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Installation and support of water heater expansion tanks.

85K views 46 replies 12 participants last post by  oh'mike 
#1 · (Edited)
Installation and mechanical support of water heater expansion tanks.

INSTALLATION AND SUPPORT OF EXPANSION TANKS - PART 1 of 2:
(Presented in 2 parts due to length restrictions of the forum.)

After doing much research in the past on water heater expansion tank installations, I'd like to share some installation procedures that might be helpful to DIY'ers who want to install one. Some procedures that I thought of are not posted anywhere else that I could find so be aware they are just my own thoughts so use them at your own discretion. Any comments or corrections are welcome.

WHY DO I NEED A WATER HEATER THERMAL EXPANSION TANK?
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See this link for an explanation:
http://www.watts.com/pages/learnAbout/thermalExpansion.asp?catId=64


WHERE TO INSTALL, AND THE ORIENTATION OF THE TANK:
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Expansion tanks can be installed anywhere in the plumbing system but that is providing that there is no shut off valve between the expansion tank and the water heater. IOW, when the shut off valve is closed, the expansion tank can still absorb excess pressure created by heating water in the heater.

Some residential expansion tanks will say that they should be installed in a hanging vertical position. But from my research, they can be installed in any orientation. Here's one website that confirms this observation:

http://www.fastwaterheater.com/expansiontanks.htm

The instructions that come with the Watts DET line of expansion tanks say that they can be installed horizontally, or vertically with the water connection on top or on the bottom of the tank.

WHAT KIND OF CONNECTION DOES AN EXPANSION TANK HAVE?
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The Watts DET-12 expansion tank has a 3/4" threaded male fitting. I believe that most if not all residential water heater expansion tanks will have this type of connection.

WHAT KIND OF EXPANSION TANK TO BUY?
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For use in a residential plumbing system, be sure to buy an expansion tank that's rated for "potable" water systems. There are expansion tanks for "non-potable" systems and I don't think folks would want to drink water from systems with a non-potable rated expansion tank.

END OF PART 1
 
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#7 ·
We always install ours whenever possible with : Brass tee on cold inlet of water heater, expansion tank threaded directly into the top of the tee, and a 4 or 6" pipe nipple in the tee to give the water heater supply room to flex around the tank and back to the valve.


There are no support issues with this installation.
 
#8 · (Edited)
We always install ours whenever possible with : Brass tee on cold inlet of water heater, expansion tank threaded directly into the top of the tee, and a 4 or 6" pipe nipple in the tee to give the water heater supply room to flex around the tank and back to the valve.

There are no support issues with this installation.
Hi Alan,

Sounds like a solid way to install an expansion tank but I'm not sure I'm picturing the installation correctly. Could you link to a picture of the kind of brass tee you use? How is the tee oriented?

Right now I'm picturing this:

Is this correct?

If yes, do you use a copper or stainless steel corrugated flex line from the 6" nipple to the shutoff valve?

Thanks for your input,
HRG
 
#2 · (Edited)
INSTALLATION AND SUPPORT OF EXPANSION TANKS - PART 2 of 2:

SUPPORTING THE EXPANSION TANK:
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This is the major point of this post. Support of expansion tanks is not covered in enough detail in my opinion. Here's why:

A new Watts DET-12, 4.5 gallon expansion tank weighs 7.8 lbs. When it's installed and working properly, some water will enter the tank but the weight will not be too excessive. However, when (not if) the internal bladder of any expansion tank fails, water can fill the tank. Water weighs about 8.34 lbs per gallon. A 4.5 gallon expansion tank will weigh 37.5 lbs + 7.8 lbs = 45.3 lbs. A 5 gallon expansion tank full of water including the weight of the tank itself will weigh 49.5 lbs. So support of an expansion tank is so very important!

VERTICAL HANGING INSTALLATION:
Just hanging a 5 gallon expansion tank from a soldered "T" fitting will be exerting about 50 lbs on the soldered connections if/when the tank fails. With the constant expansion and contraction of the pipes, fittings and solder joints because of cold water and heated water and a 50 lb weight, I believe the solder joints could fail dropping the tank and causing major flooding.


