Pressure washer basics

Pressure washers (also called power washers) are basically a pump (to pressurize water) that's powered by an electric motor or gasoline engine. The water flows through a wand with a nozzle at the end that controls how much the water spreads. A trigger turns the flow on and off. Pressure washers are rated by three specifications:

  • Pounds per square inch (psi): the measure of the dirt-loosening pressure (important for stain removal).
  • Gallons per minute (gpm): the measure of the water flow that washes the loosened dirt away (important for speed).
  • Cleaning units (cu): an overall estimate of cleaning power, calculated by multiplying psi by gpm.

It's tempting to compare pressure washers by their overall rating for cleaning units, but experts say the gpm rating outweighs psi in importance. This is because gpm controls how long it will take to wash away the dirt once it's loosened. High psi is useful for tough stains, but not otherwise. Also, too much pressure can damage car finishes and roughen wood. For the most flexibility, look for a pressure washer with adjustable pressure settings and interchangeable nozzles.

Experts estimate that a pressure washer with 2,000 psi and 2 gpm can clean about 5 to 7 square feet per minute, while boosting the flow rate to 3 gpm lets it clean about 8 to 10 square feet a minute. We found quite a few reviews from owners who upgraded to a more powerful pressure washer with a higher gpm, saying they've cut cleaning time in half.

When it comes to psi ratings, experts suggest erring on the side of buying a bit more power than you need, since running a pressure washer at full blast can wear it out too quickly. By comparison, a garden hose delivers about 40 psi.

  • 1,000 to 1,600 psi: good choice for washing cars, bicycles, lawn furniture and grills
  • 1,400 to 1,900 psi: appropriate for cleaning a patio or small deck
  • 2,000 to 3,000 psi: more power for cleaning a large deck or washing siding
  • 2,800 to 4,000 psi: best for cleaning stained concrete, stripping paint

Consumer-grade pressure washers use only cold water. Water that's above a certain temperature (usually around 104 degrees Fahrenheit) can damage the unit. However, experts say it takes hot water (plus detergent) to blast away grease and oil, so for this kind of job, you'll probably need to rent a hot-water pressure washer. This report covers only cold-water pressure washers appropriate for residential use.

Gas vs. electric pressure washers

Gasoline-powered pressure washers provide the most power, but the extra power comes with trade-offs. Gas pressure washers are louder, harder to start and more expensive to operate. They're also worse for the environment because of engine emissions, gasoline fumes and the possibility of spilling gasoline while refueling.

For these reasons, a number of experts recommend electric pressure washers if they'll do the jobs you handle most often. Their lower power is much safer for car and bicycle paint, and less apt to raise splinters on a wooden deck. However, electric pressure washers can only be used within about 100 feet of an outlet, and some require a 20-amp circuit. The lower price also means less durability; some experts call cheap pressure washers that use wobble or axial pumps "throwaways" because it's not cost-effective to repair them.

Best pressure washer pumps

If you plan to use a pressure washer frequently, you might consider spending more up front for a model built with more durable parts. Experts say the pump is the crucial component. Commercial-grade ceramic triplex pumps with brass heads last the longest and can be easily repaired. Ceramic or ceramic-coated plungers are also superior to aluminum plungers, especially if you have hard water (mineral buildup on aluminum can be a problem). A brass manifold is better than aluminum, and stainless-steel moving parts are also a plus.

Axial cam pumps and even cheaper wobble pumps are usually just replaced when they wear out or break. They're used on pressure washers designed for light homeowner use -- about 20 hours a year or less. They're sometimes advertised as "no-maintenance" but this really means they're not cost effective to repair.

It's indeed possible to buy electric pressure washers that are built for long-term use. Commercial models by Annovi Reverberi and Cam Spray are built with excellent pumps and much sturdier components than bargain-priced homeowner models. For frequent use, these high-end models are cost effective and they're also a more environmentally friendly option than replacing a cheap pressure washer every year or two. Sistema, a European company, makes highly rated, reasonably priced pressure washers, but they're difficult to find in the U.S.

