Portable Generators

Portable generator sizes and types

The main components of an electric generator include an engine that burns the fuel, plus a generator head that turns that power into electricity. Generators can burn propane (LP), natural gas, diesel fuel or even operate on solar energy, but most portable generators use gasoline. "Multi-fuel" or "dual-fuel" portable generators allow you to switch among fuel types (even to natural gas) by reconnecting the hose to a different source. You can also buy a conversion kit (*est. $160 to $400) to convert just about any portable generator into a multi-fuel or propane model.

Most portable generators build in several outlets -- at least two 120-volt outlets and often a DC outlet for charging a car battery. You can plug devices directly into the outlets -- for tailgating or other recreational use, or to run tools at a construction site. You can also use heavy-duty extension cords to bring the electricity into a building. Because generators exhaust far more carbon monoxide than an idling car, it is extremely dangerous (and in some cases lethal) to run them indoors or even in a crawl space or garage.

For more convenience, and to run a well pump or other device that doesn't plug into an outlet, you can install a transfer switch (*est. $250 and up). A transfer switch is a little circuit box next to your main breaker box, with a switch that keeps the electricity you generate from feeding back into the main power lines (which could electrocute a worker). More on transfer switches below.

Even with a transfer switch, you'll have to start the portable generator manually. Very small portable generators, along with budget models, use a recoil (rope pull) starter. More convenient models provide a push button electric start, and for some models, remote control is available as an extra option (*est. $390 to $450). For high end portable generators, many extra options are available, from legs to keep them out of the mud, to fitted covers and fold-up rain shelters. For the most basic models, though, you may need only a few heavy duty extension cords -- and some portable generators even offer one cord that ends in four outlets.

The first decision to make -- besides your budget -- is the wattage that you anticipate you'll need. Reviews recommend comparing portable generators by "rated watts," which is what the generator can produce on a steady basis. Maximum or "surge" wattage figures are useful for starting a motor or large appliance like an air conditioner -- but surge wattage doesn't give as accurate of a comparison. Some brands put the "maximum wattage" or "surge wattage" in the model name, which can be misleading. In describing portable generators in this report, we use the rated wattage.

Experts say generators last longer if used at about 75 to 80 percent of their rated wattage, so give yourself some leeway. On the other hand, since most portable generators run at full blast, burning fuel at top speed, it's expensive to buy a bigger model than you need. For the best fuel economy, use "smart-throttle" portable generators that vary the engine speed according to the load, daisy-chaining two if you need more wattage.

Portable generators fall into three rough size groups:

900 to 2,800 watts -- small enough to carry on a boat or to a campsite. Smaller sub1,600-watt generators are good for powering lighting, a coffee maker or a computer. By rotating usage you can use a 1,600- to 2,800-watt portable generator to power a microwave and refrigerator, or even an RV air conditioner.

4,000 to 8,000 watts -- enough for emergency use for an average 1,200- to 3,000-square-foot house. This is the most popular size range for household backup; at the higher end you can run a well pump or window air conditioner.

15,000 to 17,500 watts -- enough to run an all-electric home.

The wattage you need affects the best fuel to use, because big portable generators use more gasoline than you may want to store. For example, one owner reports that the well-recommended 15,000-watt Guardian 04582 (*est. $2,000) can burn 32 gallons of gasoline a day. That's more than six 5-gallon cans -- and it takes 16 gallons just to fill the tank once. It's easier to run a generator of this size on natural gas or from a big propane tank.

Conversely, the fuel you want to burn affects the wattage you need, because each portable generator produces less wattage from propane than from gasoline, and still less from natural gas. For example, the 10,500-watt NorthStar Trifuel 165939 (*est. $3,000) only produces 9,600 watts on propane, or 8,400 on natural gas. So if you plan to buy a multi-fuel portable generator or convert one to multi-fuel, be sure to allow for this.

You don't need that big of a generator though, unless you want to power everything in your house -- in which case, you might want to consider a standby generator that pops on automatically any time the main electricity goes off. These run about $5,000 on up, including installation -- but they last about twice as long as most portable generators. (See our Alternative Considerations section below for more information.)

