Portable Generator Buyer’s Guide

Generators

There are four main types of generators: portable, residential, industrial, and RV.

This guide will discuss some of the things you might want to look for in a portable generator.

Portable generators are small and powerful enough to provide an energy source in remote areas or job-sites, or to act as a temporary backup during residential power outages.

Fuel

For many people, the first consideration when shopping for a portable generator is what type of fuel it requires. Generators can be powered by gasoline, diesel, propane, or natural gas. Some models allow you to switch between fuel types.

Gasoline

For most homeowners who need a generator for emergency or backup use, gasoline is the fuel of choice.

Gasoline generators tend to be more cheaply priced than other models, and most of the time fuel is readily available.

However, gasoline-powered generators need to be refueled regularly, no matter what the weather is like, and gasoline may be difficult to acquire in case of a power outage or natural disaster.

Gas-powered generators require more upkeep and care than other fuel models.

Gasoline is slightly more dangerous to store than diesel, as it has a lower flash point temperature.

Gasoline also has a relatively low shelf life, and most blends begin breaking down or absorbing moisture within a month. Even gasoline that is several years old is viable, but it may contain elements that will break down or wear engine parts. If you plan to use your generator very infrequently, consider adding fuel stabilizer or choosing a different type of fuel.

Also, be aware that major power outages also affect local gas stations, so it may be difficult to refuel. There could also be fuel shortages due to high demand in your area.

Gasoline is a more efficient fuel than propane or natural gas, but is less efficient than diesel, offering 125,000 BTUs per gallon (enough to heat an average sized room for 5 to 10 hours).

Diesel

Diesel generators require less upkeep and are more efficient than other fuel types. They are typically preferred for their efficiency and low maintenance.

Most diesel generators provide more horsepower per gallon of fuel than comparable gas-powered generators. They can also run for years without maintenance.

Although diesel generators have a reputation for being more durable than gas, if they are not run regularly they may be more prone to breaking down.

Diesel generators are more expensive than comparable gas models.

Diesel is generally safer to store than gasoline, as it requires a higher temperature to ignite.

Diesel has a longer shelf life than gasoline, lasting a few months before beginning to degrade. Like gasoline, diesel will burn even after years of storage, but it may degrade the workings of your engine.

Diesel is the most efficient of generator fuels, offering 138,700 BTUs per gallon of fuel (enough to heat an average sized room for 6 to 12 hours).

Propane

Another option for fueling your generator is propane. Sometimes called liquid petroleum gas (LPG), propane requires a tank separate from the generator. These tanks can be the same kind used for fueling heaters and grills, or you can rely on a larger, stationary tank that must be periodically refilled by a service truck.

Unlike gasoline and diesel, propane will not degrade in storage, so it is a good option for those who may rarely use their generator.

Propane is less efficient than both gasoline and diesel, offering 91,300 BTUs per gallon.

Natural gas

A final fuel option for portable generators is natural gas.

Natural gas generators require an existing gas line, or the willingness to invest in bringing a line to the area where you will need to use the generator.

One of the advantages of natural gas is that it is less likely to be unavailable due to power outages or high demand, though in case of a severe natural disaster, natural gas lines may be broken or shut down.

If you opt for a natural gas generator, make sure your gas line has the required pressure. If the required pressure of the generator is greater than what comes through the gas lines to your home, the generator may not work.

Natural gas is the least efficient of the generator fuels, offering 90,800 BTUs per gallon.

Multi-fuel Generators

There are also bi- and tri-fueled generators available. These generators can switch between different types of fuel with relative ease. These models use gasoline, natural gas, and/or propane.

Your wattage rating will drop as you switch from gasoline to propane, and drop again as you switch to natural gas, as each offers slightly less power.

Multi-fuel generators are more expensive than single-fuel models. Some multi-fuel generators allow you to switch between fuels without shutting down the generator, and some do not, so be sure you understand the features of your generator before you commit to buying it.

When determining what kind of fuel will work best for you, consider price, availability, safety, and storage.

