Generator Buying Guide
Illustration: Consumer Reports Illustration: Consumer Reports
How Do I Calculate the Size of the Generator I Need?
Choosing the right home generator means figuring out what size you need first. Generators are sold by power output, measured in watts. The amount of power a generator delivers determines how many electronics and appliances you can run at once. A typical home needs around 5,000 watts to run several major appliances and window air conditioners. But you’ll likely need more to power a whole heating/cooling system or high-demand heating appliances like electric dryers or ovens.
Before you look through our generator ratings for the best generator for your home, make a list of the devices you’ll need when the power’s out. Then add up wattages to get you in the right ballpark.
Here are some rough wattage estimates for common essentials as you build out your list:
- Refrigerator: 300 to 800 watts
- Sump pump: 750 to 1,500 watts
- Space heater: 1,500 watts
- Window air conditioner: 1,000 watts
- Lights: 5 to 80 watts (per bulb)
- Computer: 60 to 300 watts
Types of Generators
When buying a generator, you have four options to consider: home standby generators, portable generators, inverter generators, and portable power stations.
Home Standby Generators
Home standby generators, or whole-house generators, are installed permanently on your property. They can run on natural gas or propane and kick in automatically during an outage.
• They’re by far the most expensive and should be installed by an experienced electrician who can help with town or municipal permits, noise restrictions, and proper location. Installation usually costs more than the generator itself, sometimes several times more.
• Home standby generators start automatically when the power goes out, and they typically supply more power than the other three options.
• Many units turn on automatically for a few minutes every day so that you know they’re ready to run when there’s an outage. They also run a self-diagnosis to let you know when maintenance is needed. Some even alert you or your dealer via email or text.
• You have your choice of fuel—propane, which is less risky to store than the gasoline required for other models here, or natural gas, which provides an unlimited supply of power.
• Whole-house generators, like portable generators, can pose a risk of carbon monoxide poisoning. Make sure to have working CO detectors in your home.
Typical power output:
Roughly 5,000 to 20,000 watts, but because there’s little difference in the installation costs between a smaller unit and a larger one, it makes sense to get one that can easily power your home both now and in the future.
Typical cost:
$3,500 to $7,000 without installation, which can more than double the cost.
Portable Generators
Portable generators can be moved around. Some are smaller for transporting to a tailgate, while others are better kept on your property as a backup power source.
• These units tend to cost less than home standby generators, and there’s no installation expense unless you’re connecting one to your home’s electrical box.
• Portable generators typically run on gasoline that you may need to store in large quantities. If you’re storing the unit for any length of time, you need to add a stabilizer to your gas to keep it from clogging the fuel system, which is why some units won’t start after sitting in a garage for months or longer.
• A few models run on both gasoline and liquid propane. Running a generator on propane has the added benefit of being cleaner, so fuel residue doesn’t clog up your generator’s carburetor.
• You can use portable generators anywhere on or off your property—but never in an enclosed space. Like a car engine, these models can quickly produce deadly levels of carbon monoxide. Always run a portable generator at least 20 feet from your house and equipment such as a central air conditioner condenser or a window AC, and direct the exhaust away from the house or any other structure, including your neighbors’ homes.
• If it’s raining, shield your generator with a canopy designed for your particular model.
• Some models offer electric starting. The battery required for electric start, however, might not be included.
Typical power output:
Models we test provide 3,000 to 8,500 watts.
Typical cost:
$400 to $2,000.
Inverter Generators
Like portable generators, inverter generators can be moved around. They’re much quieter because they throttle up and down to match demand rather than running at full power all the time. They also have more sophisticated exhaust systems that help tamp down noise. But inverter generators generally cost more than portable generators with a comparable output.
• Inverter generators operate more efficiently, so you can get a much longer run time from the same amount of gasoline. They also produce fewer emissions than portable generators, but you should still follow the same safety precautions to prevent carbon monoxide poisoning.
• Sizes vary widely, from large inverter generators that can power an entire house, generating 5,000 watts or more and exceeding 250 pounds, to small versions that can be taken on a camping trip, weighing as little as 30 pounds.
Typical power output:
Models we test provide 900 to 7,600 watts.
Typical cost:
$300 to $5,000.
Portable Power Stations
Portable power stations are large, rechargeable lithium-ion batteries that store electricity for when you need it. They have limitations, but they’re the only option for someone who lives in an apartment and can’t safely run a generator outdoors.
• You charge it by plugging the unit into an electrical outlet or using an included solar panel (though it will charge very slowly via the panel).
• As with a small inverter generator, a portable power station is best for shorter outages (hours, not days), and it can be great for a camping trip or tailgate. The units don’t provide as much power for as long as a portable generator and must be periodically recharged. Accompanying solar panels can help extend the battery’s run time.
• Because they have no engine, the devices are extremely quiet. They don’t produce fuel emissions or carbon monoxide, so you can use them indoors. And there are no problems with starting them because there’s nothing to start. Think of them as a giant version of the battery pack you use to charge your cell phone on the go. But they tend to be heavier and significantly more expensive than a comparably sized generator.
Typical power output:
Models we test provide 1,500 to 3,600 watts.