VERTICAL OVER THE COLD WATER INPUT PIPE INSTALLATION:
I've seen installations that place the expansion tank directly above the cold water input to the water heater with no other support. (See picture below) Now if the 5 gallon expansion tank gets full of water, there will be 50 lbs of weight stressing the copper pipes and fittings while they expand and contract many times a day due to cooling and heating. This could cause leaks. In addition, depending on the length of the pipe from the water heater to the tank and whether the tank is "directly centered" over the pipes, the 50 lbs of weight could cause the tank to lean on one side and possibly result in the tank falling over and breaking the water line.

HORIZONTAL INSTALLATION:
The horizontal installation is good if the tank is properly supported by a shelf or a metal strap. A failed 50 lb tank will not put stress on pipes, fittings or soldered connections and the copper pipes are free to move with contraction and expansion, unlike if the tank is installed directly over the cold water line of the tank.

THE BEST WAY TO SUPPORT AN EXPANSION TANK:
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I've come to the conclusion that the best way to support an expansion tank is to install it on a shelf with the water connector facing down, off to the side of the water heater.


This installation accomplishes the following:

1. The weight of a failed tank will be supported entirely by the shelf with no stress on any pipes, fittings or soldered connections. No chance of a 50 lb failed tank falling off like in an unsupported hanging installation.

2. With the tank and shelf installed on a wall offset from the water heater, the horizontal run of the pipe from the water heater to the tank is free to move on a daily basis due to expansion and contraction without the weight of the tank stressing things like if the tank is installed directly over and supported by the cold water input pipe to the heater.

3. *** Here's a biggie reason to have the tank installed with the water connection facing down. ***
If the water connection is facing up and the tank fails and gets full of water, it will be very difficult to remove a 50 lb tank in confined spaces. --- If the water connection is facing down, then the water can "easily" be drained out of the tank and then the tank can easily be removed.


4. *** Another biggie reason to have the tank installed with the water connection facing down. ***
In a hanging installation, if the internal bladder ruptures, the air will quickly go to the top of the tank and be expelled. Water will quickly and completely fill the tank to the brim. --- With the water connection facing down, the air will be trapped on the top of the tank and the tank can act like an air chamber hammer arrestor until the air is "gradually" depleted. This can give the home owner time to discover the rupture and replace the tank.

Note:
Since the water connection is facing down, the shelf will have to have a hole in it or two metal angle brackets could be used to support the tank. The hole in a 3/4" wooden shelf should be large enough and tapered to allow the tank to sit further down and allowing the hex nut on the fitting to be below the bottom of the shelf and thus be accessed when tightening the connection. (The convex shape of the tank at the water connection allows the hex nut to be below the shelf.)

As mentioned at the beginning, these are just my observations and thoughts in installing a water heater expansion tank. Thousands of expansion tanks are installed in the hanging position or directly above the water heater cold line but I won't do it on my home for the reasons mentioned. Over thinking the installation? Probably but that's what I always do. :)

Hope this helps some folks. I would love any comments if this helps you install your expansion tank. If you find fault with my thoughts, I'd like to hear them too to learn things that I've not thought of.

HRG
 
#3 ·
nice job
you could just use an expansion tank bracket like this one
http://www.watts.com/pages/_products_details.asp?pid=7232

also if fastwaterheater says to connect tank with a saddle valve which a saddle valve is not legal here. it makes it hard for me to agree with them on mounting and to disregard manufactures instructions and if it fails and the manufacture does not cover since it was not mounted correctly will they pay the expense
 
#4 · (Edited)
nice job
you could just use an expansion tank bracket like this one
http://www.watts.com/pages/_products_details.asp?pid=7232

also if fastwaterheater says to connect tank with a saddle valve which a saddle valve is not legal here. it makes it hard for me to agree with them on mounting and to disregard manufactures instructions and if it fails and the manufacture does not cover since it was not mounted correctly will they pay the expense
Thanks. That bracket is a really nice, easy way to support an expansion tank. Saves a lot of work building a shelf like I did. The flexible corrugated stainless steel hose makes connection to the expansion tank very easy.

