How To Buy The Right Residential Backup Generator

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A Briggs & Stratton PowerProtect DX 26-kW home standby generator.

Winter storms—especially in areas that don’t normally experience them—often cause power outages as heavy snow and ice wreak havoc on tree branches and power lines. Hurricanes, wildfires, and other natural disasters can also interrupt electricity services on a vast scale. However, a home standby generator, or residential backup generator, can have some or all of your household systems, lights, and appliances running again in minutes.

Dealers and other sellers list new and used residential standby generators for sale on PowerSystemsToday.com. It’s best to consult with a licensed electrician for help in choosing and installing the proper generator for your needs, but we’ve outlined the process here to familiarize you with the biggest considerations so you can make informed choices.

What Can A Home Backup Generator Do?

A typical residential backup unit can produce 120- and 240-volt electricity to power:

• A refrigerator 
• A freezer
• A furnace
• Air conditioning 
• Appliances
• Electronics 
• A sump pump
• Medical equipment
• Lights
• And more

This important source of reliable electrical power during an outage can:

• Keep refrigerated and frozen food from spoiling 
• Prevent pipes from freezing and bursting
• Maintain a comfortable indoor temperature in hot or cold weather
• Keep phone and device batteries charged
• Power a water heater and other electrically controlled gas appliances

What Are Home Standby Generators?

Popular in regions affected by natural disasters and extreme weather events, home standby generators typically produce enough power to sustain an entire household’s electrical needs for days or weeks. A home backup generator can start up automatically without your intervention when a power outage occurs when used with an automatic power transfer switch that connects the generator to your home’s circuit breaker panel.

This type of setup energizes each power circuit in your home, including ones connected to hardwired devices like central heating, ventilation, and air conditioning (HVAC) components. You’ll need to budget for the power transfer switch in addition to the generator, as well as professional installation for both.

As permanently installed equipment that can weigh 500 pounds or more, a residential backup generator has a vented enclosure to protect it from the weather and muffle its operating noise. A home generator is usually mounted on an outdoor slab at least 20 feet from the home, with its engine exhaust directed away from the house. This is for safety reasons, as a generator’s exhaust fumes contain carbon monoxide, which can be deadly if they enter through an open window or door and accumulate indoors. Most new residential backup generators automatically shut off if a sensor detects a buildup of carbon monoxide.

How Much Backup Power Does Your Home Need?

Visitors to PowerSystemsToday.com often ask, “How big a generator does my home need?” and “What generator size do I need for home backup?”

Whole-home generator models generally provide 16 to 25 kilowatts (16,000 to 25,000 watts) of standby power, which is typically enough to run an entire house's worth of appliances and systems for days or even weeks. However, it’s important to calculate your home’s actual power needs to ensure that you don’t buy a generator that’s too small (which would be overloaded and could damage your appliances) or grossly oversized for your needs (which would waste fuel).

You can calculate your home’s needs by adding:

• Total running watts
• The largest starting wattage
• A safety margin

To figure out how much generator you need, look at the label or serial plate on each appliance you want to run concurrently during a blackout, and total up how many running watts they consume. If you can’t find an appliance’s rated running watts figure, you can check its manufacturer’s website. (The label may be hard to locate behind a refrigerator or central air system, for instance.)

You can also look up typical appliance wattage figures posted by a generator manufacturer or dealer. We’ve included some examples in the chart below.

Appliance Running Wattage Examples

These are general examples of how many watts it takes to run typical appliances. Total up the running wattages of your appliances as found on their labels. Next, add the starting wattage of the most power-consuming device. Finally, add a 25% to 33% margin to determine how big a residential backup generator you need.

Add In Starting Wattage

Next, add in the starting watts of your single most power-hungry appliance, such as a laundry dryer or electric furnace. Every device with an electric motor, from the sump pump that keeps your lower level from flooding to the freezer chest preserving your food, has to overcome the inertia of its rotor (and everything attached to it) as it starts up. This can require four, five, or even 10 times more wattage to start the appliance than it does to keep it running. An air conditioner, for example, may draw 2,000 W to start up (starting watts or initial power drawn) but only 700 W of continuous power (running watts) to run.

If your biggest appliance’s label doesn’t list its starting wattage, you can get a rough estimate by multiplying its running wattage by four. Add this single figure to your total. This calculation assumes that when a power outage occurs and your standby generator begins to run, you follow the recommended plan to restart appliances one by one, starting with your most demanding device.

