awells218 I've seen a few commercial TWH that are NSF approved from Noritz, but I don't know much about them since my company only really deals in electric booster heaters. I will say that in most cases with customers I've seen where the question of NSF or non-NSF is the issue its almost always better safe than sorry. Even if your HD says its ok for now you never know when regulations will change, then you could wind up spending even more money for a second water heater that meets the standards. Just a thought.
In all the build/threads on this forum, I have never
read anyone saying their HD even asked if a IWH was NSF approved. Never. And in most health departments if they change a rule your usually given more than ample time (year or more) to make the change. The cost difference is outrageous.
The HD checks water temps and the cheap brand that is often referenced here on RF puts out water hot enough that it steams. What more could you ask for? I would bet some serious money if the issue is not raised by the builder it will never come up. Beside that they take about 20 minutes to change. I have replaced two because they froze up in sever winter storms when I ran out of propane in the trailer. Both instances were due to my neglect not keeping a sharp eye on the propane level. No propane and the trailer heaters go off and everything freezes.