For household backup, the simplest way to estimate the wattage you need is to look at your circuit box. See which circuits you'd definitely want left on in a power outage and add up the amps. Multiply the amps x 120 for single-pole outlets -- so each 20-amp circuit would add 2,400 watts to the total. This approach is especially useful if you plan to use a transfer switch instead of extension cords -- the only way to power equipment that doesn't plug in, such as a well pump.

For running a few essential appliances or tools, you can check the labels to find the starting and running wattage. If the label lists voltage and amps instead, just multiply the two figures together to get the wattage. Sometimes labels use codes; see the Best Research section below for more help calculating the wattage you need. That section also has links to several online charts that list typical wattages required by various devices.

Another approach is to buy what you can afford and rotate usage among essential devices as you need to. Reviews note that you can rotate appliances as frequently as you need to -- run the refrigerator for ten minutes to an hour, then run the freezer, then run the water pump, etc. You can also make substitutions for the big electricity hogs like clothes dryers and ranges, by hanging clothes to dry and using a propane camp stove for cooking. See the Alternative Considerations section for more ideas.

Best portable generators use inverter technology

Comparison reviews based on objective testing praise the top-of-the line portable generators made by Honda and Yamaha that use inverter technology for consistent voltage, plus "smart" throttles for fuel economy. (These vary the engine speed and fuel usage according to the electrical load.) Both features also make these portable generators the quietest available. At 47 to 59 decibels depending on load, you can carry on a conversation near them and legally camp in national park or in other campgrounds without bothering anyone. Subaru Robin makes portable generators with similar features and good fuel efficiency, but reviews criticize their inconvenient, messy oil changes.

All the Honda EU portable generators use smart throttles and inverter technology, as do the Yamaha generators with model names ending in "i." The Yamaha models offer a few advantages -- easier refilling, slightly better fuel efficiency and some high-end options like an hour meter / tachometer (*est. $50) that tells you exactly when to change the oil. However, reviews say the Honda EU portable generators are easier to carry, and Camping Life editors say it's also easier to change the oil and replace spark plugs on the Honda EU generators. Comparison tests give them a slight edge for power quality, too. The downside is that they are expensive.

The "smart throttles" on the Honda portable generators conserve fuel, which means longer runtimes per tank. You can also minimize refueling by feeding extra gasoline directly from an optional 6-gallon extended-run tank (*est. $110 to $130). Conversion kits (*est. $190 to $270) let you burn propane or even natural gas, and some retailers will do the installation for you.

Both brands let you daisy chain two portable generators for higher total wattage. You might have two linked together for household backup, but just need one for a tailgating party or camping trip. You spend more than you'd spend on one big generator, but get better fuel economy in the long run. Along with the extended-run gasoline tank, daisy chaining breaks a high-wattage setup into parts that are easy to move and store. Linking two 2,800-watt portable generators together would give you 5,600 watts (with 6,000 surge watts) -- plenty for most household emergencies.

Reviews say the 29-pound 900-watt Honda EU1000i (*est. $790) is the easiest portable generator to carry. Some owners say they carry one in each hand, then daisy chain them together for 1,800 watts total (and 2,000 surge watts for starting motors.) Tests at Camping Life find the less expensive Yamaha EF1000is (*est. $700) lighter but not quite as easy to carry. However, their tests find it to be slightly more fuel efficient, with an hour longer runtime per tank -- 6.6 hours compared with 5.6 for the Honda.

The next size up is the 1,600-watt Honda EU2000i (*est. $1,100). Daisy chaining two provides 3,200 watts with 4,000 surge watts. Camping Life editors say this portable generator is still quite easy to carry despite its 46-pound weight, because of the way it's shaped. The closest competing Yamaha is the 70-pound Yamaha EF2400iS (*est. $1,200) , which is rated at 2,000 watts.

