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