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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.

As a safety measure, you should always turn off the main breaker while operating your generator’s backup breaker. In addition, you should also switch off all appliance breakers so you don't have a power surge when the main breaker turns back on. And finally, turning off the main breaker prevents back-feeding, which endangers utility workers with the risk of electrocution. Back-feeding could also destroy the electrical circuits of your neighbors if they use the same power network.

It’s usually better to repair your generator if it isn’t working properly, as it will typically be much more affordable and should yield similar results. Generator repairs cost around $300 on average, while installing a new whole-house generator costs around $5,000 on average. The only exception is if you know your generator is reaching the end of its useful life, usually between 30 and 40 years. If you have an older generator, you could face multiple repairs in the coming years, which might mean that a full replacement will be more cost-effective over time.

Here’s what you can run with different wattages and types of generators:

Portable generator:

• 2,000 watts can handle a large appliance like a freezer or refrigerator, plus a few smaller items like phones or computer chargers. 

• 4,000 watts will keep two large appliances operating and a few smaller devices.

• 8,000 watts should power most essential appliances and other devices, including a sump pump, well pump, or your dishwasher.

Partial to whole-house generator:

• 20,000 watts and above will make it seem like your home’s power is still on.