Wattage

The amount of power your portable generator can produce is generally expressed in watts.

Although there are many areas where you can save money on generators, such as opting out of special features, the one area where you should never compromise is the power output of the generator. Less wattage certainly means less cost, but if your generator can’t run all of your basic appliances, it’s just a waste of money.

To determine the generator wattage you will need, add up the wattage requirements of the appliances and tools you need to run, and then add a safety margin so your generator never runs steadily at more than 60 percent of capacity.

Refer to our list of common wattage requirements, or acquire a watt meter to help estimate your power needs.

Most portable generators intended for emergency and temporary residential use are smaller units that range from 1,000 to 8,000 watts. Professional-grade portable generators intended for use at the jobsite range from 3,000 to over 18,000 watts.

Be aware that the wattage ratings of gas-powered generators are often inaccurate.

For this reason, as well as for practical purposes, if you have opted to purchase a gasoline-powered generator, invest in the highest wattage you can afford.

Voltage

Most generators are designed to supply power at either 120 or 240 volts. Some portable generators have the option to switch between the lower or higher voltage depending on whether you need to run small appliances or larger items like pumps, water heaters, or clothes dryers.

RPMs

The rate at which your generator engine runs is expressed in terms of revolutions per minute, or RPMs.

If you opt for a gasoline-powered generator, it is recommended to purchase one that runs at 1800 rather than 3600 RPMs. Lower RPMs translate to quieter function and a longer-lasting engine.

Some generators are able to switch between lower RPM speeds to offer energy generation and a higher RPM for special applications such as welding.

RPM rates translate directly to noise. If you have the opportunity, listen to the generator running before you purchase it, and bear in mind that a generator running without a load will be quieter than one running with a load. v

Optional Features

Although fuel type and wattage are typically set according to your basic needs, there are many other features where you can be more flexible and thus save money.

Brand Name

There are many brands of generator out there, and you’ll pay more for a well-known name.

In most cases, these brands have earned their reputation. However, if you are not relying on your generator for constant power, you can find a dependable model that isn’t made by one of the bigger manufacturers.

One of the better known of these manufacturers is Honda. While Honda has certainly earned its reputation as one of the toughest and most reliable generators on the market, the nice thing about Honda is that you don’t have to buy a Honda to get a Honda. Honda engines power several other brands of generator.

Portability

If you think you might need to move your generator, buy a model with wheels and handles, or invest in a portability kit with these features.

However, if you don’t plan to move your generator, or to move it rarely, this is an area where you can save money.

Tank Size

You can save money by purchasing a generator with a smaller fuel tank. Again, if you are not planning to use your generator often, or you do not mind having to refill it, there is no reason to spend the money for a larger tank.

However, think about the circumstances you might be facing. Refueling can become inconvenient or even dangerous in the right circumstances.

Starter

If you feel up to the task, you can save money by buying a generator with pull start rather than electric.

However, if you will be facing uncomfortable climates to get to your generator, it may be worth investing in the electric start option.

Valve Placement

Generators come in either overhead or side-valve models. OHVs are more expensive than models with side-head valves.

OHVs are favored because they start easier, run quieter, last longer, and produce fewer emissions than side-valve engines. However, if you don’t anticipate running your generator often, you can save money and opt for a side-head valve model.

Cylinder Lining

Generator cylinder linings are made of either cast iron or aluminum. This lining reduces wear and makes the engine last longer.

Aluminum sleeves are cheaper but do not last as long as cast iron.

Alternator Housing

Alternator housings for generators can be metal or plastic. Plastic is more affordable, but may warp or crack over time.

Alternator Bearings

Alternators that use ball bearings instead of needle bearings are more expensive, but last longer.

Brushes

Generators that feature brushes are cheaper than brushless models, but they do wear out and eventually need replacement.

However, brushless alternators require less maintenance and produce cleaner energy, which is essential if you plan to power sensitive electronic equipment.

Idle Control

Some generators feature a control to idle the engine when it is not being actively used. If you are not planning to use your generator on the jobsite, you can save money by eliminating this feature.