Jumping to the next highest voltage brings electric starters, with the option of an extra cost remote control (*est. $390 to $450). This size is heavy to carry by hand, even by two people, so wheels are built in. Comparison tests give the electric start 2,800-watt Honda EU3000is (*est. $2,000) a slight edge for power quality over the 2,800-watt Yamaha EF3000i (*est. $1,900). However, the Yamaha "Boost Control" EF3000iSEB (*est. $2,100) can surge to 3,500 watts, which is especially useful for starting a small air conditioner.

You can convert any of the Honda EU portable generators to propane, natural gas or tri-fuel with a kit (*est. $190 to $270), and some retailers will do the conversion for you, but Yamaha makes multi-fuel portable generators. For example, the Yamaha EF30iSEB-B (*est. $2,300) is exactly like the "Boost Control" 2,800-watt Yamaha, but burns either natural gas or propane. The tri-fuel version, the Yamaha EF30iSEB-D (*est. $2,300), costs the same but can burn gasoline, as well.

Small budget portable generators

As a budget choice, the 1,600-watt McCulloch FDD210 (*est. $550) earns high marks from both editors and owners at ElectricGeneratorsDirect.com. Editors there rank it a "better" model compared with a Yamaha EF as the "best." (This retailer doesn't sell Honda models.) Even at this price, the McCulloch portable generator uses inverter technology to produce clean, consistent electricity, though we didn't find any head-to-head comparison tests to confirm it. At 59 decibels, it's only slightly louder than the 1,600-watt Honda EU2000i (*est. $1,100) discussed above, but at 54 pounds the McCulloch is heavier, yet lacks wheels.

The main differences, though, are in emissions, fuel economy and flexibility. The McCulloch generator doesn't meet California air quality standards so it can't be sold there. It does have a throttle control to adjust the engine and fuel consumption to the load, but runs through its 1.45-gallon tank in about 5 hours -- while the Honda can run for 8 hours (at full load) on its smaller 1.1-gallon tank. As noted earlier, two Honda EU generators can also be daisy chained for more flexible uses.

Most small budget portable generators, such as the Coleman Powermate Pulse generators, are much louder. They run at full blast no matter what the load, so even models with 4-cycle OHV engines aren't as fuel efficient. Since they don't use inverter technology, they produce less consistent voltage. You don't even get a low-oil shutoff to protect the engine from total ruin if the oil level gets too low. However, the Coleman Pulse portable generators do have some nice features, including two DC cigarette-lighter-type outlets. (The DC outlets on the Yamaha EF and Honda EU generators are only for emergency car-battery charges.)

The 1,800-watt Coleman Pulse 1800 (*est. $400) receives positive owner-written reviews at HomeDepot.com. We did find some major criticisms of this model's build quality in a review at Amazon.com. It's designed to be hand carried, but its 88-pound weight makes that a two-person job. Most owners say it's fine for the price, especially for household emergencies (for example, it can run a small portable heater). However, at 71 decibels, it's noisy -- too loud for camping near anyone else.

The 1,500-watt Coleman Pulse 1850 (*est. $400) is similar and at 68 pounds, a bit easier to carry. This budget portable generator also earns positive reviews from owners, not only at Home Depot but also in reviews at a ham radio forum, EHam.net. Owners say it's loud, but reliable. As with the Coleman Pulse 1800, fuel economy seems to vary from 4 to 7 hours per tank.

If you don't care about ultra-portability for recreational or jobsite use, you can find budget portable generators that provide a lot more watts for about the same price. They're built with a more open design, inside a protective tubular frame, usually with wheels. They're noisy, and may lack a fuel gauge or low-oil shutdown or both, but owners say they work well for emergency power.

The 3,550-watt Troy-Bilt 030248 (*est. $400) features six AC outlets instead of the two on the smaller portable generators discussed above, and comes with one cord. This one uses a 7-hp Intek OHV engine, and can surge up to 5,250 watts for starting motors. Troy-Bilt portable generators are built by Briggs & Stratton to be sold at Lowes. However, they can be hard to find in certain parts of the country.

The 3,000-watt Coleman Proforce PM0103000 (*est. $350) only has a surge rating of 3,750 watts, but it has automatic low-oil shutoff, something the Troy-Bilt generator lacks. A fuel gauge -- a convenience that most budget generators lack -- is also included.

