For removing dirt from vehicles and outdoor furniture, driveway oil stains, deck or siding mold, wall graffiti or building grime, pressure washers, also known as power washers, are the machines for the job.

Whether you're renting or purchasing a pressure washer for home or professional use, you’re likely to ask, what kind of pressure washer do I need? This pressure washer guide to will help you answer the question and make the best choice for your cleaning project.

What is a pressure washer and how does it work?

A pressure washer is a mechanical sprayer that uses an electric or internal combustion motor to power a high-pressure water pump. Water enters the machine at low pressure and exits the pump through a hose and out a spray nozzle under high pressure. The spray blasts away dirt and stains.

The pressure output, measured in pounds per square inch (psi), tells you the force of the spray. So what does gpm mean on a pressure washer? Gpm, or gallons per minute, tells you the flow rate of the water through the nozzle. Higher psi means more cleaning power, and higher gpm means faster cleaning.

What size pressure washer do I need?

What is a good psi for a pressure washer? That depends on the task. More power isn’t necessarily better, and higher pressure models can be harder to control. Consider the surface you are cleaning and pay for only the power you need.

When choosing a pressure washer, don’t look at psi alone. To calculate what size pressure washer you need, multiply the machine’s psi by its gpm to get a true measure of its cleaning capacity, called cleaning units or effective cleaning units (ECU.) This is a useful number for comparing models.

Light-duty tasks

For light-duty tasks such as washing a car or cleaning a barbecue grill, a pressure washer with 1,000 to 1,750 psi and 1.4 to 1.6 gpm (1,400 to 2,800 ECUs) will probably do the job.

Medium-duty tasks

To clean concrete, exterior siding or an asphalt driveway, you’ll want at least 2,000 to 2,800 psi and 2 to 3 gpm (4,000 to 8,400 ECUs).

Heavy-duty tasks

Heavy-duty tasks like stripping paint or removing graffiti require 2,800 psi or higher and a gpm of 3 to 4 (8,400+ ECUs).

Commercial-grade pressure washers, intended for regular use and built and powered accordingly, start at 3,100 psi. Machines such as this tow-behind model include automatic detergent injection and can be accessorized with extended reach wands, rotating nozzles, surface cleaners and sandblast attachments. Pneumatic tires are available for better traction on uneven terrain.

Electric vs. gas pressure washers

Pressure washers come in gas and electric models. For smaller jobs, an electric pressure washer will do the trick. These typically have about 1,000 psi to 1,500 psi, with a gpm no higher than 1.5. Quieter, lighter and cheaper than gas models and virtually maintenance free, they’re good for washing stains off outdoor furniture and cleaning vehicles and vehicle tires. Your mobility while using one is limited by the length of the power cord and the location of a power outlet. Many models can’t be used with an extension cord, so check the label or ask.

Gas pressure washers typically have upwards of 2,000 psi and 2 to 4 gpm. They’re a better choice for medium- to heavy-duty jobs such as washing concrete sidewalks, cleaning siding or removing paint and graffiti.

Cold-water vs. hot-water pressure washers

Cold water pressure washers are a great choice for eliminating mud, dirt and sand and are much cheaper and smaller than their hot-water counterparts. They rely on the sheer power of the pressurized water to remove dirt. They can be used with detergents, but they’re not the best option for cleaning oily or greasy surfaces.

Hot-water pressure washers are the ticket for larger or more difficult cleaning jobs, especially when it comes to removing oil and grease, which hot water cuts through more easily. Hot-water pressure washers clean faster and use less detergent than their cold-water counterparts. The tradeoff is that they are more expensive, they tend to have a lower psi and they’re bulkier.

How to choose the right size nozzle for a pressure washer

The smaller the nozzle opening, the more concentrated the spray. A spray that’s too concentrated can damage your surface, so choose carefully. Test the spray on a tough surface like concrete before you begin cleaning.

Pressure washers with lower psi values may come with adjustable nozzles. These allow you to adjust the spray while cleaning without changing nozzles for different jobs.

Most pressure washers with higher psi come with several nozzle tips, which follow a universal color-coding system that identifies the spray angle.

• Black nozzle: Use the black, 65-degree nozzle to spray detergent and soap onto a surface at a very low pressure before switching to a different nozzle to clean.
• White nozzle: The white nozzle’s spray spans 40 degrees, so water comes out at a low pressure. This makes it a good choice when cleaning anything fragile, such as windows.
• Green nozzle: The 25-degree green nozzle is commonly used for household cleaning tasks, such as removing dirt and mud from siding, decks or patios. If used carefully, it can be on cars or boats. Because the spray is wider than that of the red or yellow nozzle, it can quickly clean a larger surface.
• Yellow nozzle: The yellow, 15-degree nozzle produces a concentrated spray. It’s suitable for washing stains, mildew and paint off concrete but it can damage wood and softer materials.
• Red nozzle: The red nozzle has a 0-degree spray, so the water comes out highly concentrated. Use it on surfaces such as concrete and metal. The red nozzle can damage softer surfaces and peel off paint.

Another nozzle option is the rotating nozzle, which sprays in a circular motion. Some pressure washers also come with adjustable wands that let you set the spray pattern and pressure without changing the tip.

For removing dirt, grime and grease and preparing surfaces for painting, a pressure washer beats your garden hose every time, and it even saves water. Choosing the best pressure washer for your task will help you get the job done better and faster.

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