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Choosing a Pressure Washer


Robert M. Hinderliter, President

Rahsco Cleaning Systems of Fort Worth

2513 Warfield StreetFort WorthTX 76106

Phone: 800-433-2113, Email: rahsco@dcs1.comwww.dcs1.com , www.pressurewash.com


Commercial or Consumer Washer


There is a wide range of pressure washing equipment available from consumer’s stores like Lowe’s and Home Depot to Industrial Supply Houses to Specialty Pressure Washer Dealers.  The main difference between these sources is the support (consumer stores often do not know what they are selling or how to use it with little or delayed support) and the quality of the equipment.  Typical consumer units are designed for a 100 hour life with 20 hour annual usage.  This is a 5 year life for a typical consumer and a Dixie Cup Washer for the average contract cleaner.  Typical Commercial/Industrial Washers are designed for several thousand hours of usage.


Because of the size and growth of the consumer market manufacturers are forced into redesigning their washers for this market.  This makes it almost impossible for the contractor to distinguish between a consumer pressure washer designed for 100 hours of usage (20 hours/year for a 5 year life) and an industrial washer designed for several thousand hours of usage.  The exterior of the washers look the same and the difference being in the quality of the interior parts.  This is compounded by the fact that the flow (gpm - gallon per minute) and pressure (psi - pounds per square inch) may be identical.  Therefore, for a one time short duration job a Dixie Cup pressure washer may be a better choice than renting a commercial pressure washer.


Choosing a Vendor will depend on how important the following items are to you:  Technical Support before and after purchase, Reliability, Ease of Maintenance, Usage Requirements (one time only or every day), importance of operations, parts availability, maintenance and operational training, and entrepreneur support for starting and operating a business.


Typical consumer pressure washers have the following design parameters that are obvious to the buyer:


  • Pressure fed (garden hose hook up required) Direct Drive Pumps
  • Pull Start Gasoline Engines or 115 volt electric motors.
  • Pumps with integral pressure regulator, by-pass line, inlet regulator, and pop-off valve.  This makes maintenance and repair difficult and requires proprietary parts which often are difficult to get or unavailable in a reasonable length of time.
  • Dual Lance variable pressure wands.
  • Low Pressure Chemical Injection after the pump.
  • Pressure nozzles with plastic inserts.
  • Zero degree rotating nozzles.
  • Components that are not obvious to the buyer are single usage internal plastic and brass parts instead of stainless steel.


Typical industrial/commercial pressure washers have the following design parameters that are obvious to the buyer:


  • Belt Driven Pumps drawing water from a float tank.
  • Electric Start Gasoline Engines or 220 volt electric motors.
  • All components are separate such as: pumps, pressure regulator, by-pass line, inlet regulator, pop-off valve, and high limit switches.  This makes maintenance and repair much easier.  Defective components can be diagnosed and repaired.  Substitutions or alternative components can be used.
  • Trigger Spray Gun with interchangeable wands and nozzles.
  • High Pressure Chemical Injection with low pressure chemical injection as an option.
  • Stainless Steel or Carbide Inserted Pressure nozzles.
  • Heaters for heating the pressurized water to 200º F.  Note:  the pumps handle cold water only, heating is after the pump.
  • Components that are not obvious to the buyer are internal stainless steel and ceramic parts instead of plastic or other low grade materials.


Water the Universal Solvent


Water is called the “Universal Solvent” because it dissolves more substances than any other liquid including acids and bases.  Pressure washing enhances the cleaning ability of water by adding heat, solvents and chemicals, abrasion (a combination of pressure, spray angle, rotating nozzles and brushing), and dwell time.  With the proper application of these enhancers almost anything can be cleaned effectively.


Hot or Cold Water


The term “Hot and Cold Water Pressure Washers” refers to the temperature of the water being discharged and not the inlet water temperature.  A hot high pressure washer takes cold inlet water and heats it to 200ºF in about one minute.  This is referred to as instant hot water.  Cold Water pressure washers do not heat the water.


For commercial operations where grease, oil, or gum is involved hot water is required to be competitive.  Cold water, strong chemicals, and brushing will work on some applications but over 90% of successful contract cleaners use heat to cut chemical and labor expense.


Hot Water is a better solvent than cold water. Remember that clothes and dishes come cleaner faster and easier if they are presoaked and washed in hot water! The same is true in High Pressure Washing.


Common successful operations for cold water include deck and wood restoration, flat work cleaning where grease, oil, and gum are not involved (side walks and patios) , and vehicle washing with brushing (labor intensive).