The PM0103000 has lots of feedback and gets mostly enthusiastic praise from contractors, homeowners and RV owners reviewing it at NorthernTool.com. One owner does note that the voltage and line frequency varies a little bit under load (he measures it as 122-128 volts, with frequency 59 to 62Hz), but still rates the generator highly. We also saw some questions regarding the sturdiness of the frame and folding handle, but most were willing to overlook that in light of the Coleman generator's cost, features and performance.

Briggs & Stratton makes the Craftsman 30332 (*est. $600), but the similar Briggs & Stratton Elite 030348 (*est. $600) looks like a better buy because it provides surge protection. Except for that, the Briggs & Stratton 30348 is similar to the Troy-Bilt 030248. Tests of another generator in the Briggs & Stratton Elite series show that although it outperforms the Coleman for quality of electricity, the Troy-Bilt 030248 does about as well, for about $200 less. However, the Briggs & Stratton Elite 030348 is easier to find.

4,000 to 8,000-watt portable generators

As discussed earlier, you can get the most flexibility and fuel economy by daisy chaining two Honda EU2000i (*est. $1,100) or Honda EU3000i (*est. $2,000) portable generators to obtain 3,200 to 5,600 rated watts. However, if you want a portable generator only for homeowner or contractor use, the electric start 5,500-watt Honda EU6500i (*est. $4,000), which surges to 6,500 watts, falls in the most popular size range. It also includes a 240-volt outlet. At 253 pounds, it's heavy, but wheels and handles are built in.

This is one of the largest portable generators available that uses inverter and "smart throttle" technology. The Honda EU6500i runs at 52 to 60 decibels -- much quieter than most portable generators in this size range. The Honda EU6500i is the only "super-quiet" portable generator this big, and it's too new to be included in any of the comparison reviews we saw. We did find some discussion about it in various forums, but mostly by owners who already have smaller Honda EU models and are happy with them. We found only one report from a Honda EU65000i owner, who finds it finicky about fuel -- definitely requiring fuel stabilizer -- but otherwise excellent. Like other Honda EU generators, available accessories include an extra gas tank, propane or natural gas conversion kit and a remote control.

If inverter technology is beyond your budget, reviews recommend the Briggs & Stratton Elite portable generators with built-in surge protectors, fuel gauges, automatic low-oil shutdown and OHV engines with cast-iron sleeves. They come with wheels, the handles fold down for easier storage and most have the 7-gallon tanks. You can convert them to multi-fuel portable generators, but we couldn't find any remote control units that work with them.

Editors at Popular Mechanics recommend the 8,000-watt Briggs & Stratton EXL (Extended Life) 30244 (*est. $1,200), which also gets mostly satisfied reviews from owners rating it at Home Depot. It's in the Elite series, but offers high end features not found on smaller models. The electric start 15-hp Generac 410 OHV engine has full-pressure lubrication with a spin-on filter (like that found on a car). Reviews say this triples engine life (to an average of 3,000 hours) while increasing intervals between oil changes to 100 hours instead of 24. An hour meter tracks usage, and this model that can surge to a whopping 13,500 watts.

The portable generator review at Black Enterprise magazine recommends the 8,000-watt Coleman Powermate 8000 (*est. $1,200) . It only surges to 10,000 watts, but otherwise looks like a good buy -- with an 8-gallon tank, full-pressure lubrication and GFCI outlets. At the time of this report, only two owners have reviewed it at Home Depot, but both give it a perfect 5-star rating. Owners say the 15-hp Kohler OHV engine is quieter than the Briggs & Stratton and is easy to assemble.

Smaller generators in the Briggs & Stratton Elite series use engines that don't offer full pressure lubrication, but still get excellent reviews. Two reviews recommend the electric start 6200-watt Briggs & Stratton Elite 30242 (*est. $1,000), and owners give it top marks. It surges to 8,750 watts for starting motors. If you don't need electric start, the similar 5,500-watt Briggs & Stratton Elite 30241 (*est. $800) surges to 8,550 watts. This model gets enthusiastic owner-written reviews at both Amazon.com and at ElectricGeneratorsDirect.com, where editors rank it just under the electric start 30242.

