I have a small handwashing sink in my detached garage that has no hot water. Summertime isn't bad, but winter groundwater temp is pretty cold for handwashing. I don't use it often enough to be worth adding a 110v hot water tank and most of the 110v tankless heaters have horrible reviews or require a 30A circuit. I have a 20A GFI outlet already there and running a 220V supply would not be easy or worth the effort and expense. I was thinking about building a simple RIMS tube with a 120v element that would be controlled by a low voltage flow switch and relay board. I know that it wouldn't supply a high flow of hot water, it'd just be nice to have comfortable water in the winter. My biggest concern would be a switch failure that could lead to the element staying on and creating an overpressure in the tube. I've considered using redundant flow switches and could probably incorporate a water heater pressure relief valve without much trouble. I don't know if there are pressure switches available that could cut power if there was a pressure buildup or not. I know there are people much smarter than me lurking here who's opinions and suggestions I'd love to hear (good or bad). Thanks for any input in advance!