Pressure washers are kind of like welders. If you're starting to learn to weld, the worst thing you can do is buy a cheap welder. You'll never learn to weld well because your skills will outpace the crappy welder and you'll be upgrading. Electric pressure washers are much like the cheap welder. If you're just tacking a craft together for some windchimes or a lawn ornament, great. If you're building a tube-frame chassis, not so much.
An electric will work fine for most things, but the key part is pressure and flow. You can get a super-inexpensive 2000 psi electric and think that the price point makes it more attractive than the 2500 psi gas. Plus, it's the size of a briefcase, what's not to love, right? But when it comes down to brass tacks, the 2500 psi gas might be able to do all of your siding in 2 hours and look great, while the 2000 psi electric might take a day and a half and look like you drew lines in the stains with your finger because you had to get really close for it to be effective with its lower GPM. It's like tyring to paint a car with rattle cans vs an HVLP gun. They both get the job done, but one takes hours and has streaks, the other is even and takes 30 minutes.
That's an exaggeration, but there really is a difference. They DO make really good quality electric pressure washers, but they're about $1500 compared to a slightly better-performing $350 gas unit.
If you think about it, to get 3000-ish PSI and 2.5gpm, you need about a 6.5hp gas engine, which is about 4800 watts, or about 40-45 amps at 120v. Of course, electric is a bit more efficient, but there is just no way a 10-amp, 120v electric will compare to even the smallest gas unit. What it really boils down to is what you intend to do with it, and how long you want it to last. We used to rent high-end electric washers at HD. They cost us $1800 each to purchase, and they were completely outgunned in performance by any of the $250 gas washers on the shelf for sale. The main difference was that the $1800 electrics were top-quality units that we could rent 20 times a month and know they would perform while the $250 gas washers were the cheapest junk you could find, but as far as getting a job done, being able to repair inexpensively, and bang for the buck, gas is light years ahead of electric. The reason I compare the commercial electrics we had to the cheap gas stuff we sold is because (in terms of performance alone), you can do way more with a $250-350 gas (and repair it for free or $50 when it breaks) compared to doing less work with a $1500 electric that will last a long time. (but cost $400 to repair when if it breaks) It's totally apples and oranges. They are two different machines with two different uses.
TL;DR... if you're looking to squirt some water on your car for washing it 5 times a year, electric is great. If you're looking for doing actual work with it, gas every day and twice on Sunday.
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