Published on May 26th, 2014 | by Grant Barnard


What Size Pressure Washer Do I Need?

Pressure Washing IndianapolisPower Washing is usually best done by the professional. Even with the right equipment, mistakes can be made damaging the surface forever. The DIYer can find our articles about power washing Here. Or if you are in the Indianapolis area from Greenwood to Fishers, Please see our Power Washing page.

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Three Factors Of A Properly Sized Pressure Washer

  • PSI – Pressure per Square Inch. The pressure is the force behind the amount of water that is coming out. The same PSI can be reached at any gallons per minute rating. So 3500 psi can be at 2.5 GPM or 10.5 GPM. Im sure you can figure out which will clean faster.
  • GPM – Also independent of PSI, Gallons Per Minute is how much water is coming out at whatever pressure. GPM is a serious concern. You will always need a certain amount of PSI to do the job and too much can be devastating. So it is better to have just enough pressure and more GPM to increase productivity.
  • HP – Horse Power is what drives the power washer pump. No matter what your pump is rated for, it wont be pushing the water with insufficient HP. Most units sold in big box stores are generally running with too little HP.

The Right PSI For The Job

The right PSI is hard to determine because some power washers actually push what they say they do and most do not. Depending on the water supply and whether pump is a direct drive pulling from a hose or a belt driven pump pulling from a tank. Also, the proper HP engine must be used to push the pump. We’ll talk about how tip sizes can change the pressure and water flow next. These Are Maximums depending on many factors. Figure most power washers to be running at 80% to 90%. 

  • Hi Strength Cement 3500 to 4500 psi
  • Normal Cement 3500 psi
  • Old Or Weak Cement 2000 to 3000 psi  Should be scrubbed with cleaner with stiff broom prior to pressure washing
  • New Pressure Treated Wood 2500 to 3000 psi
  • Hard Woods 2000 to 3200 psi
  • Softer Wood 2000 to 2800 psi
  • Vinyl Siding 2400 to 2800 psi
  • Exterior wood trim 2400 psi

How Tip Orifice Sizes Can Change The Pressure And Water Flow

Each pressure washer should have the appropriate tip size on it. NEVER run a smaller tip but running a larger tip can lower your psi and allow slightly more water through due to the lack of drag on the engine increasing the rpm. Only small increases in the tip size can make a huge difference.

Here is a tip size chart and a good explanation of  tip sizing. The table works like this…  1. Find your PSI.    2. Scan down to the rated GPM    3. Scan left to your appropriate tip size.

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About the Author

Grant Barnard started painting in 2000 and started Grants Painting in 2008. Originally doing business in northern Indiana, the business was moved to Indianapolis and Greenwood shortly after. Today the Grants Painting has blossomed into a reputable painting contracting company with an ever growing extensive website including our How To DIY Articles. Grants Painting covers all aspects of coatings and specialized in epoxy flooring, interior painting, exterior painting and cabinet painting.

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