To simply clear a deck, a tension washer with a PSI selection of 2500 to 3000 is right

https://mega-wiki.win/index.php/Understanding_Pressure_Washer_Efficiency:_How_Many_Gallons_Per_Minute_Do_You_Really_Need%3F

To effectively clean a deck, a drive washing machine with a PSI differ of 2500 to 3000 is good. This drive stage correctly removes grime, dirt, and mildew with no negative the timber