Losing power in cold weather can be troublesome and even deadly. That's why this is a good time to think about buying a generator. Need to know: Generators...

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Losing power in cold weather can be troublesome and even deadly. That’s why this is a good time to think about buying a generator.

Need to know: Generators come in all varieties, from gasoline-driven portable units designed to power up a few appliances at once, to permanently mounted standby generators that run on natural gas and operate an entire house.

Watts up: How can you figure out how powerful a generator (how much wattage) you’ll need? Find your appliances’ data plates, which will tell you the number of volts and amps each appliance uses. Then multiply the volts by the amps to get the wattage.

Most appliances are rated for “run wattage” and “surge wattage.” Run wattage is the electricity needed to operate an appliance continually. Surge wattage is the higher amount needed to start electric motors found in furnaces or refrigerators. Since appliances almost never start up simultaneously, you will need to factor in only the surge wattage with the largest difference between run watts and surge watts.

In other words, if you need 6,000 run watts total and your appliance with the greatest difference between run and surge is 2,000 watts, select a generator that will accommodate up to 8,000 surge watts.

Operating manual: A typical portable generator is rated at 2,400 to 7,500 watts. Most household appliances are rated at 120 volts, but some larger electric appliances are rated at 240 volts. If you want to power larger appliances as well as smaller ones, you will need a generator that is rated at 120 to 240 volts.

Be sure to ask: How does the generator work? Portable generators, which range from 7,000 to 10,000 watts, can be hooked up directly to plug-in appliances or connected to a circuit-breaker box and operated by a manual safety/transfer switch.

In direct hook-up, appliances can be plugged into the portable generator through a polarized extension cord that is at least 12 gauge and less than 100 feet long, to prevent power loss and overheating. If the generator connects right into the circuit-breaker box, the safety switch must be activated first, so it will disconnect the box from the electric company system and allow power to flow into your home’s circuitry.

Permanent standby generators, ranging from 7,000 to 12,000 watts, are hard-wired to the circuit-breaker box and automatically sense when the power supply is interrupted.

What will it cost? Portable generators range from $500 to $1,500. Permanent standby generators run $5,000 to $10,000 installed.

An ounce of prevention: Never use a generator indoors or in an attached garage. Operate it outside only, in a well-ventilated, dry area, away from air intakes to the home, and protected from direct exposure to rain and snow — preferably under a canopy, open shed or carport.