Add A Safety Margin

Finally, take your total of running watts plus starting watts and add 25% to 33% extra capacity to determine the ballpark wattage you need in a backup generator. This extra safety margin will keep your new power source from working too hard.

Ideally, a standby generator should run at 80% capacity or less to help it reach its maximum lifespan. The extra capacity can also help the generator handle contingencies such as high-wattage devices inadvertently starting up at the same time and accommodate additional appliances you may buy in the future.

Residential Backup Generator Fuel Options

Most home standby generators run on either natural gas from a utility line or propane from a tank. However, some models can switch between different types of fuel if one becomes unavailable. For example, natural gas utility service may be interrupted during an electrical outage.

• Natural gas. Convenient, continuous power supply (barring service outages); quiet; relatively clean burning.
• Propane. Clean burning, quiet, long storage life; available in large tanks with regular refueling service. 
• Gasoline. Very commonly available, but the cost can vary suddenly (especially during disasters); not very clean burning; relatively noisy operation; requires more frequent maintenance; fuel should be replaced when winter and summer blends become available; short shelf life—must be used in three to six months or stabilized with fuel additives to avoid going bad.
• Dual-fuel generators can burn either propane or natural gas.
• Tri-fuel generators can run on gasoline, propane, or natural gas.
• Diesel fuel. Larger generators only; efficient and reliable; moderate maintenance requirements; dirty burning with high emissions and particulates; fuel should be replaced when winter and summer blends become available.

Be aware of a generator’s run time, which indicates how long it can power your household’s load before its fuel tank needs to be refilled. The more power you use, the more fuel the generator will consume.

Other Types Of Generators For Home Backup Power

Temporary alternatives to a permanently installed home standby generator include (with some overlap):

• Portable generators
• Compact recreational generators
• Inverter generators

Like any generator with an internal combustion engine, portable, inverter, and compact recreational generators must be run outside and 20 feet or more from your home to avoid carbon monoxide dangers. However, they can be used temporarily to power individual appliances with a gen cord (a thick extension cord made expressly for generators) or extension cords with a suitable amperage rating. Drop cords with thicker wiring, such as 10- or 12-gauge (lower gauge numbers are thicker) cords, can handle more power over longer distances without overheating.

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A portable generator can serve as a temporary source of standby power for your home.

A portable generator, besides being useful for RV camping and tailgating, can act as a temporary source of (relatively noisy) standby power for your home. A compact recreational model will be smaller, quieter, and easier to move into position, but its lower wattage rating will limit you to running just a few essential appliances at a time.

Manufacturers of standard backup generators strive to support electronics with stable power and low total harmonic distortion (THD), such as 5%. An inverter generator with an extremely low THD of about 1.5% provides cleaner power for very sensitive electronics and home medical devices. While more expensive per watt, a large inverter can also run more quietly and use less fuel by reducing engine speed for lighter loads, something not all traditional generators can do.

Important Notes On Using Alternative Generators For Home Standby Power

Most portable, inverter, and compact recreational generators are not as weatherproof as a home standby unit. If rain or snow is likely before your area’s power is restored, you can protect these from the elements with an open-ended tent or a suspended tarp so long as they allow carbon monoxide to dissipate freely.

Also, you must start these types of generators manually. Models with higher output, such as a 240-V, 50-amp outlet, can safely connect to your home’s breaker box through an inexpensive generator interlock kit, a whole-home power transfer switch, or a partial transfer switch supporting a limited number of circuits. This can power hardwired systems such as a dishwasher or water heater. Never plug a generator’s output directly into one of your home’s power outlets.

Other Important Generator Considerations

In order to make sure that your residential backup generator is ready for top performance when you need it, follow the manufacturer’s regular maintenance schedule. Test its startup battery (a common point of failure), the generator itself, and its automatic transfer switch. Change filters and fluids on schedule or earlier in dusty conditions.

In addition to low-oil shutdown systems, home backup generators may offer remote monitoring abilities via mobile device or computer over Wi-Fi. Some models can notify you by email or text when service or maintenance is required. Other generators are designed to operate in extreme cold or heat. Many residential standby units come with 5- to 10-year limited warranties.

Note that home backup models are different from emergency generators, as they are not intended to run critical and emergency applications that require continuous power, such as fire alarms, police radio communications, and medical respirators.

Find The Right Home Standby Generator For Sale

Explore PowerSystemsToday.com to find new and used home standby generators for sale. Top manufacturers include Briggs & Stratton, Cummins, Generac, Honeywell, and Kohler. Again, most home standby generator buyers, especially first-timers, should ask a professional to help them select and install the best model for their needs.