The cost to power wash a house is going to be determined by a few things. When you have a powerwasher are going to do it yourself? If you have your own powerwasher the cost will be minimal, because it will just me the price for the water you use. If you are wanting pay someone to do it, the price will be determined by a couple of factors. One thing that goes into determining the price is the size of your house, and how dirty it is. If you have a big two story house, it will cost more than a smaller ranch style house.