Power Requirements
Before buying any generator, you should determine the power requirements of your home and your most essential large electric appliances. Refrigerators, air conditioning, sump or well pumps, medical devices, electric water heaters and portable space heaters will likely have the highest power draw and be most essential during power outages.
Many generator manufacturers have online wattage calculators to help you determine what size generator is the best fit for your home. You can also calculate this number yourself by finding the wattage rating label on each of your essential appliances. Many appliances will be labeled with “starting watts” and “running watts.” The former is the power draw when the appliance first turns on, while the latter is the draw once it’s running.
If the starting watts are not listed, you can usually multiply the running watts by three. Add up the starting watts for each appliance, and multiply the total by 1.5 to create a margin of safety. A small to medium size U.S. household averages a minimum of 5,000 to 7,500 watts, so many generators are sold with 7,500 to 10,000-watt outputs.
NOTE: Some generators are listed by watt (W) and some by kilowatt (kW). A kilowatt is 1000 watts.
Trying to determine the size generator you’d need? If, for example, you wanted to power a window air conditioning unit, your immersion water heater and a microwave, you’d need a generator with a 10,000-watt output to be safe.
Size and Noise
Once you’ve figured out your power needs, the next two major considerations are the physical footprint of the generator and the amount of noise it makes. Whether you have a small yard or many acres of land, you’ll likely need the generator near your home, so the size and sound matter.
The larger generators featured on our list are approximately 30 inches by 30 inches by 48 inches, while the smaller generators are closer to 24 inches by 24 inches by 36 inches. The National Fire Protection Association (NFPA) code requires generators to be five feet or more away from openings such as doors and windows.
Smaller home generators are allowed as close as a minimum of 18 inches from an exterior wall, though you should always check local codes as they may differ from the NFPA’s standards.
With the generator placed immediately outside of your home, you should also consider the noise level, measured in decibels (dB). Most generators on our list average 60 to 70 dBs, for reference, a vacuum cleaner is typically approximately 70 to 80 dBs.
Fuel Type
Home generators can be run by a variety of different fuel types, but all the ones on our list use either liquid propane (LP), natural gas (NG) or both. Those that can use both fuel types are easily converted, without tools, to be ready to burn whichever fuel is needed.
The advantages of propane include its affordability and its “cleaner” burn, meaning it leaves little to no contamination. Some houses have a permanent propane tank, but propane is also available in smaller containers at grocery stores, hardwood stores and even gas stations.
Generators burning natural gas can be directly tied to the home’s natural gas line, allowing practically limitless fuel without having to worry about running out. The disadvantages of natural gas are that it’s less energy-efficient than propane and will therefore produce less power and that the generator remains dependent on the gas grid for backup power.
Purchase Price
Though a home generator is a long-term investment, the unit, and its components still must fit your budget. In general, models with higher kW output are higher priced.
Best Home Generator Prices
Fuel Consumption
The output of an electrical generator more or less determines the amount of fuel it will consume while operating. A 10-kW generator consumes around 100 to 120 cubic feet per hour of natural gas running at half capacity, while a 20-kW model requires between 190 and 290 cu ft/h at half load. Depending on the generator size and fuel cost, expect operating costs of between $50 and $210 per day.
Operating Temperature Range
Standby home generators operate in a broad range of air temperatures and depend on the model and manufacturer. Smaller generators, under around 20-kW, are most often air-cooled, while most models larger than that incorporate liquid cooling to maintain a constant temperature despite the outdoor air.
Most generators start and operate well in temperatures between 32F and 100F. However, in locations that experience temperatures well below freezing, a cold-weather kit, including a battery heater and an oil heater, will eliminate starting hesitation in very cold temps. Temperatures over 100F will significantly reduce the generator’s efficiency.
Warranties
Generator warranties are many and varied. The industry standard is a limited 5-year warranty, including parts and repair labor. Many manufacturers extend coverages to include an additional year or two, while extended warranties of up to ten years are often available for purchase.
Check warranties carefully to understand what’s covered and what circumstances trigger warranty service and which don’t. It’s common for manufacturers to vary the warranty lengths of components and what’s protected.