Briggs & Stratton also makes portable generators sold at Sears under the Craftsman brand. They have a status monitor to show the electrical load and any needed maintenance, but some owners say it can be quite inaccurate. Most owners give the Craftsman generators enthusiastic reviews, but they lack the automatic low-oil shutdown, so you have to watch the oil level carefully.

Not all Craftsman generators are priced lower than the corresponding Briggs & Stratton Elite models, either. For example, the electric start 6,300-watt Craftsman Briggs & Stratton 030299 (*est. $1,200) is similar to the Briggs & Stratton 30242 but costs $100 more for only a bit more wattage. The Craftsman does surge to 9,100 watts, and owners say its power is reliable -- except for one who says it stopped working right after the two-year warranty expired.

The recoil-start 5,600-watt Craftsman Briggs & Stratton 030251 (*est. $730) surges to 8,600 watts. At first glance it looks like a better buy than the 5,500-watt Briggs & Stratton Elite 30241 (*est. $800) . The Craftsman 030298 (*est. $880) adds electric start. Both Craftsman generators hold two gallons less than the Briggs & Stratton, so they'll need more frequent refueling. Also, they lack low-oil shutoff. Owners reviewing them at Sears.com give them high ratings, but say they're loud.

Briggs & Stratton also makes Troy-Bilt portable generators (for Lowes) that receive good reviews, both in comparison tests and from owners. The electric start 5,000-watt Troy-Bilt 30343 (*est. $700) surges to 6,250 watts, and like the models discussed above, provides four 20-amp outlets plus one 30-amp 240-volt outlet. If you forgo the electric start, you can get slightly more wattage for the same price with the 5,550-watt Troy-Bilt 030245 (*est. $700) that surges to 8,550 watts, though that model can be hard to find.

Both these Troy-Bilt portable generators have 5-gallon tanks like the Craftsman generators, but substitute a fuel gauge for the elaborate status monitor. Still, reviews recommend them as good budget choices, producing reasonably consistent voltage.

The 5,000-watt Coleman Powermate PM0435001 (*est. $600) may be easier to find than the Troy-Bilt 30245. This Coleman portable generator provides low-oil shutoff, but no fuel gauge, and only surges to 6,250 watts. Tests show it produces less consistent voltage than the Troy-Bilt and Craftsman models, and we found some complaints about various Coleman portable generators leaking gasoline. However, the 6-gallon fuel tank is bigger than those on the Troy-Bilt and Craftsman models, and the Coleman gets enthusiastic reviews from a handful of owners posting to the Home Depot website.

Multi-fuel portable generators

As discussed above, you can buy conversion kits that adapt just about any gasoline fueled portable generator to burn propane or natural gas, or buy a Honda or Yamaha multi-fuel portable generator that uses superior inverter technology. However, the best-known multi-fuel portable generators are large models made by Northern Tool under the NorthStar brand. Experts warn that wattage ratings go down when you're burning propane or especially, natural gas -- so be sure to get a portable generator that's big enough. Since gasoline shortages often follow power outages, a multi-fuel model allows you additional options.

The NorthStar Trifuel 165938 portable generator (*est. $2,000) is rated at 6,600 watts when burning gasoline from its 6.5-gallon tank, but at 6,200 watts on propane, and only 5,200 watts on natural gas. Because of its price, professional reviews recommend it only if you need a multi-fuel model. We found only a few owner-written reviews -- at Amazon.com and at NorthernTool.com --but all are positive. One contractor says he runs it a full week on 12 to 15 gallons of gasoline. An electric start version is also available, the NorthStar 165920 (*est. $1,900) .

The electric start 10,500-watt NorthStar Trifuel 165939 (*est. $3,000) receives a perfect 5-star rating from six owners reviewing it at NorthernTool.com. It's run by a 20-hp Honda GX engine and provides seven outlets, with total output rated at 9,600 watts on propane and 8,400 on natural gas. Despite its big 10-gallon gasoline tank, owners say it's best to run this big a generator on gas.

