An electric one would do it, be cheaper, and no issues with an engine sitting around and having to add StaBil, etc. and generally deal with the mystery gas we have to buy today. Personally, in the fall, I remove the deck, scrape, wire brush, etc. hit with rustoleum and reinstall. However, I'm a fanatic about not cutting wet, or even damp grass to avoid the buildup.

Electric could work, but it helps to have some extra power for cleaning a deck. So shoot for one of the electric power washers over 2000 PSI

Yep electric would be the best option for this form of small job application . I agree that 1800 to 2000 psi would suffice as previously recommended !

There's also the cheap route, toss deck in back of your truck, trailer, etc. go to a carwash that has a hose and wand and blast it, hot water, good, though not PW pressure. One less "wonderful thing" to store. :-)