I installed a pressure regulation valve in my city water supply because city
pressure is 120 psi. This turned my house piping system into a "closed
system" with no place for the pressure and added volume to go. This results
in water pressure of 150 lbs, which damages my appliances. Turns out that I
now need an expansion tank to absorb the volume and pressure created by the
water being heated. The plumbers I talked to cannot agree on what I should
I have one water HEATER each to supply water to the front and rear of our
home (2 heaters). Both water HEATERS seem to be connected by pipes to ONE
water SOFTENER that supplies both areas (front and back of the house) with
hot, soft water.
How do I install the water heater expansion tank(s)?
Do I install one small expansion tank at one of the heaters, based on the
specs for that heater only (40 gal and 40 lbs pressure), or should I install
a larger expansion tank at the first water heater to allow for the second
and more remote heater, or should I get two small expansion tanks, one at
Both heaters are 40 gal and the house pressure is set for 40 psi.
This suggests the PRV that you purchased/installed does not have a built-in
bypass (which would ensure your "inside" pressure never exceeded that of
the municipal supply).
Yes. You would be surprised how many folks omit this step -- thereby
negating the benefits of the PRV!
If you have a pressure gauge, the easiest way to see this effect is to
take a long shower (i.e., use lots of hot water so the water heater
ends up with a fair amount of cool water that will later expand, on
heating) and then watch the pressure AFTER you've turned off the
water (and don't use any OTHER water until the experiment is over)
Expansion tank(s) need to be upstream from the heaters BUT WITH NO INTERVENING
SHUTOFF VALVES!! I.e., the tank(s) only work if water from the cold water
inlet to the heater(s) can flow BACK to the expansion tank!
Typically, you would install a shutoff on the cold inlet and hot outlet
of the water heater to make servicing easier. When you shut the cold water
inlet valve, a path must continue to exist from the heater to the tank.
Can you do this with a single tank? Or, will you only be able to satisfy
that requirement for ONE of the heaters?
[Imagine having the inlet shut to one of your heaters, the heater full of cold
water AND the heater trying to bring that water up to your hot water
temperature. You now have that same "closed system" -- no place for the
water to "expand BACK into". Just like the problem you described in your
You have to assume, worst case, that both hot water heaters will be full
of cold water (imagine the gas gets shut off at your house for some time;
or, you have house guests who use all the hot water by running multiple
showers concurrently). The expansion tank is sized based on the volume
of water that will be expanding from the heating. So, you have to be
able to accommodate ALL of it.
So, size your tank(s) for 80 gallons total. You can do this as two
tanks (40+40) or one (80). Again, subject to the shutoff valve issue!
If each heater has a shutoff, then treat it as two 40G systems
and provide each with a "local" tank ("local" meaning "within the control
range of that tank's shutoff valve)
I installed pressure gauges on the municipal supply (upstream from the
PRV), the "regulator output" (just downstream of the PRV) and the
load side of the water softener (there is a drop through the softener
and this also lets me monitor for a catastrophic failure of the
softener). These are reassuring -- I can glance over and see that
the pressure is as it should be (and, as our PRV has a bypass, it
is possible for the "inside" pressure to fall BELOW the set point;
but, only if the municipal pressure has also fallen! Hence the desire
to be able to monitor each!)
Run your shower (or otherwise use most of your hot water).
Then, shut off water (don't use any -- hot *or* cold) and
watch pressure slowly climb *upward* from that 60psi as
the COLD water in the heater expands -- into a fixed
geometry space (i.e., pipes remain the same size/volume).
E.g., out "inside" pressure climbs from 50 (the setting
on the PRV) to 100 after a long shower. It *stops* at
100 because our municipal supply happens to be 100 psi
AND our PRV has a builtin bypass (when inside pressure
exceeds supply pressure, PRV "opens" to vent pressure
into the LOWER municipal supply). If our municipal
supply had been 120 psi, then the clamping action
would limit the inside pressure to 120 psi instead of 100.
I'm pretty sure you can install the expansion tank
anyplace in your system as long as it is on the
inside side of the regulator. It is probably better for the
longevity of the tank to install it at a cold water
location. The size of the tank should be large
enough to absorb the expansion of both water heaters.
