I want to install a point of use water heater for the future sink in my shop. Basically, this sink will just be used for cleaning brushes, watering plants, washing hands, etc. This will not be inline with another water heater; it will be the sole source of hot water. I don't know anything about these heaters but I see they come in different sizes, 2, 4, 6 gallon. Could I get some advice on these things? What size do you think I'd need for what I'd be using it for?