We found only a handful of reviews for the electric start 5,500-watt Winco TriFuel 5500 (*est. $1,700), but owners say it can start a 2-hp motor. The 4.5-gallon tank burns about one gallon an hour at full load. Running on an 11-hp Honda engine, it's rated for 4,450 watts on propane and 4,005 watts on natural gas. It offers some high end features like a voltage regulator and brushless alternator, but the price doesn't include wheels or even a battery for the electric starter.

Large portable generators of over 15,000 watts

For even higher wattages -- to power an all-electric home, for example -- several reviews recommend portable generators made by Generac. The Generac Guardian 04582 (*est. $2,000) is rated for 15,000 watts, while both the Generac Guardian 04583 (*est. $2,500) and the Generac Centurion 5396 (*est. $2,400), sometimes called the Generac Centurion 17500P, are rated for 17,500 watts. The main difference between the two 17,500-watt models is that the Guardian 04583 comes equipped with a 60-amp pre-wired transfer switch with 16 circuits, making it something of a bargain. (More on transfer switches below.)

All three of these big portable generators are very heavy -- 450 to 525 pounds -- but include wheels. Not surprisingly, they're loud at about 77 decibels. They're powered by electric start V-twin Generac OHV engines built for many hours of use, with cast-iron cylinder sleeves and full-pressure lubrication. Other high end features include GFCI protection and electronic voltage regulation, plus auto-idle control for fuel economy. They meet EPA and CARB emissions standards.

With auto-idle turned on, the engine adjusts to one-fourth, one-half, three-fourths or full-load wattage. Because it limits the surge wattage that motors need for startup, experts say the latter feature is more relevant to industrial or professional users than to household backup. With this kind of wattage, these generators can power an all-electric house, but run through their 16-gallon gasoline tanks fast.

A 16-gallon tank only lasts about ten hours unless you use the idle control. For household use, you'll probably want to convert a portable generator this big to burn natural gas or propane with an optional kit (*est. $360 to $400). To take advantage of the wattage, you'll also probably want to install a transfer switch instead of using extension cords -- making the Guardian 04583 a better deal, since the transfer switch is included.

The 30-hp Generac Guardian 04582 (*est. $2,000) is rated for 15,000 watts, surges to 22,500 watts and can start a four-ton air conditioner. It provides nine outlets (including one DC), two of which are 240-volt -- one 30-amp and one 50-amp. It gets perfect 5-star ratings from 14 owners reviewing it at ElectricGeneratorsDirect.com, but mixed reviews at Amazon.com, where several owners report serious problems. Another owner says it can require some fine-tuning to run smoothly.

The similar 17,500-watt Generac Guardian 04583 (*est. $2,500) , complete with transfer switch, is powered by a 33-hp engine. It surges to 26,250 watts, and can start a five-ton air conditioner or even two four-ton units. At the time of this report, only five owners have reviewed it at HomeDepot.com, but they award it a perfect 5-star rating. Owners also give it positive reviews at ElectricGeneratorsDirect.com, though one points out that not all the unit's wattage is available through the 60-amp transfer switch. The 17,500-watt Generac Centurion 5396 (*est. $2,400) is identical except that it doesn't come with a transfer switch, so at that price, it's not as good of a deal.

Transfer switches

The simplest solution for occasional power outages is to use extension cords. However, these don't provide any way to power a well pump, furnace, ceiling lights or anything else that's connected directly to a breaker box. You need a transfer switch (*est. $250 and up) to power those during an outage. When you use the transfer switch, the circuits of your choice are transferred from your main breaker box to the transfer circuit-breaker box installed next to it. This safeguards electrical workers by keeping the electricity from your generator from feeding back to the regular electrical lines.

When you use a transfer switch with a portable generator, you still have to start the generator first. Then you can run just one cord from the generator to the transfer switch -- or for even more luxury, have a power inlet box (*est. $50 and up) installed on the outside wall. Then you can plug the generator into that. You'll still need to go outside to refuel the generator periodically and change the oil.

