I've been doing a lot of reading, and I kept seeing some people recommending 18" of metal supply line clearance from water heaters, some saying it doens't matter, and some saying contact the manufacturer. I just did the latter, and thought I'd post their comments and solicit the forum.
I called Paloma (aka Rheem) and talked to their technical support person. He said there is no need for 18" of metal pipe clearance from the tankless water heaters - I could run pex all the way up to and out of it (minus the drains, check valves, pressure relief etc - they would be copper).
I'm curious why the 18" recommendation from folks - these units themselves have negligable clearances, and the temperature is set at a specific temp (ie. 120 degrees, and most pex is rated at 180 deg or higher). I can understand clearance from the vent itself, but my water supplies are on the bottom, and the vent on the top. Or is this a plumbing code that must be followed?
Forgive my curiousity, I'm an engineer and I just have to understand the WHY?
12-18" is a carry over from gas water tanks where the outlets were close to the draft hood which always spills till drafting starts and is hot from the radiant heat
No need for leaders on a tankless.