Thermal expansion and water hammer arrestor - three questions

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meeotch

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I just had my 40 gal water heater replaced. On its first heating cycle, the pressure release line squirted out 1-2 cups of water. I opened the manual, and on page 6 was a giant warning about thermal expansion tanks being required in the presence of a backflow preventer (which my building does have). I called a couple plumbers, including the one who installed the new heater, and was told, "Thermal expansion tanks generally aren't installed, especially for a small tank like that."

Bought a pressure gauge, and got the following results:
  • House pressure was ~45 psi "at rest" - seems good to me
  • Tank pressure after taking a 5-10 min shower rose to ~65 psi about 10 min afterward - obviously thermal expansion, but it seems within acceptable limits. (Google says 80+ psi is dangerous.)
  • Ran the hot until it went lukewarm. Tank pressure rose to 150 psi over the course of an hour, then the relief valve squirted out a small amount of water.
So it seems clear to me that I need a TE tank, unless I want to limit the length of my showers, or leave the tap dripping for a while after I take a long shower.

The tank is under a staircase in a storage area, space is limited, and the tank connections are already a bit of a copper knot, due to the hot/cold supply lines being installed backwards (hot on the right, cold on the left) by a previous plumber. So installation of a TE tank at the water heater is not ideal.

Question #1: Am I correct that the TE tank can be anywhere in the system, and that it can be connected with flexible hose (this is NYC)? Specifically, I'd like to put it under the kitchen sink, and connect it to the braided flex hose that feeds the cold water to the faucet. It seems like this would be simple enough that I could do it myself, no soldering.

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Separate issue: I get water hammer whenever I turn off the taps (not while running). The sound doesn't bother me, but I'm concerned about stress it may by putting on the system.

The domestic system goes roughly like this: street -> backflow preventer -> water heater -> bathroom sink -> toilet -> kitchen sink. (No dishwasher.)

Question #2: Is it correct that water hammer arrestors need to be placed between the supply and the fixtures? The only exposed pipe that's upstream of both sinks & toilet is at the water heater. The other available location is at the "end of the line" under the kitchen sink. (Is it possible to install an arrestor on flexible hose, under the sink - and will that protect against hammer from the other fixtures?)

Question #3: Will the thermal expansion tank serve the same purpose as a hammer arrestor for the cold line, if placed at the water heater supply, rather than under the kitchen sink? Or are they different animals, and I really need both?

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Of course, I can consult a local plumber for expert advice on these issues. But as you might gather from the above, I've already fallen into a situation where the local experts don't seem to be following best practices.

UPDATE: I should mention that there's probably only 30-40' of total pipe between all of the fixtures. 10' from the heater to the bath sink, then 10' to the toilet, then 10' to the kitchen sink. Unfortunately, all of it is behind drywall except a short tangled section of copper between the heater and its feeds, and then the flexible part under the kitchen sink. (Bath sink flex hose is exposed, and it would be ugly to install anything there.)

I've added a photo of the under-sink area. The plan would be to install a tee on the cold flexible hose, and stash the TE tank in the corner.

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Reach4

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So it seems clear to me that I need a TE tank, unless I want to limit the length of my showers, or leave the tap dripping for a while after I take a long shower.
Agree.
Question #1: Am I correct that the TE tank can be anywhere in the system, and that it can be connected with flexible hose (this is NYC)? Specifically, I'd like to put it under the kitchen sink, and connect it to the braided flex hose that feeds the cold water to the faucet. It seems like this would be simple enough that I could do it myself, no soldering.
I think that could work. There may be some who dislike that.

There are ways to tee off the connection. Those tanks have a 3/4 NPT thread, so you will need to use some adapter(s).

Question #2: Is it correct that water hammer arrestors need to be placed between the supply and the fixtures? The only exposed pipe that's upstream of both sinks & toilet is at the water heater.
The closer to the valve, the better. For faucets, you can just learn to close the faucet more slowly, but for dishwashers, those have fast valves.
Question #3: Will the thermal expansion tank serve the same purpose as a hammer arrestor for the cold line, if placed at the water heater supply, rather than under the kitchen sink? Or are they different animals, and I really need both?
If the tank is under the sink teed off of the cold, that would do double duty. Dishwasher is normally only connected to hot.
 

Jeff H Young

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1 E T should be installed between shut off to water heater and tank but other wise anywhere . and yes you need it.
2 closer to the fixture is best
3 E T does not take place of an Arestor
 

meeotch

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Thanks for the quick replies. Sounds like opinions vary a bit, but still, good info.

I've updated the original post with a photo of the under-sink area, and in particular the flexible hose feeding the faucet, plus some info about the size of the system.

Do they make water hammer arrestors that are compatible with flexible hose? The simplest of all possible worlds would be for me to put the TE tank under the sink on the cold water hose, and then an arrestor on the hot water hose. Wait and see if there's still hammer on the cold line when I turn the faucet off. If so, add another arrestor on the cold sink flex.

But that would be downstream from the bath sink & toilet, so I don't know if that will protect from water hammer from those fixtures. If not, then the only other option is at the water heater, which is upstream from everything else.
 
