More power, more risk
Water pressure is typically measured in pounds per square inch (psi). Gas-powered models typically deliver 2,000 to 4200 psi of pressure compared with 1,300 to 2,000 psi for electric models. Much higher pressure allowed the top-performing gas machines to clean a grimy concrete patio three times faster than the fastest electrics. Gas models were up to 10 times faster at stripping paint off vinyl siding, a test we used to simulate tough stains.
On the downside, all of the gas models required more caution and control than the electrics to avoid splintering and etching wooden tables and other surfaces.