Typical cost:
$500 to $2500.
Generator Features to Consider
Don’t let rain, snow, or wind keep you in the dark. Look for these options to get a generator that’s as safe as possible, reliable, and tailored to your power needs.
Automatic CO Shutoff
This critical safety feature automatically shuts down a generator’s engine if a built-in CO sensor detects that the deadly gas has reached certain levels. We have over a dozen generators in our ratings with a CO safety shutoff. (CR only recommends portable generators with this feature.)
From Generac to Honda, more brands than ever offer options with this technology. You might see them advertised with marketing terms like “CO Guard” or “CO Protect.” But the only way to verify whether a generator meets one of the two standards is to look for one of these certifications on the packaging:
• ANSI/UL2201 Certified for Carbon Monoxide Safety
• ANSI/PGMA G300 Certified Safety & Performance
Low-CO Engine
Brands including Ryobi and Echo are using a low-CO engine to guard against carbon monoxide poisoning.
Automatic Start
When the power goes off, the generator automatically starts without you lifting a finger. This is great if you travel a lot or work far from home and can’t always get there quickly in an emergency.
Electric Start
Several portable models offer electric start, a push-button alternative to the hassle of pull-starting the engine. If the battery isn’t included, make sure you factor in the added cost (around $50). Stationary models have automatic starting.
Alternative Fuel Capacity
Some portable generators come equipped to run on a propane tank or a natural gas line, and others can be converted with kits.
Fuel Gauge
You might appreciate being able to check a fuel gauge to see how much fuel is left in your portable generator, especially during blackouts.
Low-Oil Shutoff
If oil falls below minimum levels, the generator shuts down to prevent engine damage. While this feature is standard for stationary generators, it’s increasingly common on portables.
Multiple Outlets
Four or more outlets on a portable generator let you use its power more effectively by spreading the load, though we recommend using them for only a few devices at home or when you’re away—say, at a campsite. See the next section on transfer switches.
Removable Console
A removable console connects to the generator, allowing you to plug in appliances without running (potentially risky) extension cords outdoors.
What’s a Transfer Switch and Do I Need One?
A transfer switch is infinitely more convenient than an extension cord and allows you to safely connect a home standby or portable generator to your circuit panel with a single cable. You won’t need to worry about overloading extension cords, which could lead to overheating and fires.
Using a transfer switch also means you can power essentials without a plug (overhead lights, well pumps, and water heaters, for example).
Here are a few important notes on transfer switches:
- We recommend that you have a licensed electrician install your transfer switch. The average cost to install one is about $1,450, according to Angi. The electrician can also walk you through the process of turning your switch on and off.
- With whole-house generators, the transfer switch turns on and off automatically when the power shuts off or goes on, respectively. For portable models, you’ll need to flip a few switches by hand when the power goes out and switch them back to bring back grid power.
- Most transfer switches are designed for a 220-volt input, which means you’ll need a generator of 5,000 watts or more.
- You’ll need to choose which circuits are connected to the transfer switch. To do so, get a digital circuit breaker finder to determine which outlets and appliances are controlled by each circuit breaker in your panel. Then label them accordingly so an electrician can connect the circuits for all your essentials.
If you’re looking to save money, you might be able to have an electrician install an interlock device instead. If it will work with your electrical system and meets local building codes, you’ll have to pay $50 to $150 for the interlock kit, plus $400 to $800 for labor, which is significantly less than you’d pay for a transfer switch. The kit allows your generator to power your home’s entire circuit breaker panel and prevents the generator from running once your electric service is restored. That’s important because running the generator after grid service is restored could fry your electronics and potentially shock a utility worker working near your home.
Illustration: Chris Philpot Illustration: Chris Philpot
How CR Tests Generators
To test generator performance, our engineers load each model with various essentials you might want to power during an outage, like a space heater, well pump, or window air conditioner. We make sure the generator can handle the load it’s supposed to and also see what happens when a sudden spike in voltage hits, like if the compressor in your refrigerator kicks on when the generator is already close to capacity. The best models take that in stride, while others bog down or even quit. A high-output generator that struggles with power delivery or quality might stall or trip a circuit when it’s bogged down.
We also consider how easy it is to move and use a generator, how efficiently it uses gasoline or other fuel, and how long it runs on a single tank.
To test for safety, we run each generator through a variety of scenarios designed to capture the ways in which a consumer might inadvertently misuse it. Our custom-built test chamber is equipped with calibrated carbon monoxide (CO) sensors, and we record CO levels throughout the container while a generator is running, noting how quickly each generator shuts off when levels become potentially dangerous.
Finally, to reduce the risk of carbon monoxide poisoning, many portable generators feature a built-in sensor that triggers an automatic shutoff if CO builds up to dangerous levels in an enclosed space. CR only tests portable generators with this built-in sensor. Some generators also have engines that emit less CO to begin with.
Test data from CR shows that this safety feature is likely to save lives, and we’ll only recommend portable generators that pass our expanded CO safety technology test.
Generator Brands
We test portable, inverter, home standby, and portable power station generators from brands like Briggs & Stratton and Ryobi in our labs.