Pressure washer buying considerations:

In addition to choosing a pump carefully, reviewers say you should consider the following factors when choosing a pressure washer:

  • Consider renting. Experts say most homeowners only use a pressure washer about 20 hours a year, often even less. If you do plan to use a pressure washer for an occasional big job, such as cleaning siding or a big deck, consider renting one instead.
  • Look for CARB-certified gas pressure washers. Models that meet California Air Resources Board (CARB) emissions requirements are less polluting and emit fewer gas fumes. Quite a few gas pressure washers use Honda engines that meet these stricter requirements. Reviewers especially recommend Honda GX OHV engines for long life and fuel efficiency; the less expensive Honda GC engines get mixed feedback. Subaru also makes CARB-certified engines; some (but not all) Briggs & Stratton engines also meet the California standards.
  • Threaded brass connections with O-rings are better than bayonet connections. We found quite a few complaints about connections leaking, so this can make a difference in your satisfaction. Owners also complain about cheap plastic threads on a number of inexpensive electric pressure washers.
  • Pneumatic tires absorb some of the vibration. They can reduce noise, ease mobility and keep the pressure washer from dancing around during use. Reviewers also like "never-flat" tires, so it's a trade-off that boils down to personal preference.
  • Not all pressure washers let you adjust the pressure. This may seem surprising, but it's an extra feature found mostly on expensive professional-grade models.
  • Separate spray tips give you more options. It sounds convenient to have one adjustable tip, but some owners say they wish they had more choices. It can also provide more security to know you've selected the proper nozzle for the task at hand -- one that won't damage what you're cleaning.
  • Electric induction motors are better than universal motors. They're quieter, more durable and run cooler, so the pump lasts about three times longer.
  • Turbo nozzles do add stain-removal power, but can leave streaks. Experts don't recommend using a turbo nozzle to wash cars, noting that too much pressure can also damage the paint. Turbo nozzles do speed cleaning for decks or grills, and experts say a turbo nozzle can clean concrete about three times faster than a regular nozzle.
  • Some electric models require a 20-amp circuit. Keep in mind that pressure washers that need a higher-amperage outlet also need a special extension cord, which can be quite expensive.
  • On most electric models, releasing the trigger cuts the motor, saving electricity and eliminating unnecessary noise, but also protecting the power washer from damage. Some manufacturers call this a "total stop trigger gun." On some electric and most gasoline models, however, you'll need to manually turn off the engine if you take a break longer than a specified number of minutes. This time varies from less than two minutes to five minutes. The longer time is clearly more convenient.
  • Check return policies as well as service and parts availability before buying. Gasoline pressure washers are especially hard to ship for service, so it's better to buy a brand that can be repaired locally. Consider the cost of accessories if you want them.
  • Check instructions and warranty fine print very carefully. Some companies honor a warranty only if the pressure washer has been bought from an authorized dealer, or if the warranty has been registered. There are also many ways to damage a pressure washer through misuse or failing to winterize it properly, which will void the warranty, so read and follow instructions with care.

Note that pressure washer warranties don't cover anything the manufacturer considers to be the owner's fault. Gas pressure washers require a lot of maintenance -- oil changes, spark-plug replacement and fuel-saver additive to keep water out of the gasoline. You may need to be careful about the grade of gasoline, too. Pumps need to be winterized with great care, or the pressure washer won't start the following spring. Our Useful Links page has more information on maintenance.

The average municipal water system provides about five gallons per minute of water, so getting enough water flow won't be a problem. If your household water draws from a well, you'll need to be sure you select a pressure washer with an appropriate gpm rate for your well. (You can check your water system's gpm rate by running water for one minute into a 5-gallon bucket.)

For gas pressure washers, find out how long you can take a break from spraying. When you release the trigger, pressure and heat build up that can start damaging the pump within minutes. Sometimes the time limit is hidden deep in the instruction manual. Unloaders are designed to minimize pressure buildup, while bypass valves or thermal relief valves are designed to cool the water (which the engine keeps heating up). Experts say some of these devices work better than others, but it's still safest to be sure to pull the trigger briefly at least once a minute to send some cool water through the pump.

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