I'm having a new water heater installed soon. I'm told my state (NJ)
requires a bonding cable be installed between the hot and cold water
I'm wondering if there is any benefit to also requesting a dielectric
fitting be installed intstead of standard copper fittings. If a
bonding cable is used, does this make the the dielectric fitting
unnecessary if my goal is to prevent corrision at the connections?
Is there any benefit to also requesting the use of a dielectric
If your place is plumbed with copper then you'll do best to stick with
all copper/brass right up to the heater tank's cold and hot ports.
Rheem stopped recommending dielectric unions on their water heaters a
few years ago:
I'm sure I've mentioned this before, but about four years ago when I
last replaced our electric water heater, I slavishly installed a pair of
dielectric unions at the inlet and outlet ports, replacing the all
copper ones which were there before. I used a pair of short iron nipples
between the tank ports and the iron sides of the unions. Those nipples
clogged with soft rust and one of them sprang a leak in just a few months.
Here's the leaking nipple, after I sliced it down the midline and
scraped out most of the rust:
I thought things through and realized the dielectric unions were
effectively "shorted out" because the heater tank was grounded per code
as was the copper piping in our home, so they weren't helping at all.
I replaced those dielectric unions and the iron nipples with all
copper/brass fittings and things have been fine since.
The insides of the iron nipples took the brunt of the galvanic corrosion
because they were electric field wise "out of sight" of the sacrificial
anode rod in the tank.
I'm planning on installing an AO smith and in their instructions they
strongly recommend dielectric unions. My pipes are copper. I had
thought the connection on the heater itself is stainless steel, is
that incorrect? Wondering if the treads are wrapped with teflon tape
that the teflon has any dielectric effect? Do you think I should
igore what the Smith manual says:
"NOTE: To protect against untimely corrosion of hot and cold
water fittings, it is strongly recommended that di-electric unions
or couplings be installed on this water heater when connected
to copper pipe."
I would follow the manufactuers recomendations, dis similiar metals do
have you looked at the very high efficency gas water heaters tank type
the 96% efficency ones?
upfront costs are higher but first hour ratings capacity etc are
The bonding jumper is required so that the hot and cold water pipes are at
the same ground potential. It does not have to be at the water heater, it's
just that it's the easiest place for the inspector to find it. Use at least
a #6 copper wire, but I prefer #4.
Dielectric fittings are used to help reduce corrosion of your water heater.
A plumbing permit is required to replace a water heater, but this can be
applied for after the installation due to an emergency. I've had a few
customers tell me that when the gas water heater was replaced, the exhaust
vent had to be enlarged due to the higher BTU rating of the new gas water
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