"Bob M." wrote:

wrote in message
.. .
I'm in process of replacing my water heater (gas). I've got the new
one out of the carton and it's got all the normal stuff plus something
extra: a bag containing two 3/4" galvanized steel nipples. Each is 2"
long with a blue plastic lining running the length of the inside and
protruding about 1/16" at each end. If I screwed one down on the dip
tube (which seems to be the same color plastic) effectively the water
wouldn't touch the galvanized nipple. I don't know why I'd want this
on the hot side though.

Galvanized pipes rust from the inside out. Good to have both nipples plastic
lined - they last much longer.

Brass lasts even longer. I put back the brass nipples from the old
water heater. It lasted about 14 years and the nipples don't show any
sign of corrosion.

But wait, there's more. At one end of each nipple attached to the blue
plastic lining is a (also) blue plastic ring bringing the outlet
diameter down to 3/8". Inside the ring is a black rubber flap, very
thin, and attached only on one side. Except that it's rubber and
there's a small gap around the black rubber and I can blow the flap
out of the way in either direction, it could be a check valve. There's
no directional arrows on the nipple.

The black rubber thing is a heat trap. Keeps the heat inside the heater
when the thing is not being used. A good idea, but this implementation
needs work if you ask me. See below for a better way.

Why not just put in a proper check valve (brass) on the hot line?
(Personally I don't have the space--the hot and cold lines go straight
into the finished wall--but it's a thought for the future.)

The only reference in the manual is on the repair parts schematic
where these nipples are described as: "Nipple w/Heat Traps". In the
installation section the diagram shows an arrow pointing to the hot
and cold inlets with the description: "3/4" Threaded Nipple". Nothing
about heat traps. The impression is that you could use any 3/4"
nipple.

You can use any 3/4" nipple as long as it's plastic-lined. You just don't
have the heat trapping capabilities with a normal nipple.

Based on my experience the brass nipples don't need to be plastic
lined.

Does anyone have any idea of the function of these special nipples and
which way they go in. I'm a little worried that the rubber flap is so
flimsy that it'll break off and end up blocking some faucet. Maybe
it's a partially disconnected washer (the hole hasn't been properly
punched out) but why would they reduce the size to 3/8"?

No, the rubber flap is the heat trap mechanism. I don't think it matters
which way they go in, if it did the mfgr would likely have arrows painted on
them to indicate the direction of flow.

Yeah, right! This is a manufacturer who obviously didn't think it was
worthwhile to explain what you've just explained. I doubt that I'd
trust them to remember to put arrows on the nipples.

However, I think the things are
likely to be completely ineffective in a few years after the rubber flappers
get permanently bent in the outflow (hot-side) or inflow (cold-side)
directions, or they break off. Plus, they don't truly stop all the heat
from getting out.

A better solution is to make a heat trap out of copper pipe. This kind of
trap is nothing more than a loop. Heat rises, but it doesn't sink, so the
heated water will stay in the tank when hot water is not being used and it
won't radiate heat out the first 10 feet or so of pipe coming out of the
tank.

I have such a trap on my tank and the outlet side of the heat trap is as
cold as the incoming cold water pipe if the tank has been sitting for a
while. My loop was 1/2" copper pipe rising 12" out of the heater's hot
side, then across 2", then back down 12" and out to the house. The length
of the up & down sides of the trap do matter, longer is better up to a
point. 6" probably isn't long enough to truly keep the heat in. (If
necessary, the same kind of trap can be applied on the cold water side, but
it probably isn't necessary; the dip tube does the trick there.)

Because this involves laws of physics, it will always work and it will never
have a piece break off and plug up something. Supposedly you can take a long
length of that so-called "flexible" copper pipe and make a loop out of it -
it would do the same thing - but have you ever tried to bend that stuff?

I thought the flexible copper type had been banned? Anyway, my big box
stores only sell the braided stainless steel type and I can't see
bending one of those into a loop.

Thanks for the info.