Jim's Post was referring to the necessary pressure to remove PAINT from cedar. You're simply washing and preping a surface for staining. You need to set the power such that you don't splinter or pulverize the wood. Usually, pressures between 1000 and 1500 are more than adequate. Use a fan nozzle, preferably a 15 degree nozzle, and hold the wand such that the stream is being applied at about 12" or so from the siding. Adjust the pressure up or down, or move the wand closer or further away, so that you aren't abusing the siding.