What Size Generator to Run a 1,000-Square-Foot House?

Generator sizes for a 1,000-square-foot house

For a 1,000-square-foot house, a 7,500- to 10,000-watt generator can power the essentials and some comfort items. You could go as low as 5,000 watts if you only want to keep the essentials running. If you also need to run equipment that uses more power, like electric heat or a tankless water heater, you might need 15,000 watts or more.

For a 1,000-square-foot home, a larger portable generator may be enough to power everything you need during an outage. A standby generator offers the convenience of starting automatically.

Portable generators typically cost between $300 and $3,000, but you’ll pay closer to the upper end of that range for a large unit that can support your entire home. You’ll also have to add fuel and start it yourself.

A whole-house standby generator costs $10,000 to $25,000, though a smaller unit for a 1,000-square-foot home may cost less.

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Generator size based on power needs

It’s best to have a professional assess your power demands and size your generator accordingly, but you can also use the table below to estimate what output will suit you best.

Wattage for essential appliances

If you just want to power essential home circuits during outages, you can get away with a much smaller generator size and lower unit and installation costs.

The following items are usually considered essential, and in a 1,000-square-foot home, you can power all of these with a generator that’s between 5,000 and 7,500 watts.

• Lights: Incandescent bulbs consume 60 to 100 watts each, and LED bulbs consume 4 to 18 watts each. Across a 1,000-square-foot home, you’re looking at about 900 to 1,500 watts for incandescent lighting or 60 to 270 watts for LED lighting.
• Refrigerator: A refrigerator uses 60 to 300 watts during normal operation, but it can spike to about 1,200 watts when the compressor turns on.
• Well pump: Well pumps are necessary for water access if you’re on well water. A well pump uses around 1,000 watts during normal operation, with a spike up to about 3,000 watts as it kicks on.
• Some heating systems: Nonelectric heating systems that use fossil fuels to generate heat consume a small amount of power, usually under 500 watts, to run control boards and fans. Electric heating can use much more power, so whether a 7,500-watt generator is enough depends on your heating system and what else you’re running.
• Some small appliances: You may be able to run some small kitchen appliances on an essentials-only setup, but often not at the same time as you use other items. A coffee maker consumes 500 to 1,500 watts, and a microwave demands 600 to 1,700 watts.
• Medical equipment: You can run most at-home medical equipment on an essentials-only generator, but you’ll have to check the power demand, and you may need to stop using other items on backup power.

Note that you may not be able to power all of these items at once on a 5,000-watt generator, but you can allocate the load to different items as necessary to keep them usable during outages. Many generators have essential circuits that take priority over other circuits, so you can direct power to the most important items on backup power.

Starting watts vs. running watts

You need to account for both starting watts and running watts when sizing your generator. Adding up every appliance’s starting watts can lead you to buy a larger generator than you need. But if you only count running watts, your generator may not have enough power to start appliances like your refrigerator or AC.

Starting watts refers to the power draw of appliances and devices when they kick on. Items with resistive loads, like lights, microwaves and TVs, usually don’t require a surge of power, but items with inductive loads, like water pumps, AC units and refrigerators, can require two to four times their running loads when they turn on, and sometimes even more.

These starting loads, sometimes called surge loads, are necessary to overcome friction when starting a motor or moving stagnant refrigerant in HVAC lines. If you don’t have a generator that can handle your required starting watts, your device or appliance may fail to power on. In the worst-case scenario, you could damage the item or your generator.

How to account for startup surges

The best way to account for starting loads is to make sure you add the highest starting wattage requirements for items you want backed up to the cumulative running watts for things you want to power simultaneously. If you also include a buffer by sizing up your generator, your unit should be able to run everything at once while also starting your highest-demand items.

For some appliances and pieces of HVAC equipment, you can consider purchasing soft-start kits, which start the motor by gradually increasing voltage rather than demanding it all at once. This reduces strain on your generator and can even reduce the generator size you need to back up your home.

Lower your startup demand

A soft-start kit can reduce the power needed to start some appliances and HVAC equipment. That may let you use a smaller generator.

Calculating wattage for a 1,000-square-foot house

To get an idea of how much power your 1,000-square-foot house needs, you should start by calculating your actual electricity demands. You can use the following steps to estimate your power needs, then have a professional check your calculation before choosing a generator.

1. Make a list of everything you want to power in the event of an outage

Start with the items you use daily. Begin with the essentials and then go room by room to make sure everything you use is covered. Don’t forget your utilities, including HVAC equipment, water softeners, water pumps and water heaters.

2. Record the running watts for each item

For smaller items, like lighting fixtures and devices, you can look up their wattage online or use the estimates from the table below.

3. Record the starting watts for each item

Check the owner’s manual or the manufacturer’s specifications. If you can’t find starting watts listed, use the estimates in the table below. Starting watts are usually highest for items with compressors, pumps or electric motors, so pay close attention to refrigerators, freezers, pool pumps, well pumps and AC units.

4. Mark which items you’ll use at the same time

Look over your list and mark the devices and appliances that might run together during an outage. For example, you might use your lights, refrigerator and microwave at the same time.

5. Calculate how much power you’ll need

Add 20% to 30% to your estimated wattage needs to avoid running your generator at full capacity.

Add up the running watts for the items you’ll use at the same time. Then find the item with the largest difference between its starting and running watts, and add that difference to your total. For example, if a pump needs 1,000 running watts and 3,000 starting watts, add 2,000 extra watts to your total.

6. Add a buffer for safety

You should add a buffer of 20% to 30% to that baseline to avoid running your generator at max capacity. This will add to your whole-house generator installation costs, but it will help prevent damage to the unit as well as your appliances and devices.

Common appliance wattage ranges

If you can’t find details for the amount of power your desired items consume, you can use the table below to see average demands.

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