A good size for emergency backup is 5,500 watts
If you’re shopping for a portable generator—that is, one on wheels that’s not permanently connected to your home’s electrical system—a generator that supplies 5,500 watts is about the right size. This is enough to power a few critical appliances like a refrigerator, furnace, microwave, TV and some lights. Of course, you can’t run a whole-house air conditioner and an electric water heater at the same time with 5,500 watts, but a generator this size will get you by until the power comes back on. You can buy a good-quality 5,500-watt generator for about $700.
Buy a standby generator if you can afford it
Permanently installed generator
Portable generators are great in a pinch, but they’re often noisy and they require frequent refueling. They also have to be stored when not in use, and connected and started when the power goes out.
A standby generator is permanently connected to your home’s electrical system and goes on automatically when the power goes out, providing seamless power. Standby generators can run on propane or natural gas, eliminating the need to monitor the fuel. And they’re quieter.
You can buy one large enough to power everything in your house, or you can buy a smaller unit and choose the most critical circuits to power. Standby generators start at about $1,800, plus installation. (And they do need to be installed by a pro.)
The difference in cost between a portable generator and a standby unit may not be as great as you think. Remember, a portable unit requires either expensive extension cords or a transfer switch. Standby units can run on less expensive natural gas, which will save you money in the long run.
Propane is easier than gas
Easy refueling, lower maintenance
When it comes to portable generators and ease of use, liquid propane (LP) sure beats gasoline. Gasoline is a handy fuel, but it’s not without problems. Storing enough gasoline to get you through a several-day power outage requires constant vigilance. First you have to buy several 5-gallon gas containers and find a safe place to store them. Then you have to add stabilizer and ideally replace the gas after several months to make sure it’s still fresh when you need it.
Propane-powered portable generators solve these problems and more. You can store and use liquid propane (LP) indefinitely (it doesn’t go bad). Refueling is simple and safe; just replace the propane tank with a full one. And you don’t have to worry about the carburetor on your generator getting gummed up with old gasoline. Search online for “propane generators” to see what’s available.
Buy a generator you can get serviced locally
Check for parts and service in your area
You may find a great deal on a generator by shopping online. But what will you do if you can't get it serviced locally? Sometimes it's worth spending a little extra to buy from a local dealer. Parts will be available, and the dealer will be familiar with maintenance and repair procedures for your model. So before you buy a generator, make sure there’s someone nearby who can provide parts and service.
Furnaces, well pumps and electric water heaters require a transfer switch
Provide power to hardwired appliances
You can use extension cords from your portable generator to power any device with a plug, but anything that’s directly connected to your home’s wiring, including essentials like your well pump, furnace and electric water heater, requires a transfer switch.
A manual transfer switch is essentially a small circuit breaker box that you mount next to your main electrical panel. You match the capacity of the transfer switch to the wattage of your generator. Then you choose which circuits to connect to the transfer switch. The Gen Tran manual transfer switch shown here came prewired for six circuits and included the inlet box (generator connection) and the cord to connect the generator.
A transfer switch is the only safe way to connect your generator to house wiring because it requires you to disconnect the house wiring from the incoming power lines at the same time you switch to generator power. This prevents the possibility of “backfeeding” generated power into the power lines, which creates a potentially lethal hazard for power line workers.
Connecting a manual transfer switch is an advanced electrical project. An electrician should be able to complete an installation similar to the one shown here in about three hours.
Add up your watts—then add extra for motor start-up
If you’re the adventurous type, you can just go with our recommendation of a 5,500-watt generator and make the best of it. But if you really want to know what size generator you need to power everything you want, then the only way is to add up the wattage of all the lights, appliances and motors that you intend to run simultaneously.
Generator manufacturers and resellers have charts you can refer to that list the average wattage used for various appliances and motors. Or you can check the nameplates on the appliances you want to power. If wattage isn’t listed, you can derive it by multiplying volts by amps. For example, if the plate lists 2.5 amps at 120 volts, multiply the two to get 300 watts.
There’s one caveat, though. Motors require an extra surge of electricity to get started, and you have to factor this into the equation. Add up the wattage of everything you want to run. Then determine the largest motor you need to run (the furnace, for example), multiply the wattage requirement by 2 to get the approximate startup wattage required, and add this number to the total.
Buy gas cans when you buy the generator
A 5,500-watt generator will run about eight hours on 5 gallons of gasoline, so gas management is critical if you want to be prepared for an extended power outage. That may mean running your generator for shorter periods and coasting on things like refrigeration.
Having several filled 5-gallon gas cans available is prudent, but you’ll need to add stabilizer to extend the shelf life. Even then, after six months or so you should pour it into your car’s gas tank and refill the cans with fresh fuel. The generator itself should be run dry for storage or filled with stabilized fuel. That fuel should be replaced every six months as well.
You'll need heavy-duty extension cords
Check rated capacity
Remember, if you decide not to install a manual transfer switch, you'll need a lot of expensive, heavy-duty extension cords. Using undersize cords presents a fire hazard and can damage motors as well as stress your generator. To run a refrigerator, depending on how energy efficient it is and how far from the generator, you'll need at least a 12-gauge cord. A 50-ft. 12-gauge cord will set you back about $50. Multiply that by five or six and you can see that a transfer switch starts to sound like a better deal.
Don't wreck your TV with a cheap generator
Use “clean” power
Computers, TVs and many modern appliances contain sensitive electronics that can be damaged by the “dirty” power produced by less expensive generators. Inverter-type generators provide the cleanest power but are very expensive, especially in sizes large enough to power a house. But for a little extra money, you can buy generators with power conditioning that provides cleaner power. Total Harmonic Distortion (THD) is a way to measure the quality of electricity from a generator. Look for a generator with a THD of less than 5 percent to safely operate most electronics.
You can buy a quiet generator, but it'll cost more
Cheap and noisy or expensive and quiet?
One problem with portable generators is the noise that you—and your neighbors—have to put up with. You can compare decibel ratings to find quieter models, but keep in mind that there’s no industry standard, so you may be comparing apples and oranges. Standby generators are quieter, and for a stiff premium you can buy a really quiet portable generator like the 6,500-watt Honda shown here.