Water heater expansion tank conundrum

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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 do:
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 each heater?
Both heaters are 40 gal and the house pressure is set for 40 psi.
Thanks
Walter
www.rationality.net
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On 11/20/2015 5:48 PM, Walter E. wrote:

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 opening statement!]

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!)
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Walter E. wrote:

Pressure regulator valve is not enough? Our house has regulator and when water is running it is 60psi. We don't need anything extra.
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On 11/20/2015 6:52 PM, Tony Hwang wrote:

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.
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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.
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On 11/20/2015 7:51 PM, snipped-for-privacy@yahoo.com 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 water heater.

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 water heater.
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 future.
[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)]
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on 21/11/2015, Don Y supposed :

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.
--
John G Sydney.

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On 11/20/2015 9:03 PM, John G wrote:

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...]
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Don Y wrote:

Best hot water tank I had is Sears Power Miser 9. Going on 16th year w/o a single problem. Knock the wood now.
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On 11/20/2015 11:09 PM, Tony Hwang wrote:

The Rheem we had when we moved into this house lasted 20 years while *we* were here -- no idea how long BEFORE we bought the place it began serving that purpose!
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On Fri, 20 Nov 2015 21:29:05 -0700, Don Y

I keep hearing about glass lined WHeaters, but mine was metal with a vinyl lining. There may have been glass embedded in the vinyl, but there were no sharp edges.
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wrote:

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 eventually leak.
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.
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On Sat, 21 Nov 2015 12:50:46 -0600, snipped-for-privacy@unlisted.moc 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 little sediment.
I would check with neighbors or the water company to find out the local situation.

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wrote:

I forgot to say that these are electric WHs. I presume they make gas ones the same way.
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wrote:

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.
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On Sat, 21 Nov 2015 13:59:19 -0600, snipped-for-privacy@unlisted.moc wrote:

Yes. It didn't work well enough. This was discussed at length here.

I know. I'm just telling what other people have said. And that I had only a tablespoon of sediment after 10 years, without ever having drained anything.

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On Sat, 21 Nov 2015 12:50:46 -0600, snipped-for-privacy@unlisted.moc 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 - from expeience.

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 - - -

that must be moved to operate the valve, and can be padlocked or zip-tied to prevent accidental (or malicious) opperation

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On Fri, 20 Nov 2015 20:42:36 -0700, Don Y

How ddid we get along without these tanks for so many years?
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4ax.com:

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.
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On 11/21/2015 10:55 AM, Doug Miller wrote:

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 link.
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 of seconds!
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 any plumber.
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