Where should you start? Perhaps the best place is to begin by thinking about how often you will need to clean with your pressure washer. Will it be once a week or less? Then you can probably get by with one designed for residential or homeowner use. If you will need to do your cleaning several times a week, you need a unit that can handle the workload - and that may mean a commercial unit.
In your deliberations, consider just what you will be trying to clean with your new pressure washer. Will you need to clean really greasy and grimy surfaces? Then you will need a pressure washer that heats the water, as the how water is effective in cleaning grease and oil. If you can get a steam pressure washer, even better, as it will really tackle even the most greasy, grimy object.
If you need your pressure washer primarily to clean up your car or deck or sidewalk - then you will find that a unit that develops under 2000 PSI will work just fine.
On the other hand, if you are going to be cleaning things like the brickwork of your home, or a large truck, then you will need a pressure washer that develops a medium pressure of around 2000-3000 PSI.
Then there are those monsters that develop over 3000 PSI of pressure - what about them? Well, they are (as you might guess) designed for the heavy-duty cleaning you encounter in industrial and commercial environments (such as car repair shops, factories, truck depots, etc.).
If you do decide to buy a commercial-grade pressure washer, however, you will have the added advantage of a unit built from better components (especially the pump). As a result it will last longer, and it will usually come with a better manufacturer warranty.
A few final thoughts: Don't forget to ask about servicing - what will you need to do if it breaks down? In addition, make sure that you buy all the accessories you need - not all of them may be included in the kit. And please, practice safe washing procedures: wear goggles, be careful of hot water and steam, and NEVER point the stream of water at others.
