The size of generator you need for a house depends on which appliances and circuits you want to run during an outage, how much power they draw while running, and the extra power some of them need to start. There is no single size that suits every home, so the right generator comes from a load assessment rather than a general rule.
Here is what goes into that sizing decision.
Priority Loads Versus the Whole Home
Start by deciding what matters most during an outage. Many homeowners focus on priorities such as the furnace blower, refrigerator and freezer, some lights, a few outlets, internet equipment and a sump pump if the home has one. Medical equipment that relies on electricity should be at the top of the list where it applies.
Others want most or all of the home powered, including air conditioning, an electric range or a well pump. Covering more loads requires more capacity, which affects the generator size, the transfer equipment and the cost.
Starting and Running Power
Every appliance has a running wattage, the power it uses once it is operating. Many appliances with motors or compressors, such as refrigerators, air conditioners, well pumps and sump pumps, briefly draw much more power when they start.
A generator needs enough capacity for the running load of everything that will operate together, plus enough reserve for the starting surge of the largest motor. Undersizing can cause the generator to struggle, trip or shut down when a large appliance starts.
Heating is a key consideration in Utah winters. A gas furnace usually needs only enough power for its blower and controls, while electric heat or a heat pump can add a large load.
Generator Ratings and Load Management
Generators are rated by how much power they can supply, and many list both a running rating and a higher starting or surge rating. Ratings can vary with fuel type, so compare the rating that applies to the fuel you plan to use. Altitude and temperature can also affect output, and manufacturer documentation explains how ratings apply.
Load management can help a smaller generator do more. Some systems automatically shed or delay certain loads, such as an air conditioner, so that large appliances do not all start at once. Whether that is suitable depends on the generator, the transfer equipment and your priorities.
Why a Professional Sizing Assessment Matters
An electrician can review your panel, list the equipment you want to back up, and estimate running and starting loads. That review also considers the transfer equipment the system will need and where the generator can be safely placed outdoors.
Homes in Salt Lake City and across Utah vary in heating type, appliance mix and size, so two similar-looking houses can need very different generators.
If you are planning backup power, our generator installation in Salt Lake City starts with a sizing assessment so the system matches the loads you actually need to run.