Hi. I've been lurking out on your site for several weeks now and have had many questions answered from viewing old post. I am currently adding an addition to my house and I am interested in installing a 2.5 gal inline hot water heater so I don't have to wait forever for hot water. My question is how can a properly hook up a emergency use only drain for the pressure relief valve? I am fortunate that the location of the new hw heater is in the same 2x8 wall where the drain stack is located and I still have access to all the drain pipes the plumber installed for a sink. There is a 1 1/2" waste line that runs directly below the location of the new HW heater and a vent line that runs 46" above the new HW heater. I am afraid that if I just add a T and run a flex line from the relief value to a open pipe it will let out a smell where the two join or water could come out if I ever have a back-up. Should I be worried this much about the relief valve ever needing to operate and cause me issues? Should I call my plumber back for a beer and get his professional opinion?

Any code I should be worried about with installing a Bosch 2.5 gal electric heater? I planning on just extending the 2x8 wall where I'll create a shelf with a door to set the unit on.