On 11/20/2015 7:51 PM, firstname.lastname@example.org wrote:
There can't be any shutoffs between the tank and the
inlet of the heater. I.e., the tank needs to be
part of the heater at all times.
Because the bladder in the tank will wear at high temperatures,
it goes on the cold water supply. Note that you need to
isolate it upstream of any heat trap you may have on the
Again, that assumes both heaters can freely exchange water
regardless of the positions of any valves in the system.
Shutoffs tend to be local to the water heater -- to isolate
input and/or output in the event of failure, maintenance,
etc. So, it's quite possible that putting the tank "at"
one heater could result in it being "hydraulically isolated"
from the other water heater. The same can also occur if you
site the tank at the PRV (which is probably remote from the
You also have to consider what may happen in the future.
E.g., when a water heater fails, will a NEW shutoff valve
be installed NEAR the replacement? So, the lack of a shutoff
TODAY might cause you to make a poor tank site selection
choice that impacts what you can ("legally") do in the
[Don't count on that future plumber "doing things right"!
Many of my neighbors have PRV's and AFAICT, I'm the only
person who bothered to install an expansion tank. None
of them were even offered that option at the time their
PRV was installed! (tanks are a PITA compared to something
simple like a PRV)]
Just had my gas storage heater replaced because the tank was leaking.
both the old and the new have a pressure relief valve on the tank and
the correct proceduere is to lift the lever every month or so and
release a little to flush out the salts. In normal use it opens each
time water is used to relaease the pressure.
This quite simple and is the standard way here in AUS.
The "relief valve" (driven by temperature and/or pressure) on
US water heaters typically doesn't operate until ~150psi.
Letting the water system sit at 150psi places undue strain
on appliances, fixtures, etc. (most are designed for 80psi)
Operating the system at a consistent, lower pressure
makes life easier for those appliances -- as well as
helps to conserve water (higher pressure implies higher
flow rates; usually, folks don't finely tune the faucet
for "ideal" flow rate but, rather, get the right temperature
and an approximate rate)
Most folks don't do *any* maintenance on their water
heaters until they fail (at which time, its hardly
called "maintenance"! :> ). Depending on the characteristics
of your water supply and your "maintenance history", opening
*any* valve on the water heater can leave you with a new
problem: a valve that doesn't reseal completely.
[I'm always leary of replacing either the TPR valve or the
drain as they both thread into glass bottles...]
It's NOT a glass bottle. It's a metal with a "glass" lining, which is
more like a ceramic coating. However, if you ever dropped or banged a
ceramic cooking pot or pan or any other ceramic coated cookware, you
have likely seen it chip. So, too much force on a valve or pipe can chip
that coating, exposing bare metal, which is where the tank will rust and
I've often wondered if some anti-sieze (made for bolts) would help to be
put on the threads? (And if it's safe for human consumption, since hot
water is occasionally used for cooking).
The drain valve should be opened at least twice a year (more if the
water contains sediments), and some water drained out. If you dont use
them, they sieze up. The same is true for the TPR valve. I open mine and
release some water the same time I drain water from the drain valve.
Those also can sieze up from lack of use.
Most drain valves these days are plastic. This is good as far as they
dont sieze up as easily, but bad when you have to replace the valve,
because a pipe wrench can break them off, leaving a chunk of plastic in
the threads, which must then be dug out.... easier to dig out than
metal, but metal dont usually break off....
One final thing, drain valves usually have washers, just like many
faucets. They do go bad, just like any washer, and may need to be
replaced at some time. Ideally. they should use a ball valve, but I've
never seen any tank with a ball valve drain. I did replace a drain valve
once, and I used a brass nipple from the tank to the ball valve, and a
NPT to HOSE thread adaptor on the other side of that valve. That worked
great. except I removed the handle from the ball valve, so it would not
get bumped and turned on by accident. I just left the handle next to the
tank for when I needed to drain the tank.
On Sat, 21 Nov 2015 12:50:46 -0600, email@example.com wrote:
Well some are like that, but mine wasn't. It's a Sears Power Miser N,
but I'm pretty sure it's made by A. O. Smith. Everything about it is
the same as the one that came with the house, including the distance
from the input to the output pipes. And I looked at Lowes and HD and
their inter-pipe distances were different. Plus the thermostats are
the same, though I guess that is true for all brands?
