The short answer
Both use high-pressure water. Strictly speaking, power washing uses heated water, and pressure washing uses unheated water. In everyday use, most homeowners and many contractors use the two terms for the same service.
When hot water helps
Heat breaks down grease and oil faster than cold water. That is why hot water is useful on restaurant dumpster pads, drive-thru lanes, garage floors and driveways with heavy oil drips.
On most residential concrete in Los Angeles, the right detergent and enough dwell time do most of the work. Heat is a tool for specific jobs, not a requirement for every job.
When neither is the right tool
Stucco, painted siding, roofs and wood should not be blasted at high pressure. Those surfaces need soft washing: low pressure plus a cleaning solution that does the work. Too much pressure can etch stucco, scar wood and force water behind siding.
What actually determines the result
Pressure alone is not the whole story. Results come from four things working together: the right pressure for the surface, the right cleaning solution, enough time for it to work, and even coverage. On flat concrete, a rotary surface cleaner gives far more consistent results than a hand wand.
What to ask a contractor
Instead of asking whether they pressure wash or power wash, ask what they will use on each surface. A good answer names a method per surface: surface cleaner for concrete, soft wash for stucco and roofs, low pressure for wood, and degreaser for oil.
Key points
The short answer
Both use high-pressure water. Strictly speaking, power washing uses heated water, and pressure washing uses unheated water. In everyday use, most homeowners and many contractors use the two terms for the same service.
When neither is the right tool
Stucco, painted siding, roofs and wood should not be blasted at high pressure. Those surfaces need soft washing: low pressure plus a cleaning solution that does the work. Too much pressure can etch stucco, scar wood and force water behind siding.