EDIT: BTW, FastWaterHeater says:
***** Retail expansion tanks come with a "Saddle Fitting", which allows the installation into the system without any soldering, thereby making installation easier for the average homeowner. The saddle fitting is a device that clamps around the pipe and has female threads that will accept the expansion tank. A small hole is first drilled in the pipe, then the clamp is placed so the hole lines up with the expansion tank inlet. We do not recommend using such a fitting. They are unreliable, and allow placement of the expansion tank in the above mentioned vertical hanging position only. *****

Saddle fittings are totally out in my view.

Thanks much for the link. I'm sure it will be very helpful to everyone.
HRG
 
#5 ·
If the tank is mounted above the pipe it is attached to (open end down) then it may continue to work properly for awhile if the bladder should break. It may continue to work indefinitely if more air is added from time to time to replace the air gradualy absorbed by the water.

The only problem is if the bladder tears in a manner that it herniates into and thus blocks the pipe connection.
 
#10 ·
Hi Eplumber,

Thanks for your contribution to this thread.

I've seen that Watt's pre-charge video before. Although the narrator says to use a hand or electric pump to pre-charge the tank, he should have mentioned never to use compressed air from a service station or similar device that has compressed high air pressure.

I know that you already know this but for folks new to expansion tanks, uncontrolled high air pressure entering the tank can damage the internal bladder. Air pressure must "gradually build up" to pre-charge the tank to match the home's water pressure (but never more than 80 psi).

Thanks,
HRG
 
#13 · (Edited)
The brass tee that Alan linked to for installing an expansion tank directly above the water heater made me realize that a brass tee could be used to install a hanging expansion tank.

By not using a soldered copper tee and using a threaded brass tee instead, the tank would be "screwed" into the brass tee preventing the tank from dropping if the tank failed and got full of water. I think a metal strap needs to be installed from the brass tee to a strong upper support to prevent the copper pipes from bending down due to a failed 50 lb tank hanging from the pipes.

I still don't like an expansion tank installed with the water connection facing up because of reasons 3 & 4 in post #2, but at least using a threaded brass tee, there's no chance of soldered connections failing and dropping a heavy failed tank.

HRG
 
#21 · (Edited)
Support???

Yes, in my personal view, the horizontal method of supporting an expansion tank is good, provided that the attachment of the strap to the wall is solid. Even if the bladder fails and the tank gets full of water, the tank is supported by the strap without putting any stress on the copper pipes, fittings and solder joints. All of the copper is free to move (contract as cold water refills the water heater and expand as water is heated to the max temperature set by the user).

I've read that installing expansion tanks in the horizontal position can wet only the lower portion of the bladder and with uneven wetness of the bladder cause premature failure of the bladder. But I don't think that theory is cause for concern because of how the air bladder in the tank works.

When the tank is pre-charged before installation, the internal air bladder is pressed entirely up against the insides of the tank right up to the water input hole. IOW, the bladder is like an internal coating on the tank. When water enters the tank, it appears to me that the water will be wetting almost all of the bladder with just a very small air pocket if any.

The disadvantage of a horizontal installation is that the tank cannot be drained completely for removal if the internal bladder ruptures and the tank gets full of water.

(Oh, I just realized after typing the above that maybe your posting that picture was a tongue in cheek post for inadequate attachment of the strap to the wall. :) )

Thanks,
HRG
 
#22 · (Edited)
repairguy:

was this how you used a shelf to support yours on the horizontal installatin?

No, my installation looks like this:

Support for the horizonal shelf is by the diagonal cut sides that extend upward. There's a 3/4" vertical back piece that the sides attach to forming sort of a diagonally cut box. The 3/4" vertical back is screwed to the wall. There's a 6.5" hole in the bottom shelf that goes up 1/4" and then tapers to 9" on the top side of that shelf. This allows the convex bottom of the tank to sit on the tapered portion and allows the hex nut at the water connection to be below the bottom of the shelf. This allows complete access of the hex nut with a wrench in every direction up to the wall. Here's some detail of the shelf:
Code:
[FONT=Lucida Console] 
   ---- 3/4" vertical back piece to attach to wall.
  /
 --
|  |\
|  | \
|  |  \
|  |   \
|  |    \
|  |     \
|  |      \
|  |       \
|  |        \
|  |         \
|  |          \
|  |           \
|  |            \
|  |             \
|  |              \
|  |               \
|  | |<----9"----->|\
|  |--             --
|  |  \           /  |
|  |   |         |   | -- hole goes up 1/4" and then 
 --------------------  -- tapers to 9" at the top.
       |<--6.5"->|
|<-------12"-------->|
[/FONT]

The picture is not to scale and the angle of the diagonal is not as steep as shown. The bottom shelf is 3/4" plywood. The vertical piece that attaches to the wall is 3/4" plywood and is 11.5" high. Everything was glued and held together using nails.

