. Using this equation you can add the total usage of the appliances for your entire home and determine what kilowatt size generator you would need. If you are only interested in backing up the essentials then you would only need the amps from those appliances. We've added a convenient sizing calculator to our website just in case you aren't sure of the amperage information for your home. All you have to do is select the values that would be accurate for your home and it calculates the starting and running watts for standard electrical appliances.
Like any good rule, there are some exceptions. We recommend that after you use the backup generator sizing tool on our website you confirm the total kWs with an electrician or customer service representative in our office.