What's Your Pressure

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Finding the right pressure washer for the job isn’t as easy as it sounds. If you choose an under-powered product, the results will be disappointing. Going with an oversized unit adds inconvenience and extra cost. Not to mention, you risk damaging property.

So how does a person determine what type of pressure washer is needed? Education is the only answer. It takes an understanding of the machine, the application and the cleaning process itself to make a proper selection.


As with any learning process, it’s best to start with the basics. In the case of pressure washers, this means figuring out whether a hot- or cold-water unit is needed.

Cold pressure washers are compact and economical, and they’ll do the trick for a large number of jobs. Cold-water units are best at washing away dirt and mud.

Where cold water falls short, however, is removing grease or grime (dirt that is ingrained or clinging to a surface). A cold pressure washer may push these substances around, but it won’t produce a clean surface.

When dealing with grease, grime and oil, a hot pressure washer is a better choice. That’s because hot water actually cuts through grease, loosening it from the surface. Once the bond between the grease and the surface has been broken, it can then be washed away.

Also, remember that the performance of either a hot or cold pressure washer can be enhanced by using cleaning chemicals. There are a variety of detergents available for use with pressure washers, and using the right one can help the cleaning process go much more smoothly.


Both hot and cold pressure washers are available with electric motors or gas-powered engines. This decision is largely based on where the machine will be used. If it will be operated outdoors without adequate electrical sources nearby, then a gas-powered unit is the best bet. Otherwise, many people prefer electric motors for their cost efficiency, low maintenance and quiet operation. Keep in mind that many of the higher-powered electric pressure washers require a 230-volt, three-phase power source, which isn’t readily available in many locations.

If selecting a hot pressure washer, a person must also choose one of three options for heating the water: oil, gas or electric. The most popular choice is oil, and the machine can use diesel, fuel oil or kerosene to heat the water. These units are highly portable, and the fuels are affordable and readily available.

The next option is gas, which means the machine can burn either natural gas or LP gas. This option is typically reserved for stationary pressure washers that are hard-plumbed into the gas system of the building where they are located.

The third option is to use electricity to heat the water. Although convenient and highly portable, these units use high voltage and draw high current. Therefore, these products are recommended only if the operator has easy access to such electrical sources.


After deciding on the type of pressure washer, you must determine what specifications will best meet your needs. Pressure, volume and horsepower ratings are often misunderstood, but they play a large role in the performance of a pressure washer.

Start by considering pressure. Simply put, the purpose of pressure is to help break the bond between the contaminant and the surface being cleaned. If the pressure is too low, the bond won’t break without extra help from hot water or detergents. If the pressure is higher than what’s needed, the dirt will blow around more, and the high-pressure spray may even damage the surface. With this in mind, it’s best to find a happy medium – a pressure washer that has adequate ratings for the type of use it will experience.

Many people assume that pressure is the only important rating of a pressure washer, but that’s not true. Volume, which is stated in gallons per minute (gpm), equally affects cleaning performance. After the pressure has broken the bond between the contaminant and the surface, the contaminant must be washed away. And the greater the flow of water, the better the substance rinses off. In fact, professionals rely on high-volume units to complete their jobs quickly.

The third factor, horsepower, is useful because it determines how much pressure and volume a pressure washer can produce. For example, a 3,000-psi, 4-gpm unit requires at least an 11-horsepower gas engine to achieve those outputs. Anything less than 11 horsepower will deliver less pressure and volume than the pump’s actual rating.

Basic formulas can be used to calculate the minimum horsepower requirements of a machine. Note how electric-powered units use a different equation than gas-powered units:

Electric motor horsepower requirement: (psi x gpm)/1,460

Gas engine horsepower requirement: (psi x gpm)/1,100

Another way to look at the pressure and flow ratings is through cleaning units. This factors in both psi and gpm to help compare the cleaning power of pressure washers. To come up with this number, simply multiply the pressure and volume specifications. For instance, a 3,500-psi, 3.8-gpm machine would have 13,300 cleaning units, while a 3,000-psi, 4.5-gpm unit would have 13,500 cleaning units. In this scenario, the second unit would offer higher performance.

The guidelines for choosing a pressure washer aren’t complicated, but they’re important. That’s because your money may be wasted if you spend it on an inadequate unit that does a poor job. Even worse, you could pay way more than anticipated if you damage a surface with an oversized pressure washer. In the end, learning these guidelines will be well worth the time. And getting the job done right will be well worth the investment. APC

Daniel Leiss is president of Steam Jenny, Inc.


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