Allan's method of mounting the tank on a brass tee on the cold water nipple to the heater is much simpler. However, even if I knew that when I installed our expansion tank it wouldn't have worked for us though. The company who installed our solar water heating system installed an anti-scald valve that connects the cold to the hot directly above the water heater using all copper pipes. I had to tee off above that assembly to access the cold water input to the heater.

Hope this helps,
HRG
 
#16 ·
This looks like a good way to do it. :laughing:

http://www.qriquality.com/wp-content/uploads/2010/08/Unsupported-expansion-tank.jpg



I looked through google images and I can't find any pictures of them the way we install them. I guess i'll have to take a picture of the next one I do.


On new homes we stub the cold water out a little further to the right side than where the nipple on the tank would be, that gives a little more room for a valve and a nipple and a flex supply.
 
#28 ·
For the horizontally mounted tank and strap wrapped around it, the higher above the tank the strap is fastened to the wall, the more secure the fastening is.
 
#29 · (Edited)
We put one of these in along a horizontal section of cold water pipe that branched off from the water heater feed and supplied a section of the house. It was the smaller 2.1 gallon DET-5 model, configured vertically with the outlet facing down.

Given that the most the tank could weigh when full is about 20 pounds (23.8 pounds, to be precise), we figured that strapping the tank to the wall, and supporting the horizontal 3/4 copper pipe along that same wall should be sufficient. The line going to the expansion tank does angle out from the horizontal pipe, so there is some torque on the horizontal pipe, but that is minimized by strapping the tank to the wall.
 
#30 ·
Periodic inspections of the tightness of the strap might be a good thing. I don't have a clue if this is a valid concern but am wondering if the daily expansion and contraction of the tank might loosen the strap just enough to allow the tank to slide down a bit at a time every time the tank is cooled.

HRG
 
#35 ·
Note that the amount of water that enters the expansion tank under normal operation is the same no matter where in the system the expansion tank is located.

The amount of water that enters the expansion tank depends on the size of the water heater tank and the before and after temperatures of the water inside being heated.
 
#38 ·
Note that the amount of water that enters the expansion tank under normal operation is the same no matter where in the system the expansion tank is located.
.
True. But I would think you may not want to install one on the hot water side of the water heater, because then you have 1-3 gallons of cold water in connection with your hot water line, and I'd think it would tend to cool off the hot water as it passes by, as the cold water sinks.
 
#46 ·
question on what pressure to charge tank

Hi,
i am new to the forum. I found this thread and it has been helpful. Ive got my shelf all ready for the tank install, but am getting nervous about the tank pressure.

A little background for ya: a couple of years ago the township flushed the hydrants and my water meter was damaged by some debris. I got it changed and honestly my water has never been 100% the same. I have the whistling shower heads, had a kitchen faucet leak on me and it got under my floating floor.

I tested several faucets (before the PRV change) and it the pressure was around 60 on the laundry sink (closest to the PRV).. it went down to 38 with another sink on and then 30 when the third sink was on.

after the PRV change, i am at 40 (24 hours).. but the red needle for the spike/highest level is at 90. i saw this happen before and it seemed to change when someone would use then shut another faucet off.

so my question is... do i set my tank pressure at the 40lbs? or should i adjust the prv up to about 50-55 and then set the tanks pressure at that psi?

sorry for so many questions. i am about 15 minutes from completing this job but dont want to do it with the wrong pressure setting.

Thanks!
 
#47 ·
Cueball---I suggest you start a new thread----few of the plumbers will want to read the entire thread to answer your question-----You will get the best help with a new thread in 'plumbing"

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