If you have a Rheem tankless water heater or are thinking of getting one, you should be aware they have a little noticed requirement in their installation instructions it might be wise to think about or consider.
Note the 3rd bullet point. While the 2nd specifies the unit must be properly grounded, it states the unit is NOT to be installed on circuits that require AFCI or GFCI protection.
I found this troubling and baffling so I called Rheem technical support. I was informed that the unit WILL trip AFCI and GFCI devices. It is called nusiance tripping, and periodically having to reset the breaker is not desirable.
I specifically asked what a customer should do that wants to install a unit where AFCI and/or GFCI protection was required, and was told, "find another location to install it."
Now this is problematic, as in most jurisdictions that have adopted recent electrical codes, there are very few such locations any longer. Almost all locations where one would want to locate one of these units now falls under either AFCI or GFCI protection---and sometimes both.
So outdoors is out.
The garage is out.
The basement is out.
This leaves the attic.
Of course the attic is problematic for other reasons. Leaks, attic temperatures that might necessitate installation of tempering valves as the water lines heat above 120 degrees F.
I have not yet found another tankless manufacturer that has this issue and I would be surprised if Rheem is not working on a solution to this problem.
With coming code changes, I suspect the receptacles in even the attic will require either/and/or AFCI / GFCI protection. This is just the way the codes have been moving---are moving.
Charles Buell, Real Estate Inspections in Seattle