How to Calculate Generator Size for Your Home

How to Calculate Generator Size for Your Home

Chose your home generator based on the wattage of your appliances

By Kaye Morris

Hand Pointing to Generator
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A power outage is frustrating, but can also be costly if it extends for several days. Food can spoil in a matter of days and exposure to extreme heat or cold can leave household members with doctor-visit bills. If you live in an area with recurring power outages, purchasing a generator for temporary power is the best way to avoid discomfort and monetary loss. The generator size required to power your home is based on what you must keep running during an outage and not on the size of the home itself.

  • What You Need to Know
  • Use a licensed, insured and qualified electrican to install your generator.
  • Generators are rated in watts so you'll need to know how many watts it takes to run your lights or appliances. For instance, if you want to power 25 100-watt lightbulbs, you'll need at least a 2500-watt generator.
Generator Basics

Step 1:

List the items you must leave running during a power outage. Common items homeowners want operational are furnace fans, freezers, refrigerators and lights. Most homeowners also prefer to have a television operational to hear news about the weather and the status of the outage. Other items you may need or prefer operational are garage door openers, coffee makers, computers, electric blankets, electric water heaters, radios and space heaters.

Step 2:

Replace high wattage-requirement items with a lower wattage alternative. Central air conditioners, electric dryers, heat pumps and ovens are four of the highest-wattage draws in your home. Avoid using them if possible or replace them with an alternative. For example, instead of central air conditioning, place a fan in the room. Allow for usage of gas-powered items, if available in your home, since gas lines rarely go out as often as power lines. For example, if you have a gas fireplace, use it to heat a room rather than central heat.

Step 3:

Determine the wattage requirements for the items you must have operational during an outage. Wattage requirements are listed on the product documentation and often on the product's website. Kilowatt meters are also available that can measure the kilowatt usage of anything plugged into it. Also, companies that sell generators often make kilowatt calculators available on their websites so that homeowners can select the items they need to power and get a rough estimate of the kilowatt usage. You'll need to know both the startup and running power requirements of appliances that run on induction motors, such as freezers or air conditioners, as startup takes more power than running.

Step 4:

Select the size generator necessary to power your home based on total estimated kilowatt usage during an outage. Average homes can usually run necessary items on 7,000 watts or less. On the high end of the scale, a generator could maintain a large home at normal electric consumption with 18,000 watts. Select a generator that produces more than your minimum amount calculated.

  • Tips & Warnings
  • You won't want to run your generator at full capacity for a long period of time so a good rule of thumb is to assume it will run at 80 per cent of its rated watts.
  • If you're going to power your house on a generator and utility power at the same time, you're required to install a transfer switch that isolates the two types of power.

About the Author

Kaye Morris has 20 years of real estate development experience and is a regular contributor to DexKnows.

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