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A 1,500 square foot home will likely need a 15kW to 20kW generator. When deciding on whole-house generator size, add up the total wattage of the devices that you’d like to continue running during a power outage. That way, you can ensure you purchase a generator that can power your necessary appliances or medical equipment during an electrical emergency.

To determine the right size generator for your house, you should calculate the total wattage of the appliances and devices you want to power during an outage. List all essential items, note their start-up wattages, and add them together.

Here are some typical wattage requirements for common appliances:

• Refrigerator: 600 watts

• Large dehumidifier: 700 watts

• Large window air conditioner: 1,400 watts

• Water heater: 3,000 to 4,500 watts

• Electric furnace: 5,000 to 25,000 watts

A 7,500-watt generator might be sufficient for essentials like a refrigerator, freezer, well pump, and lighting circuits. However, for high-demand items like a water heater or furnace, a whole-home generator is a better choice. A portable generator may be enough if you only need to power a few critical items.

While home square footage can offer a rough estimate, it is not always a reliable indicator. For reference, here are some typical generator sizes based on square footage:

• 1,000 sq ft: 6–9 kW

• 1,500 sq ft: 7–10 kW

• 2,000 sq ft: 10–14 kW

• 2,500 sq ft: 12–16 kW

• 3,000 sq ft: 16–20 kW+

For the most accurate sizing, consult a professional who can calculate your home's peak and average power consumption and recommend the optimal generator.

While diesel is relatively stable, it won’t last nearly as long as propane and you may have to replace it if it sits unused for too long. Diesel can sometimes struggle to work efficiently or start engines during especially cold weather, so it’s not the best choice for every climate. Compared to fuels like propane and natural gas, diesel generators tend to be noisier and create more exhaust, which isn’t always ideal for home use.

An undersized whole-house generator has the potential to overheat and shut down when you try to run a central AC system. This scenario can not only damage the whole-house generator, but can also trip your home’s breakers or cause electrical damage. To avoid this situation, hire a local generator installer to correctly size your whole-house generator.