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Jeff H Young

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expansion tank will work like that just fine but doesn't meet the requirement of code, because it is on wrong side of valve to water heater .
usually we change the angle stop to one with a built on hammer arrestor. never saw one as you describe but perhaps available? but put the hammer arrestors right under sink yes
 

Reach4

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expansion tank will work like that just fine but dosent meet the requirement of code, because it is on wrong side of valve to water heater .
Does UPC 602.3 actually specify the thermal expansion tank not have a valve between it and the WH? http://forms.iapmo.org/email_marketing/codespotlight/2018/aug16.htm

IPC says
2018 IPC 607.3 Thermal expansion control Where a storage water heater is supplied with cold water that passes through a check valve, pressure reducing valve or backflow preventer, a thermal expansion control device shall be connected to the water heater cold water supply pipe at a point that is downstream of all check valves, pressure reducing valves and backflow preventers.​
No statement about needing to be downstream of the shutoff valve.

I don't have a thermal expansion tank because I have a well pressure tank.
 
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meeotch

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Terrific - thanks for the replies. Sounds like I might be able to do this incrementally. For less than $100, I can put the TE tank & arrestors on the flex under the sink. Run my pressure tests again, see if it fixes the problems. If not, hire someone to figure out how to wedge the TE tank in the "proper" place, between the heater and the heater shutoff valve.

In defense of what probably sounds like I'm being a cheapskate: You'd really have to know the special hell of trying to get anything done with contractors in NYC. I've dumped thousands of $ into the plumbing in my place - multiple backflow devices, sinks, water heater, etc. All with licensed pros with good online reviews. And every time I hire a new one, they tell me the last one did something the wrong way. It's both gratifying and terrifying that I needed to discover this thermal expansion thing in the heater manual myself, rather than having an expert warn me ahead of time. No offense intended to the trades... it's just really a crapshoot in NYC, for some reason. Maybe something in the water? o_O
 

Reach4

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In defense of what probably sounds like I'm being a cheapskate: You'd really have to know the special hell of trying to get anything done with contractors in NYC. I've dumped thousands of $ into the plumbing in my place - multiple backflow devices, sinks, water heater, etc. All with licensed pros with good online reviews. And every time I hire a new one, they tell me the last one did something the wrong way. It's both gratifying and terrifying that I needed to discover this thermal expansion thing in the heater manual myself, rather than having an expert warn me ahead of time. No offense intended to the trades... it's just really a crapshoot in NYC, for some reason. Maybe something in the water? o_O
You might want to change your location to NYC from New York. Or maybe Manhattan if appropriate. Plumbing in NYC has its own rules, but then it is dealing with a very high density.

Sylvan has an NYC plumbing company. I think they do mostly commercial.
 

Jeff H Young

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Does UPC 602.3 actually specify the thermal expansion tank not have a valve between it and the WH?

Thanks Reach 4 I guess ipc allows expansion tank anywhere in system and might not even mater the pipe sizing as a kitchen sink is usualy a half inch line. Ill now check my UPC code and see if that kind of work is allowed in my code. but in any case it should work but I think thats a funny way to plumb it.

I don't have a thermal expansion tank because I have a well pressure tank.
 

jadnashua

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You could consider a shutoff valve a backflow valve as when it's closed, nothing can back flow through it...the idea is, you want the ET to always be able to accept the expansion, regardless of whatever dumb thing you might do like shutting the supply while leaving the tank running.

But, it will work anywhere between the WH and anything that would otherwise prevent water from getting to it during normal operations. While many ETs are not specified for use on the hot side, but technically, it would work on that side, too, IF you bought one certified for use with hot water. One designed for BOTH hydronic AND potable water would work anywhere, but likely last longer on the cold side.
 

Jeff H Young

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You could consider a shutoff valve a backflow valve as when it's closed, nothing can back flow through it...the idea is, you want the ET to always be able to accept the expansion, regardless of whatever dumb thing you might do like shutting the supply while leaving the tank running.

But, it will work anywhere between the WH and anything that would otherwise prevent water from getting to it during normal operations. While many ETs are not specified for use on the hot side, but technically, it would work on that side, too, IF you bought one certified for use with hot water. One designed for BOTH hydronic AND potable water would work anywhere, but likely last longer on the cold side.
Did a little reading myself don't see anything specific to a shutoff valve being allowed downstream of expansion tank. I can tell you I looked at manufacture instructions and they have a poor drawing but shows no valves between the 2 tanks.
All the new homes I've plumbed or commercial jobs plumbed by me or other professionals I've never seen an expansion tank installed upstream of a water heater shut off valve. Its been rammed into my head for a few decades how we do it , but also entirely possible that I'm wrong, and I can't totally support my opinion at this time.
 

Sylvan

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You might want to change your location to NYC from New York. Or maybe Manhattan if appropriate. Plumbing in NYC has its own rules, but then it is dealing with a very high density.

Sylvan has an NYC plumbing company. I think they do mostly commercial.


