Match the generator and its wattage to the appliances you plan to power

Even a small generator can power several plug-in appliances. But you'll need a larger one and a transfer switch (about $600 installed) to power furnace fans and other devices hardwired to your home. Here are some typical appliances you can power at each size level. Once you know what you're powering, total the running wattages and choose a model with a rated wattage at least equal to that total. Manufacturers suggest totaling the higher, surge watts that motorized appliances draw when you first turn them on. Based on our tests, we suggest concentrating on running watts alone.

Small portable

3,000 to 4,000 watts

What it powers:

The basics, including items such as:

• Refrigerator (600 w)
• Several lights (400 w)
• Sump pump (600 w)
• TV (350 w)
• Microwave (1,500 w)

Price range:

$400 to $800 for most; more for inverter models.

Midsized portable

4,500 to 7,000 watts

What it powers:

Same as small, plus:

• Portable heater (1,300 w) or window air conditioner (1,000 w)
• Computer (250 w)
• More lights (400 w)

Or, with a transfer switch, about $600:

• Furnace fan (500 w)
• Water pump (400 w)

Price range:

$500 to $1,000 for most.

Large portable

10,000 watts

What it powers:

Same as midized, plus:

• Water heater (3,000 w)
• Or central air conditioning (5,000 w) or range (4,500 w)
• More lights (400 w)

Price range:

$2,000 to $3,000.

Stationary unit

10,000 to 15,000 watts

What it powers:

Same as large, plus:

• Washer (400 w)
• Dryer (4,800 w)

Price range:

$5,000 to $10,000 or more, plus installation.

Watts: What Powers What

Here's a list of household items that can make blackouts more bearable, along with their typical running watts. Once you know the items you want to power, total their running watts and choose a generator with a rated wattage at least equal to that total. Manufacturers also suggest totaling the higher, surge watts that refrigerators and other motorized appliances draw when you first turn them on. That can make you buy more generator than you need; all the models we tested account for surge and handled the momentary turn-on surge without a problem. We suggest totaling running watts alone.