Do I need 12” vertical brass stubs on this Rheem Water Heater?

Question

I’m installing a Rheem Marathon electric 50-gal water heater, in a 2nd floor, where it’ll service only the 1st floor (so it kinda has a “built in” heat trap since the pipe only goes down). Been trying to contact Rheem for 2 weeks with no response. There’s no code official here for me to ask either (unincorporated area). I want to follow best practices to ensure safety and performance.

1. The manual says "pre-solder 12" minimum stub pipes before installing to unit." We don’t use copper here due to water composition. I could use a brass nipple, but I want to be sure I understand the purpose of this requirement. Is it: -(a) to ensure vertical clearance (which I’ll have regardless) -(b) to ensure that a plumber does not melt plastic components while soldering < 12" from the inlet/outlet (irrelevant to me) -(c) to make sure there is not a pressure "bottleneck" at the tank whether for safety or water pressure issues (good reason!) -(d) some other reason?

2. If I do need to put 12” of brass here... does it have to be vertical? Or could I instead attach a brass street elbow directly to the inlet/outlet, then put the brass nipple horizontal? Again I don’t want to mess with water pressure or safety. --And if it does have to be vertical, then why Terry ok here? https://youtu.be/m598ynGCg74. (I trust him over the manual that came with my heater, which is generic for all Rheem tank models). Thing is, my installation will be all hard piped.

3. The unit is being plumbed with Pex-A (Uponor) which is rated for direct connection to a water heater. Manual p. 8 says "Hot water connection fitting must have an ID > 0.725”." I can accomplish that with a 3/4" brass nipple, which I will then adapt to Pex-A (0.681" ID) - but is there a minimum length required for that nipple?

Not trying to cut corners at all – just want to understand the purpose behind the instructions so I can do what’s best in this situation. Thanks!

Answer 1

1. Is about soldering to the pipe stub, and does not apply. Even if you don't have a local code official in your unincorporated area, you may have state codes that apply, technically. In my state we are supposed to have 3 feet of metal pipe before any plastic pipe, no matter how rated (annoying local code modification.) Stainless steel pipe is more resistant to most types of corrosion and usually cheaper than brass pipe.
2. Does not, therefore, apply.
3. Does not seem concerning, since it's going into that size anyway. If your plumbing setup allows, you could perhaps find a 3/4" NPTM-1"PEX fitting, and run the 1" PEX to the first Tee in the hot water line, to be fussy about it.

You DO need a vacuum breaker on the cold line, since the water heater is above all (or any of) the outlets. The tank can be crushed by vacuum if the supply is off and the outlets below the tank are open. That should be between the tank and any valve on the supply.