How to choose the right backup generator for your home

Posted April 10, 2025 3:21 pm

James Dulley

Shrubs and other landscaping can be planted around the standby generator to hide it from view. Leave enough clearance around it for adequate air flow. Courtesy of Kohler

Q: I plan to install a backup generator for power outages. How do I determine what size I need? Would it make economic sense to just use one all the time?

A: Smaller portable or large whole-house emergency backup generators are becoming more popular because most home activities now require electricity. Power outages are not from just storms or accidents. During the summertime with high air-conditioning loads, there sometimes are brownouts from lack of generation capacity.

This is a whole-house sized standby generator being installed at a home. Notice the small gas engine inside the housing. Courtesy of Kohler

The cost to operate your own generator continuously would be more than your current electric rate, even when running it on relatively inexpensive natural gas. Since one typically runs for a relatively short time during power outages, the operating cost is not significant. Running one continuously would also wear it out because it is not designed for that and there are maintenance costs.

When selecting a backup generator, determine what you want to keep running during an outage. This impacts how large (output capacity) a unit you need. Having enough power for cooking, refrigeration, lighting, television, and operating a furnace blower are typical essential needs.

Electricity output from a generator is rated in KW (kilowatts). For a typical family of four, a 12-KW backup generator is adequate to power almost everything. By doing without some appliances and not trying to do use many simultaneously, a smaller, less expensive a 5- to 7- KW should keep essential appliances running.

To properly size your generator, make a list of the electric items you want to keep running. Check the wattage on the nameplate of each one. This is called the total “running wattage.” Appliances with electric motors are inductive devices so they require additional surge “startup wattage” briefly at startup. This can be as much as three times the running wattage.

A sizing rule of thumb is to total the running wattages for the appliances you need to keep running. Add the additional startup wattage for the largest appliance to get the rated power for a generator. The theory is all appliances will likely not start at the same time.

For example, the running/startup wattages respectively for several essential items are: refrigerator — 200/1200, several lights — 200/0, furnace blower — 800/2300, sump pump — 800/1300, and television — 100/0. The required size of a generator would be 200+200+800+800+100+2300=4700 watts.

The “rated power” output of any generator, from small portable to fixed whole-house, is the amount of wattage is can produce continually. The “maximum rated power” is the amount it can produce for a maximum of 30 minutes or so. Running at maximum output longer can damage the generator.

An ATS (automatic transfer switch) is mounted on the wall near the breaker panel. It switches from the utility power to generator power automatically. Courtesy of Kohler

If you select a whole-house generator which is attached to the breaker panel, definitely install an ATS (automatic transfer switch) with it. This is more convenient for you and safe for the utility company repair workers. When the ATS senses a power outage or brownout (low voltage), it disconnects your house from the electric grid and starts the generator.

Another advantage of having an ATS is it starts and runs the generator periodically just to make sure everything is functioning properly for when it is actually needed. This is called exercising the system.

Natural gas is the least expensive and cleanest fuel to power a backup generator. The small engine requires very little maintenance. Propane is also clean burning, but it is considerably more expensive than natural gas and requires a storage tank.

A diesel-powered generator requires more maintenance and a storage tank. A big advantage is if the electricity outage is very long, you can easily dump more diesel fuel into the tank to keep it running. A drawback is diesel fuel has a limited useful life.

If you want to just keep a light and TV running and food from spoiling in the refrigerator, get an uninterruptible power supply (UPS) for a computer. Use it for your computer too. Select one which has a maximum wattage greater than your refrigerator (200 watts for a new Energy Star one up to 400 watts for an old one).

It will power the refrigerator for a while before its battery runs down. Also get an emergency car battery power pack. Most have a 115-volt inverter and outlet, but may not be powerful enough for the refrigerator. Plug the UPS into car battery pack to recharge the UPS. The car battery pack can be recharged from your car battery system.

Q: I have a crawl space underneath my house. The floor above it is insulated. There are outdoor vents in the crawl space, but there is still mold on the underside of the floor lumber. Why?

A: Venting your crawl space was a good idea, but only a partial solution. You also should lay 6-mil thick plastic vapor barrier over the ground and up the crawl space walls to the top. This blocks the moisture.

To kill the mold on the joists, mix one-half to three-quarters cup of bleach to a gallon of water. Spray it on the joists. Wear safety goggles and protective clothing.

• Send questions to James Dulley, Daily Herald, 6906 Royalgreen Drive, Cincinnati, OH 45244 or visit www.dulley.com.

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