Anyhow, the lining is a sheet of vinyl about a quarter inch thick. It
won't break by being banged, in fact I think I would have needed a saw
to damage it. After I sawed the tank into pieces, I eventually,
with a lot of tugging, pulled the liner away from metal, turning it
inside out, and all I would have had to do was turn it inside in and
pushed it back against the metal and it would fit well again.
A little poison won't hurt anyone. Seriously, even right after
installing it it would be diluted 100 to one in the first hour, 1000
to one in the second hour, and even more so after that. And most of
that water would be used in showers and baths.
I hate to say it but when heavy rain makes the stream behind my house
overflow the sewer manhole and that backs up the sewer into my laundry
sink and early on, overflows onto the basement floor, there was no
smell and no sign of solids, while it was wet or after the water
either evaporated or sank through the cement floor (Does it do that?).
Even though it's the sewer. Because the same overflowing stream washed
the solids down the sewer pipe and what backed into my house was
diluted 100,000 to one.
I didn't expect this post to go this way, but....
I have no experience, but a lot of people in this group in the past
have warned against this. They say the valve won't shut afterwards
because sediment will get in and stop it.
They say the same about the TPR.
I do have experience with sediment, however. I cut my old water
heater into pieces in order to throw it away, but mostly to see what
was inside. I was depressed and confused and it probably only needed
a thermostat or two, so I shouldn't have thrown it away so early, but
after 10 years, it had only a tablespoon of sediment in the bottom. At
that rate it would take more than 200 years before the sediment
reached the heating element.
I'm saying it depends on the water supply, and in Baltimore and its
suburbs, maybe it's because all the water comes from 3 large
reservoirs, but it doesn't have much sediment. Washington DC has 2
large reservoirs. Indianapolis has 2. I suspect their water has
I would check with neighbors or the water company to find out the
Ever heard of a backflow valve? They go into the sewer pipe to prevent
water from backing up....
The reason you drain the valve is to REMOVE the sediment. If you begin
draining it the first year it was installed, it should work fine. If it
dont shut off, you need to replace the washer.
It's not a bad idea to drain the whole tank every few years too. Just
shut off the gas valve or electric, before draining it.
On Sat, 21 Nov 2015 12:50:46 -0600, firstname.lastname@example.org wrote:
Generally not a good idea to trip the TPR for "testing" unless you
are prepared to replace it when it doesn't seal properly afterwards -
The higher end units usually have brass sediment drain valves. If you
cheap out and buy one with plastic it is a very good idea to upgrade
them to brass imediately, before they get brittle with age and become
impossible to remove without breaking them.. Put a ball valve on while
you are at it - - -
Use a "lockable" or "tamper proof" ball falve - has a sliding sleave
that must be moved to operate the valve, and can be padlocked or
zip-tied to prevent accidental (or malicious) opperation
Because for many years, municipalities allowed the sort of behavior described by Don Y -- if
the pressure in the residential system rises above the supply pressure, water will be forced
out of the residence and into the supply.
This is now prohibited in many locations, and homes are required to have backflow
preventers to insure that this cannot happen.
Heated water has to expand somewhere, and if it can't expand into the municipal supply,
you'd better have an expansion tank.
You can find lots of videos re: "exploding water heaters". There's a lot
of pent-up pressure in those systems and the heater is often the weakest
Regardless, you don't want to subject the various appliances in your home
(water closets, dishwasher, washing machine, dryer, etc.) to elevated
pressures -- possibly ABOVE their design limits!
Prior to installing the PRV, showers here were delightfully "strong";
as if the water was scraping the dirt from your skin.
OTOH, we had the "fill hose" fail on one WC late one night, "spontaneously".
Similarly, the BRAND NEW (braided steel) supply hose to the washing machine
failed and the resulting water jet cut a hole in the drywall in a matter
Note that as municipalities grow, they RARELY go back and resize the
water mains to accommodate the new "loads". Instead, they just up
the pressure to force more water through the existing pipes. While
the systems *may* have been delivering water at "normal" pressures
originally, chances are these pressures have increased dramatically
over the years.
It's a cheap test: buy a pressure gauge that screws onto a garden
faucet (hose bibb) -- hard to create a pressure-tight seal
on an indoor faucet!
Or, corner the local water department guy when/if you see him in your
neighborhood and ask to borrow theirs (for 30 seconds). Ditto for
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