Low Oil Shutdown

If you have a large-capacity generator, it may come with a low-oil shutdown feature. This turns the generator off if the oil drops to a dangerously low level. If you don’t plan to use your generator often, you can save money by buying a model without this feature.

THD

If you do not need to power a lot of electronic equipment, you can forego a generator with low total harmonic distortion. THD should be below 6 percent for electrical circuits, microprocessors, and sensitive furnace controllers. Other equipment is not as affected by high THDs.

Hour Meter

Generators only used occasionally do not need the added expense of hour meters, though some come standard with this feature.

Location

How and where you plan to use your generator should guide the type of generator you purchase as well as the features you require.

The Jobsite

If you plan to use your generator on the jobsite, invest in a brand-name product that you can transport easily.

For work purposes, gasoline or diesel-powered generators make the most sense.

Because even small jobs require a lot of power, invest in the most wattage you can afford. Unless you have a specialty business, most of your tools should run on 120-volt connections, though be sure to check out all your tools to see if any require an upgrade to a 240 model.

RPMs are personal preference—go with 3600 if you need to save money, but 1800 if you need more durability or a quieter machine.

Unless it is relatively easy for you to transport fuel to the jobsite, think about spending the money for a generator with a larger fuel tank to avoid the hassle of refilling. Because you will be running the generator for longer periods of time, consider getting a model with a low oil shutdown.

Adding an electric starter is a matter of convenience. If you start the machine in the morning and it runs most of the day, a pull start is fine. If you need to shut down and restart multiple times, do yourself a favor and invest in electric start. Similarly, if the machine will run all day, consider a model with idle control to save on fuel as well as wear and tear. If the generator runs only periodically, this is an area where you can save money.

If your business relies on a generator being up and running, invest in an overhead valve model with cast iron cylinder sleeves, metal alternator housing, ball bearings, and brushless design. In high-demand conditions, there’s no sense in having to replace your generator every few years because parts are wearing out.

The Homestead

If your generator will be providing only occasional or emergency power, you can purchase a more affordable brand with less portability.

If you plan to use your generator at remote sites as well, opt for gasoline or diesel power. For strictly home use, any of the fuel options will work, though natural gas and propane are best used only in stationary units.

You can save some money by not investing in the largest wattage out there, but be sure that the generator can handle running all your essentials at the same time—especially things like refrigeration and heating. Most homes are going to require a 240-volt power supply as well, so don’t think you can get by with a 120 model unless you don’t want to run the water heater, range, or clothes dryer.

A lower RPM model is preferable to a higher one, unless you don’t plan to use the generator much and you can tolerate the decibels.

Tank size is flexible—it all depends on whether you want to refill the generator during use. Think about bad weather and blackouts as well as fuel storage issues.

You may want to consider making the investment in a generator with THD dampening to help protect any expensive electronics.

The choice of pull or electronic start is up to you. Again, think about the worst conditions you might face. If you have to brave high winds and blowing snow to get to your generator, an electronic start is worth it. If starting the generator just requires a leisurely stroll and a quick pull, save money with a manual pull start.

Unless you plan to use your generator for extended periods of time, you can save money by foregoing idle control. Occasional and temporary use means you can also opt for side head valve models with aluminum cylinder sleeves, though if you can afford it, go with the OHV cast iron models. The cost difference is not too great, and these options tend to pay for themselves in the long run.

Alternator options are similar. Plastic parts and needle bearings are cheaper, but you are relying on the generator to perform when traditional power supplies have failed, so think about spending a little bit more for metal housing, ball bearings, and a brushless design.

You can certainly forgo the low oil and hour meter options. As a homeowner, you should be performing regular yearly generator maintenance anyway.

The Right Generator

Your portable generator requirements will depend on where and what you need the generator for. Decide which features are most important and prioritize your list before shopping and making your purchase.

Ask friends and neighbors to share their failures and successes to give you an idea of what might work for you.

Finally, buy the largest wattage of generator you can. Though a surplus of power has seldom been a problem, not having enough power when you need it can leave you cold and in the dark.