Dear Jim: It’s inconvenient when the electric goes off during storms. I want to get a generator. Is it expensive to operate a whole-house generator during outages? If not, why not always use one? – Cindy H.

Dear Cindy: Many homeowners install large whole-house emergency backup generators because most activities require electricity today. The problem is not from just storms. During the summertime with high air-conditioning loads, there sometimes also are brownout on hot afternoons.

Whenever there is an electricity outage or a brownout, a standby backup generator automatically starts producing electricity as soon as its engine gets started. The delay period is very short. It may run for several minutes to several days until the electricity power is restored.

Even using inexpensive natural gas, the cost to operate a generator is more than your current electric rate. Since it runs for a relatively short time, the operating cost is not significant. Running one continuously would wear it out because it is not designed for that and there are maintenance costs.

When selecting a whole-house backup generator, determine what “whole-house” means to you. 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 for most activities. By doing without some appliances and not trying to do use many simultaneously, you may get by with a smaller, less expensive unit.

To size your generator, make a list of the electric items you want to keep running. Check the wattage on each one and total them. Electric motors use more wattage briefly at startup, so add in a little extra. Since installing one is not a do-it-yourself project, contact an installer for sizing advice.

Definitely install an ATS (automatic transfer switch) with your generator. This is more convenient for you and safe for the utility company repair workers.