While we found some online directions for installing transfer switches, most experts recommend professional installation by a licensed electrician. Understandably, most localities require an inspection, too. All this adds to the cost. Some experts say transfer switches average about $500 installed. A licensed electrician should be able to install one in about an hour, but a power inlet may take one or two hours longer.

Types of fuel

Each type of portable-generator fuel has pros and cons. Multi-fuel generators offer a way to hedge your bet. You can also buy a kit to convert a regular gasoline portable generator to burn propane, natural gas or all three. If you live in a disaster-prone area, experts say these are worth considering. If you just want to keep a freezer going through rare electrical outages, a regular gasoline portable generator should do the trick.

Gasoline is easy to store in five-gallon gasoline cans -- in a shed away from the house. With fuel-saver additive carefully mixed in, gasoline has a shelf life as long as 24 months -- though it's better to use it within six. Reviews recommend storing at least 12 gallons for each day of anticipated outage -- more for a big generator. In widespread outages, gas station pumps may not work, so gasoline may be hard to replenish when you need it most. Spills and flammability pose additional problems.

Propane (LP) gas is considered safer than gasoline, but still should be stored away from the house. You'll need a slightly bigger generator, since rated wattage is a bit less when burning propane. Propane keeps well for about two years, either in portable 20- to 50-gallon tanks like those used for gas grills, or in more permanent 100- to 350-gallon tanks. Bigger tanks are better, since small 20-pound tanks last only about 4.5 hours on average. A full 250-pound tank should power a 7,000-watt portable generator for about 97 hours.

Natural gas is a good option for homes that use it anyway. It's considered the most environmentally-friendly fuel for portable generators and the supply is usually unlimited. (In a widespread disaster, though, delivery may be interrupted.) You'll need a slightly bigger generator, since wattage ratings are lowest when burning natural gas.

Diesel fuel is often used for sturdy portable generators designed for commercial use. Reviews say these are overkill for most homeowners; and in a widespread disaster, diesel fuel may be even harder to find than regular gasoline. Diesel-fueled engines are also harder to start in cold weather.

Biodiesel is a good choice environmentally, but 100-percent biodiesel fuel only stores well above 32-degrees F. Mixtures of biodiesel and regular diesel fuel store better in cold. Be sure that using biodiesel doesn't void the generator's warranty.

Solar portable generators provide very small amounts of electricity -- fine to run a power tool at a sunny construction site, but not dependable for emergency household electricity. See our Alternative Considerations section below for more information.

Important Features: Portable generators

Most portable generators now use fuel-efficient 4-cycle OHV engines that are easier to start, quieter and are better for the environment than 2-cycle engines. (If you have to mix oil into the gasoline, it's a 2-cycle engine.) The 4-cycle OHV engines last longer, too. Most new portable generators also provide circuit breakers, use electronic governors to regulate voltage and provide some weather protection for outlets and controls.

In choosing a portable generator, reviews consider these additional features important:

• Consider the "rated wattage," interpreting wattage ratings with care. Wattage ratings are tested under ideal conditions; lower temperatures and/or higher elevations will lower the amount of electricity produced. Use the "rated wattage" rather than the "maximum" or "surge" wattage in calculating what a portable generator will produce. Experts recommend allowing about a 20-percent margin. Take fuel into account when buying a multi-fuel portable generator, because they produce lower wattages on propane or natural gas.

• Where will you get repairs? Even after gasoline is drained from the tank, you may not be allowed to ship a portable generator to return it or get it repaired. Reviews suggest buying a portable generator with a major brand-name engine that most local service centers can repair.

• CARB compliance means lower emissions. Portable generator engines that meet California's Air Resources Board requirements, sometimes called "50-state compliant" models, are the most environmentally friendly. Budget portable generators may be only "49-state compliant," meaning they can't be sold in California because they pollute the air more.

