Is it possible to pre-assemble and pre-solder copper pipes into a subassembly that then can be installed using a threaded fitting? I'd much rather solder the joints either in an oven environment or on a workbench than sweat them right up against my water heater. This is for a downpipe drain on a water heater T&P valve -- our heater currently lacks the downpipe, with the T&P just "spitting" sideways. The valve in question has internal threads on its downstream (open to air) end, by the way.

Also -- copper is the material I want to use here -- last I heard, PEX isn't code-compliant where I live, and I would not want to use it anyway due to the prospect of material damage if the T&P ever had to function in anger.

  • I can't speak to how backwards your codes may or may not be, but either PEX or CPVC work fine for a discharge tube - hot water does not bother them.
    – Ecnerwal
    Dec 5, 2014 at 3:09
  • @Ecnerwal -- my concerns relate to the potential for scalding hot water or flashed steam coming down the drainpipe, which are outside the working range of PEX. Dec 5, 2014 at 3:20
  • And yet it will work fine, because it's an open bottom drain tube for a very finite amount of discharge, not a pipe under pressure nor subject to continuous flow.
    – Ecnerwal
    Dec 5, 2014 at 3:30

1 Answer 1


Yes, it's possible to bench solder, and in fact you should generally avoid soldering on an assembled threaded assembly. "Oven soldering" is a completely absurd approach to plumbing. Save it for your SMT electronics projects.

If you are very uncomfortable about soldering, just use threaded pipe (steel, brass, stainless steel...) and threaded fittings.

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