Sizing a generator is a careful process that requires calculating the electrical load of your entire house. You have to take into account every device you want to use and their wattage requirements, plus the wattage needed to start them, and look for a generator that can safely run all that at around 80% capacity.
In more practical terms, a small home can run on a 10,000-watt generator (and if you only want to power a few key appliances, much less than that). A mid-sized home may need something between 15,000 and 22,000 watts. Larger homes require 25,000 watts or more.
A home that is 2,500 square feet will likely need a 20kW to 25kW generator. Consult your local generator installer to confirm the generator size needed to power your home before purchasing a new one. Be sure to consider how much power your necessary devices need to run.
A 10,000-watt generator can run a small to mid-sized central AC unit (typically up to 3 tons or 36,000 BTU) along with a few other appliances. However, larger AC units or additional loads will require a bigger generator. Consult a local generator installer to ensure you add the correct size generator to your home.
In most municipalities, you will need a permit to install a permanent home generator, including emergency backup, partial-home, and whole-home generators. A permit for a generator usually costs between $50 and $250, depending on where you live. Your electrician or certified generator installer will usually pull the permit for you—and might be required to do so by your building department—but you’ll be on the hook for the cost of the permit. You should ask your installer before agreeing to any work if they will pull the necessary permits for your project.
To power a central air system during a power outage, the whole-house generator will need to be at least 5,000 watts, and this number will significantly increase for larger units. Check the specific wattage requirements of your AC unit to choose the right generator size. Consider consulting a generator installer to ensure your whole-house generator meets your electrical load needs.
The Karlstad, MN homeowners’ guide to generator installs
From average costs to expert advice, get all the answers you need to get your job done.
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