I'm buying a new water heater, and quite frankly the series of connections and valves are mind boggling. What I'd like to do rather than soldier the pipes together is to go from compression to thread. I have 3/4 ID (inner diameter), 7/8 OD (outer diameter) feeding the water heater. From that point there are a series of elbows and a valve I don't trust taking the copper pipe to the water heater.

I'd like to cut them off, and put on a compression fitting and flex tube to the water heater. Is there anything wrong with this idea? Moreover, what kind of valves and adapters do I use?

Ideally, there would be a combo-valve that would go from 3/4 compression to thread, and then from a mail thread I could use a flex pipe to go right to the heater.. This valve doesn't exist, but such a setup would result in one compression rings per water line.

What does exist is compression-compression-valves, but in this configuration I'm adding two more compression rings per side of the water heater which is far from ideal. I assume this is a bad idea? I've ruled this out.

So, it seems I could go from 3/4 to NPT right away. Then I could use Female NPT-NPT valve. But, I can't find the 3/4-3/4 male NPT coupling fitting to tie the female flex pipe into the female valve.

3/4 pipe → 3/4 compression female to NPT male → NPT female to NPT female valve → NPT female valve to NPT male-male coupling → NPT male-male coupling to NPT female flex pipe.

And none of these parts are carried by anyone retail store... So what's the right and easy way to do this? I've had very good luck with compression fittings.

2 Answers 2


Assuming that your HWT connections are 3/4 MIP and starting from the tank working back the the pipe at the wall:

Cold Side

  1. 3/4 FIP x 3/4 MIP Flex Hose

3/4 FIP x 3/4 MIP Flex Hose

  1. 3/4 Threaded Ball Valve

enter image description here

  1. 7/8 x 3/4 Brass Compression x MPT Adapter

enter image description here

Hot Side

  1. 3/4 FIP x 3/4 FIP Flex Hose

enter image description here

  1. 7/8 x 3/4 Brass Compression x MPT Adapter

enter image description here

(No need for valve as the valve on the cold will isolate the hot)

No need to use these particular brands, they are just the first ones I found. All items should be available on Amazon or a local hardware store.

  • Is there any reason to not put a valve on the hot too? I mean, this is a tight fight. If I ever want to take it out for maintenance I may not want to have the pipes drip all over the place again. (and, we're only talking another $10) Nit to mention it's not really isolated. I have a sink that has a hot-cold single swing thing that seems to feed back cold water the other way. (that would be my guess anyway). Dec 22, 2015 at 0:48
  • 1
    Valves are typically not put on the hot side as they are redundant. It won't hurt the system to have one but it's an unnecessary added cost. If you feel the added cost is worth it for you then that's fine.
    – pdd
    Dec 22, 2015 at 20:29

In addition to PDD's suggestions, you will also want to retrofit your tank with a curved dip tube (available through waterheaterrescue.com -- I'm not affiliated at all with them) and another ball valve to replace the existing, easily-clogged tank drain. Strapping the tank with sturdy metal straps to structural members is also highly recommended (and required by code in seismic zones).

These, along with regular flushing of the tank and periodic anode replacements (unless you're the OP experimenting with a stainless steel tank, which doesn't have an anode to replace), will mean your heater stands a good chance of far outliving its warranty, instead of becoming a consumable due for replacement in six to fifteen years.

  • I'm getting a new stainless steel tank that doesn't need an anode. homedepot.com/p/… Dec 22, 2015 at 0:15
  • 1
    Also, you probably want to purchase a water heater tank strap. These are code required (at least in SoCal) to keep the tank from toppling over from any forsaken god act's.
    – ojait
    Dec 22, 2015 at 1:20

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