I'm replacing the pipe and valves serving outside water faucets
in a recently purchased house near Fairbanks, Alaska. It's all
3/4" L copper pipe. My question: Am I required to put a union
anywhere in this pipe?
I ask because I've read that unions are required in some of the
piping for hot water heaters, so I figure they may be required
elsewhere, too. Also, the pipe I'm replacing has unions in it,
but I'd rather not put them in the replacement pipe, if I can
legally do so. BTW, I've looked at codecheck.com, but I cannot
find anything relevant.
And if anyone knows any other issues I should be aware of, go
ahead and mention them ....
Last (and certainly least) can anyone tell me *why* unions are
sometimes required? They strike me as an unreliable nuisance.
I certainly do not know anything about your local codes, but as for unions:
they are intended to make future maintenance easier. In theory, a pipe that is
connected to another with a union can be taken apart and put back together with
a pipe wrench. I have installed water heaters both ways. The only time the
unions came in handy was when were rebuilding our 1884 Victorian and had to
relocate the plumbing (several times).
As for outside faucets in a cold climate, union joints could make it easier to
replace something in the event that a sudden freeze came a long and the outside
water had not been shut off and drained.
Just thoughts from someone who hates plumbing. :-)
New Eagle, PA
The best reason for a union at a water heater is that it makes it easier
for the water heater to be removed or replaced. I used about 1 foot long
flexible pipes, sold as a water heater hookup kit, for myself, it made
installation a snap.
A friend soldered together the pipes to/from his water heater, a real
task, and one he will have to repeat if he gets a new heater, which has
different pipe spacing.
Another reason for a union is to join dissimilar pipe, like copper and
iron, then you need a di-electric union which isolates the pipes
electrically from each other, to prevent galvanic corrosion. You need to
jump around the union with wire, to insure electrical continuity.
Use the frost free outdoor faucets, that have the valve part way back,
where it is enclosed in the insulation, which you have to repack in
after installing the faucet.
They would be required any time there is a possible need to take the
pipe apart in the future. Unions are no less reliable than any other
threaded pipe connection, of which there are millions in the world, that
And if you do that jumping around thing you will completely negate the
benefit of putting a dielectric union in there and have just wasted
money and time on it. Dielectric unions only prevent corrosion where the
dissimilar metal pipes join if there is NO other low resistance
electrical path connecting the pipes to complete the circuit for the
There are some "galvanic isolators" which provide the electrical
equivalent of six inches or more of "plastic pipe" jointing the two
dissimilar pipes. These aren't perfect, but they do help even if the two
pipes are electrically connected together because they create a longer
water path between the two dissimilar metals, and since typical
household water is far from being a low resistance conductor, the
galvanic current flow is reduced by the longer water path's resistance
and "deplates" the less noble metal slower.
At least that's the way I learned it from Grandma...
Thanks to all who replied, and especially for the pointers to frost
free sillcocks, which I had not heard of before.
I still don't like unions, though. Do a quick search for "leaking
union", and you'll see that I'm not alone ....
Seems you don't like unions. Loosening a union nut sure beats having
to cut tubing/pipe or piece-by-piece disassembly to replace stuff like
Last year I had to cut out my leaking water-heater. There's a
sweat-union in both lines now, you can be sure, with a shut-off
physically above each.
There are all sorts of unions, which indicates to me that there are
many uses for them. The only reason I can think of why you might avoid
using union(s) is that they cost more than same length of tube/pipe.
They strike me as extremely reliable, desirable fittings to civilize
pipework. Line up the halves, sock down the nut, done. Couldn't be
much simpler- just gotta have the piping done so the union halves are
Not required as far as I know. A Union may not make the job easier either.
It will need to be soldered on each end anyway. The, soldered on, union half
most likely would not facilitate replacing the outside valve any easier -
which is their purpose. I would, and do, leave them out of the equation for
outside faucets. I do use shut-off valves with a drain in addition to a
frost free sill cock. Lets me drain the water away from the valve just in
No, you don't have to use union anywhere on copper water pipe.
A day after I put my water heater in 2 years ago I read the instructions.
(Better late than never) Not using unions voids the warranty because the
heat of a sweat fitting can damage the plastic lining on the pipes going
into the heater. Doesn't seem to have done mine any harm though.
It is probably also easier, as the other guys said.
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