Some cold water pressure washers can handle water heated to 140 to 160º F.  See product literature for exact temperature.  Hot water pressure washers heat the water after it has been pressurized by the pump up to a temperature of 200ºF.


When the trigger gun is off the water is bypassed back into the inlet of the pump.  This closed loop bypass will reach 200ºF in about 5 minutes and steam in about 10 minutes. Therefore, the trigger guns should not be turned off for over 2 minutes.  This applies to both hot and cold water pressure washers.


Cleaning Power (GPM, PSI, ºF, Chemicals, & Nozzle Type)


The Power Washing industry generally expresses cleaning power in “Cleaning Units per hour” which is PSI x GPM x 60 (pounds per square inch x gallons per minute x 60 minutes per hour), or as Cleaning Units which is PSI x GPM.  Either of the figures can typically be found on product literature.  These figures leave out three very important items:  chemicals, heat, and nozzle type.  These three items typically can multiply the cleaning effectiveness several times.


There is presently no standard that takes into consideration all five factors for cleaning ability of a pressure washer.  And total cleaning ability includes abrasion like brushing.


Most commercial hot water pressure washers can be used for any cleaning situation with the application determining the nozzles and chemicals used.




90% of the successful commercial operators use a flow volume of 4 gpm or more.  Below 4 gpm there is not enough water volume to clean efficiently.  While good cleaning can be done below 4 gpm the labor expense goes up drastically.  This makes these washers suitable for consumer use where time is not a factor.  Typically commercial pressure washers deliver 4 to 6 gpm.  Consumer pressure washers typically deliver 1.5 to 4 gpm.




PSI (pressure) is determined by orifice size and flow rate (gallons per minute).  The nozzle size standard is that a #4 orifice delivers 0.4 gpm at 40 psi and 4.0 gpm at 4,000 psi. And like wise for all of the other sizes.  It takes a nozzle chart to interpolate all of the other flow rates and nozzles sizes.


The Pressure that contractors use varies a great deal. With a fan nozzle there is almost no pressure (cleaning power) greater than 3 feet from the nozzle. The pressure and temperature drop rapidly with the distance from the nozzle. You can test this by placing your hand in a fan spray 3 feet from the nozzle then slowly moving your hand toward the nozzle.  Caution:  Injury can result if you move your hand too close to the nozzle.  Nozzles are designed for an effective range of 8 to 12 inches.

As a result of this rapid drop off in cleaning power a lot of contract cleaners will use 3,000 to 3,500 PSI to wash things that cannot stand that sort of pressure. They do this by varying the distance of the nozzle from the surface being washed. For less pressure they hold the nozzle back (increase distance from the surface being cleaned), and for increased pressure they hold the nozzle closer.

Larger companies will have washers that produce 4 to 8 GPM at 3,000 to 3,500 PSI, with 200 F. This much power is really needed for concrete cleaning while 1,500 to 2,000 is satisfactory for washing of vehicles.  The more debris or dirt you are moving the more important GPM is.  It takes water volume to move a lot of debris.  Extremely large amounts of debris take fire hose volume of water.

Heat has a great advantage where grease, oil and gum are concerned. A few Vent-a-hood cleaners will use 310 F steam but these are mostly operators over 50 years old who learned to do Vents when that was the only thing available. Younger Vent Cleaners (under 50 years old) will generally use 3,000 PSI at 200°F units. However, some vent cleaners use electric 1,000 PSI cold water washers hooked up to hot water (they hand scrape more). At the present time 3,000 to 3,500 PSI units are sort of the standard of the Contract Cleaner Market. A big reason for this is that there is not much price difference between 2,000 PSI and 3,000 PSI washers and there is a big difference in cleaning power.

The PSI for decks (wood) varies from 200 to 3,000 PSI. Too much pressure will cause the wood to fur. If this happens you will need to sand with fine sand paper or steel wool to knock off the furred surface. A lot of Deck Cleaners use a variable pressure wand so that they can adjust the pressure as necessary at the point of water impact. Using low pressure and letting the chemical do the work will avoid furring the deck. Hint: use the under side of the deck to test the PSI.

Nozzle Selection:

There are two selections that need to be made in choosing the proper nozzle: the nozzle orifice size and the spray angle. This is normally expressed as 25055 or 2505 where the first two digits are the spray angle and the last 2 or 3 digits is the nozzle size (three digits for nozzle ½ sizes).  The Spray Angle is the angle of the spray width and the nozzle size determines the gallons per minute at a particular pressure that a nozzle will pass. Therefore, in order to determine a nozzle size you need to know the GPM (gallons per minute) and PSI (pounds per square inch). To make this determination it is necessary to look up the information in a nozzle chart like in "The Rahsco Wats Blaster". 

