Connecting water pipes to a domestic hot water heater. Plumbing With Copper Pipe:

Connecting Pipes To A
Domestic Hot Water Heater

In This Article:

The galvanized pipe stubs are extended and dielectric unions attached. Copper pipe is soldered to the hot and cold connections.

Related Articles:
Skill Level: 3 (Moderate) Time Taken: 2 Hours

By , Editor


Connecting a new water heater is not a difficult job, but it does require some plumbing skills. This article follows some of the procedures used to connect a water heater to existing copper pipes.

The location of the water heater can depend on several factors. This heater is gas-fired so it needs a chimney for exhaust fumes, but it has a "forced draft" fan, so the vent can be directed out the basement wall. Electric water heaters need no exhaust venting, so they can usually be placed anywhere that makes sense.

The water heater is connected to the plumbing system by a pair of threaded pipe stubs. I applied a generous coating of pipe thread compound.
Then I installed a galvanized coupling.


I installed a 6" galvanized nipple (short piece of pipe). There was not enough space to put the union fitting directly on the stub, so I used the 6" nipple as an extender.
On the cold side, I did the same, but used a 3" nipple.


Dielectric union fitting. This device is a dielectric union. It electrically separates the water heater from the household piping.

Read more about dielectric unions, and why they are necessary.


A short piece of pipe was soldered to the brass part of the union.
Next I soldered a threaded male adapter fitting onto the other end of the pipe. This end will connect to a shutoff valve.

Why not use the cheaper valves, which are soldered directly to the pipe? Personally, I'm not that good at soldering pipe joints, and in the past I have melted the plastic components on a few valves, especially ball valves.  I probably apply more heat to the joint than most professional plumbers do, but I don't solder pipes every day, so I get out of practice.

(I've learned over the years that wrapping a wet rag over the valve body helps to prevent the plastic parts from melting. Also, using a MAPP gas torch, which burns hotter than propane, gets the soldering done faster so there's less time for the plastic parts to heat up.)


Dielectric union fitting between copper and galvanized pipe. One union was connected to the hot water side.


On the cold water side, I installed a 3/4" diameter ball valve, which only requires a quarter of a turn to shut off the water.


The Existing Supply Lines:

This house had been plumbed several months before, and the plumber had tied the hot water line in with the cold.  I used a pipe cutter to remove this section.
Even though the water had been shut off for over an hour, I still had quite a trickle.


With both hot and cold sides trimmed back, I let the system continue to drain while I prepared the other sections of pipe.
I cut the lengths of pipe needed to connect the cold water supply to the inlet side of the water heater. Where possible I solder the fittings on a workbench.


I soldered the fittings in place. I put a metal heat shield behind the pipe to protect the floor joists from the flame.
The cold water line was very close to the PVC vent pipe, so I squeezed the heat shield in there, too.

Be careful with heat shields.  Make sure the heat shield does not cause the torch's heat to build up, as in this rather shocking story.


Hot and cold water pipes connected to a water heater. Looking up from almost floor level...

This is a view of the pipes that connected the water heater. Note the furnace duct directly above the water heater. This kind of obstruction is quite common.


A typical soldered fitting. 

There is a small ring of solder visible around the joint. By wiping the joint with a wet rag a minute after soldering, a clean-looking connection can be made. This also removes most of the solder flux, which can corrode the copper surface after a few months. 


But... I used to wipe the joints immediately after soldering, because I had worked with experienced plumbers that did that all the time.  Except that I wasn't quite so experienced, so I ended up heating the joint a little more than necessary (not a problem in itself) and when I wiped the excess solder off, the solder hadn't hardened yet, so the fitting would move, and then harden, and this motion would disrupt the pool of liquid metal as it solidified, or something.

Anyways, too many of these connections would leak. So I stopped wiping the joints right away. I now spray some water on the joint, then I wipe it.


We used perforated steel strapping to support the pipes. This was held in place with 1/2" sheet metal screws.

There are many different types of pipe hangers available. This method is probably the cheapest but takes more time than others. Plastic pipe hangers are better because they won't corrode and they don't make noise when the pipes expand.



Tools Used:

  • Pipe Cutter
  • Pipe Cleaning Brush
  • Propane Torch
  • Pipe Wrenches
  • 15" Adjustable Wrench
  • Tape Measure

Materials Used:

  • Dielectric Union Fittings
  • Galvanized Nipples, Couplings
  • Copper Pipe, 3/4"
  • Copper Pipe Elbows, Threaded Adapters
  • Silver Solder


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Copyright © 2000, 2005

Written January 29, 2000
Revised January 12, 2005