Actually my company does commercial, industrial, residential and institutional and boiler installations and inspections


I work as an expert witness going against unscrupulous land lords and inept plumbing contractors


My other company strictly fire suppression and the last major job we did was on the 86 floor of the Empire state building

From one family homes to high rise residential along with water Jetting line up to 30" and as small was 3/4"

Sewer and drain cleaning actually pays a lot more then "plumbing"


Now with the new gas laws in effect my partner completed the 32 hour classes and has a back flow testing certification


Not too shabby for a guy who came to America less then 6 years ago waiting for his citizenship papers

He also completed along with the other employees all the required OSHA courses

sylvan-boiler-02.jpg
 

meeotch

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Thanks for the continued input. I didn't expect this thread to have such long legs. (It's a good thing!)

The heater manual actually says: "install an expansion tank in the cold water line between the water heater and the check valve". This was the part that I was most concerned about - whether there was something special about that specific placement, upstream of the heater. But it sounds like maybe it's just because, as Jim mentioned above, the TE tank is still "active" if you shut off the heater supply.

The diagram also shows it at a minimum 6" distance below the top of the tank - which I take it is to prevent hot water from entering the TE tank via convection. (o.k., I googled that.) And that "other methods of controlling thermal expansion are available". I assume that refers to TE valves? Something like that would fit in the cramped heater space, but I have no drain there.

Anyway, it sounds like I'm not going to explode anything if I put it downstream of the heater, under the sink. I'll put a sign on the heater reminding me to never shut off the supply without also cutting the electricity.

Try it, monitor the pressure at the tank, see if it works. Worst case, I can always have it moved. In any event, my system should be in better shape than it's been since everything was originally installed: no TE tank, no water hammer arrestors, and the hot & cold lines switched at the heater. It's been that way for ten years now, and the failure of the original tank is the only leak I've detected - guess I should count myself lucky.

(Apologies to anyone who's offended by experimental approach to this. If the heater wasn't crammed into a tiny space, I'd insist on following the manual. As it is, I'll settle for "good enough, and not dangerous".)
 
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Jeff H Young

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meootch, it should work ok and even if you did shut the valve the likely outcome would be a little spit pout the tand p valve at worst. Im just a little technical because I dont want to get called out by inspector, homeowner or co-worker . no offence taken or meant to be given
 

meeotch

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In the photo in my original post, the flex lines connecting between the stop valve and the faucet leads are PRO8F20, described as 3/8" female compression to 3/8" male compression. I'm assuming these should not be re-used?

Based on the above, the plan with the fewest number of moving parts I could come up with is:
I've got some grey Oatey Fastape, but my understanding is that I only need it on the adapter (both sides).

If some kind soul has the patience to sanity check my choices, they will be rewarded with an effusive electronic thank-you.
 
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Sylvan

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Only once in 56 years did I have to install a ET on a 120 gallon water heater. 80 PSI is the limit NYC allows more then 80 they want a pressure reducer installed.

To much pressure can cause erosion of copper lines especially on HW and hydraulic shock with quick closing valves such as a washing machine , dishwasher as solenoid valves and automatic feeders on some boilers
 

meeotch

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Great - thanks! And yeah, finding the appropriate 1/2" to 3/4" adapter was surprisingly hard. In the end, I bought the one with the male 1/2" end, since the flex tube has female on both ends, and figured if I could avoid adding a nipple in between, I might as well do it.

Now all I've got to do is find something to use as a stand, since it'll be sitting on the floor of the sink cabinet. Again, kind of amazing that such a thing is so hard to track down. I think some of the bigger TE tanks come with them, but there's nothing for a 2 gal tank. Will probably just make something out of wood.

The orders are in. Thanks again for all the advice - fingers crossed.
 

meeotch

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Update, for anyone who is curious: got my parts this week. Turns out I only screwed up two things:
  • The original flex hose to the cold water side of the faucet was male on one end, and the replacement on my list was F-F. D'oh! Decided to move forward anyway, and re-use the old hose, despite the compression ends. (Is threaded "compression" more reusable than the type used on smooth pipe, maybe?)
  • The 3/8" to 1/2" flex hose I bought to connect the TE tank said "female straight threads" on the 1/2" end, and the 1/2" to 3/4" adapter from my list had tapered (NPT) on both ends. Again, decided to try it anyway. Female "straight" on male NPT shows no leaks, so far.
First attempt had a slight leak at the tank side of the adapter (i.e., right at the TE tank inlet, which was 3/4" NPT into 3/4" NPT adapter). I removed the adapter, noticed that some of the adapter threads were slightly chipped, and there was no rubber washer. Thanks, amazon. I didn't think NPT required washers, but bought one and jammed it in there anyway, and reinstalled.

So far, no leaks. Ran the heater down to luke warm, and checked the pressure every 10min for an hour. Never got above 60 psi. Result!

Bonus: it seems to have solved the water hammer on the cold line. Still getting it on the hot line, so a WH arrestor for the hot may be my next project, now that I've got a win under my belt. (Though still just one day in with the new install - no whammies, no whammies.)

Again, many thanks for all the info & opinions, and especially for not crapping all over an inquisitive newbie, despite the fact that the internet practically mandates it.

DSC_1944.JPG
 
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