By increasing the size you will reduce the PSI of your pressure washer and the flow will remain the same. If you reduce the pressure of your washer with the unloader you will decrease both the PSI and GPM and create undesirable and dangerous conditions in the heater. Knowledgeable contractors reduce the PSI of their pressure washers by increasing nozzle size in order to keep the GPM at its maximum. To make this determination it is necessary to look up the information in a nozzle chart.

Choices for spray angle for most nozzle sizes are 0, 5, 10, 15, 25, 40, and 65 degrees. 25 degrees fits the natural wash pattern of most contract cleaners. However, some contract cleaners prefer a 40 degree spray angle because they can hold the nozzle closer to the surface and obtain the same width of contact. The advantage of this is that greater impact pressure and higher temperature is delivered to the surface because the nozzle is closer to the point of contact. However, you have to learn to keep the nozzle equal distance from the surface; it’s like using a broom.  Fan spray nozzles are designed to be used at a distance of 8 to 12 inches.

A zero degree nozzle concentrates all of the cleaning power in a very small pencil lead stream with a high degree of cleaning power at the center of impact. This causes streaking similar to chicken tracks. Sometime you can see the entire track of your wand wash pattern. The zero degree rotating nozzles solve this problem. They have the power of a zero degree nozzle and the coverage of a fan nozzle and when used properly do not leave wand marks (tracers).  The zero degree nozzles rotate in a cone circular pattern at 1,000 to 2,000 rpm with a fixed or adjustable spray angle.

Because zero degree rotating nozzles concentrate the cleaning power, they are commonly used on low volume cold water pressure washers.  Also they are used in difficult cleaning situations such as vent-a-hoods, concrete cleaning, paint removal, and heavy equipment cleaning and on encrustations of carbon deposits.




There are many power washing chemicals including detergents, waxes, acids and brighteners designed for many applications.  Read the labels carefully to select the proper chemical for a particular application.


Always read the MSDS (material safety data sheet) on cleaners before you use them for safety hazards and proper disposal options.


Chemical Dilution is largely a matter of personal preference. For most Mobile Power Washing Chemical Cost will be between 3% to 5% of Gross Sales, Labor Cost will be 30% to 45% of Gross Sales, and Fuel for heat will be 2% to 4% of Gross Sales. Soap and Heat are cheaper than Labor! I.e. A slight increase in chemical and fuel heat cost will reduce your labor cost. Generally saving on chemical and fuel for heat are less than your increase in labor expense because of minimal heat and chemicals.


Gasoline & Diesel Engines, & Electric Motors


Electric motors offer the most reliable maintenance free power source.  While they are acceptable for light duty consumer use it takes 220 volts single or three phase to produce enough power for commercial use.  This means that for the Mobile Contract Cleaner gasoline engines are the preferred power source.  Diesel Engines use less fuel but are considerably more expensive.  So they are only economical in high usage applications.


Pressure Washer Mobility


The average gasoline engine skid mounted hot high pressure washer weighs in excess of 650 pounds.  This means that these units are typically mounted in Bob Tail Box Trucks, pick ups, or mounted on flat trailers or in enclosed trailers.  The advantage of trailer mounting is that the towing vehicle can be disconnected from the trailer for other uses.


Start Up Cost


Typical start up cost range from $200 for a consumer electric pressure washer to less than $10,000.00 for a commercial trailer mounted hot high pressure washer with start up accessories.


A search on the internet for mobile high pressure washer will result in over a hundred vendors.


Average Contractor Hot High Pressure Washer


         16 to 20 hp

         4 to 6 gpm

         3,000 to 3,500 psi


         Price Range: $4,000 to $8,000


Average Contractor Cold High Pressure Washer


         13 hp

         4 gpm

         Price Range: $1,000 to $3,000


Adding Pressure Washing for Profit


Adding power washing services has not been optional for several types of service contractors, like carpet cleaners, window cleaners, and air duct cleaners.  They have been told by central purchasing that this service was going to have to be added as they were going to hire one contractor to provide all interior and exterior cleaning services.  Other Cleaning Service Contractors have added pressure washing services because it is a natural add-on to their present customer base for both commercial and residential services. Normally this expansion included surface concrete cleaning (flat work, like parking garages, bank drive-thrus, shopping malls, fast food restaurant drive ways and side walks including gum removal, and store front including the parking areas), wood deck cleaning, exterior building restoration, kitchen exhaust cleaning, house washing, and vehicle fleet washing. With this in mind we would like to offer some things for consideration as you plan to expand your existing business or start a new one.


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