• Acceptable sound levels depend on the situation. Portable generators can be as quiet as 47 decibels or as loud as 79 -- with the average about 75 decibels, about like the newest leaf blowers. For emergency use, louder models are usually acceptable, but for campgrounds, quieter portable generators are a must. The National Park Service requires sound levels no higher than 60 decibels at a distance of 50 feet.

• Engines with chrome or cast iron cylinder sleeves last longer, according to reviews, than engines with aluminum cylinder sleeves.

• Full lubrication with a spin-on oil filter prolongs engine life while reducing maintenance. For example, you may need to change the oil every 100 hours instead of every 24. Reviews say portable generator engines with this feature cost more, but last up to three times longer.

• Automatic low-oil shutdown can save the generator. Portable generators with this feature shut themselves down if the oil gets too low, so the motor isn't ruined. Less expensive models without this feature require vigilant attention.

• A fuel gauge adds convenience. When reviewing less expensive portable generators, this is one of the features owners miss most. It also reminds you to check the oil, since that should be done every time you add fuel.

• Idle control can save fuel by adjusting the engine according to smaller loads -- at one-fourth, half or three-fourths of the rated wattage. However, this also limits the wattage available for starting big motors, so you may not be able to use this feature all the time, even on the top-rated Honda and Yamaha models that use automatic "smart throttles."

• A USDA or US Forest Service approved spark arrester is especially important for portable generators used for camping, but to help prevent fires in household locations, as well.

• All metal brushless alternators are better than alternators with plastic parts and/or needle bearings. Reviews say brushless alternators provide cleaner, more consistent electricity for electronics.

• For household use, look for at least four outlets: preferably lock-on, with GFCI, plus one DC outlet. Locking outlets are safest, since a cord that pulls a bit loose from the generator can cause a fire. Safety experts recommend OSHA-approved ground-fault-circuit-interrupter (GFCI) outlets, since portable generators are often used in wet conditions (and they may be required at certain jobsites). If you have one 12-volt DC outlet, you can even use the generator to recharge your car's battery.

• The more weatherproofing, the better. Most portable generators protect the outlets and any status monitors, and can be used outdoors. Owners say it can be a shock to read the fine print in the manual that says "not for use in wet or damp conditions," and generator engines can ice up in cold weather. However, experts at Electric Generators Direct say it's fine to use portable generators out in the rain -- and even add gasoline -- it's just not very comfortable.

Our Consensus Report shows how many times products are top-ranked by reviewers included in our
All The Reviews Reviewed chart.

# of Picks	Model(With Retailer Links)	Details from Amazon.com
4	Honda EU2000i (*est. $1,100)	-
3	Honda EU3000is (*est. $2,000)	-
3	Generac Guardian 04582 (*est. $2,000)	details
3	Yamaha EF2400iS (*est. $1,200)	details
3	Honda EU1000i (*est. $790)	-
2	Briggs & Stratton EXL 30244 (*est. $1,000)	-
2	Briggs & Stratton Elite 30242 (*est. $1,000)	-
2	Briggs & Stratton 30241 (*est. $800)	details
2	Troy-Bilt 30245 (*est. $700)	-
2	Coleman Powermate PM0435001 (*est. $600)	details
1 each	Blue Max 1250w , Coleman Powermate Pulse 1800EX , Coleman Powermate Pulse 1850 , Coleman Powermate 8000 Electric Start , Coleman Proforce PM0103000 , Craftsman Briggs & Stratton Electric Start 030298, Craftsman 30250 (now 30332), Craftsman Briggs & Stratton 030251, Cummins Onan HomeSite 5500 , Makita G6100R , McCulloch FDD210 , NorthStar 165926 , Northstar Trifuel 165938 , NorthStar Trifuel 165939 , Troy-Bilt 030248, Troy-Bilt 30343, Yamaha EF30ISEBH

Portable generators at both size extremes get the most recommendations in reviews. The Honda EU and Yamaha EFi generators use "smart throttles" and inverter technology for fuel economy, quiet performance and very consistent voltage. The 15,000-watt Generac Guardian 04582 is the most recommended model in its size range. Among mid-sized portable generators, Briggs & Stratton takes the lead, with Troy-Bilt and Coleman as budget picks.

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