The combination of pressure and flow is what determines how fast a pressure washing project can be completed. High pressure and high flow are required in order to properly complete a job in a timely manner. This requires expensive, professional equipment. Low budget equipment will yield high pressure with low flow or low pressure with high flow, both of which will slow down the pressure washing project down.
Cleaning effectiveness may be enhanced with the addition of certain chemicals compounded specifically for power washing and the particular problem being treated (oil, grease, etc.). One reason for heating the water used for pressure washing is because hot water requires less chemicals to complete the power washing project.