Whisper Wash surface cleaners are one of the best brands of surface cleaners available. I would definitely recommend this product. As long as your machine is rated for at least 4 gpm, you will get a great performance out of this surface cleaner. As far as the gpm rating of this surface cleaner, the total gpm output will depend on the pressure washer that is being used. The flow rate would be dispersed evenly between the 2 nozzles but unfortunately there is no spec provided for the gpm rating of just one nozzle.