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John97
Over The Hills And Far Away
Premium Member
join:2000-11-14
Spring Hill, FL

John97

Premium Member

[Plumbing] WH thermal expansion tank question

I am upgrading my water heater (to a larger unit). I have educated myself and completely understand the need for a thermal expansion tank on a closed system. I have municipal water, and my understanding is there is a backflow preventer (check valve) at the meter meaning I have a closed system.

My question is this:

Since the expansion tank is supposed to be connected to the cold supply - is there any real difference between a pressure tank for a well and an expansion tank. My understanding is that both are an air/water system containing a bladder/diaphragm assembly.

The reason I am asking is this: I have a brand-spanking-new fiberglass well pressure tank sitting in my garage. I bought it for the old house (which had a well). We ended up selling the place and moving before I installed it. Since I have it, I'd like to use it.

PSWired
join:2006-03-26
Annapolis, MD

1 recommendation

PSWired

Member

As far as expansion control goes, it will work just fine. However, you'll need to adjust the air pressure in the tank to slightly exceed your city water pressure in order to avoid having a large volume of stagnant water inside the tank.

John97
Over The Hills And Far Away
Premium Member
join:2000-11-14
Spring Hill, FL

John97

Premium Member

said by PSWired:

As far as expansion control goes, it will work just fine. However, you'll need to adjust the air pressure in the tank to slightly exceed your city water pressure in order to avoid having a large volume of stagnant water inside the tank.

Thanks for the reply. I understand that much.

I figured that I'd check the pressure with a gauge that screws onto an outside hose bib and then precharge the tank to a slightly higher setting.

Boooost
@optonline.net

Boooost to John97

Anon

to John97
The expansion tank can go on the hot or the cold side. But the rule is that you can't have any valves between the expansion tank and the water heater.

John97
Over The Hills And Far Away
Premium Member
join:2000-11-14
Spring Hill, FL

John97

Premium Member

said by Boooost :

The expansion tank can go on the hot or the cold side. But the rule is that you can't have any valves between the expansion tank and the water heater.

Thanks for the reply.

The install diagram for my new WH shows installation of the expansion tank on the cold side. Practically everything I've come across indicates it's best on the cold side. With that being said, that's how I am going to proceed.

I'm just going to put a tee on the cold line and attach the tank with a short piece of pipe to the tee.

tp0d
yabbazooie
Premium Member
join:2001-02-13
Bulger, PA

2 recommendations

tp0d to John97

Premium Member

to John97
I recommend setting the pressure to about 5psi lower than static (non flowing) pressure. The reason for this is- when you draw water, the pressure will drop in the house. If the tank is set above static pressure, and absorbs excess water from thermal expansion, when a draw is demanded in the house, the pressure in the tank drops rapidly, and the diaphragm inside can violently hit the tank outlet, puncturing the diaphragm. If the pressure is less than static, when the tank is full of excess water, during a demand of water, the diaphragm will be much closer to the dynamic (flowing) pressure in the system, and prevent a failure.

Tanks do lose air over time, and should be checked every 1-2yrs max. Pressure must be removed from the diaphragm while checking and recharging to get a proper reading.

Your well tank is designed to only accept cold water, and hot water could damage it. I would recommend a 8-10ft run of pipe, preferably copper, to shed heat before getting to the tank. A normal expansion tank is rated to 180F.

-j

Hawk
Premium Member
join:2003-08-25

Hawk

Premium Member

^^^ +1

enon
@verizon.net

enon to John97

Anon

to John97
said by John97:

I bought it for the old house (which had a well). We ended up selling the place and moving before I installed it.

I can't help but wonder: if the old place presumably needed a replacement pressure tank, and you were moving to a new place with city water, why did you even bring the tank with you?

Boooost
@exelisinc.com

Boooost to John97

Anon

to John97
said by John97:

The install diagram for my new WH shows installation of the expansion tank on the cold side. Practically everything I've come across indicates it's best on the cold side.

It's best on the cold side, but can go on either side.

Jack in VA
Premium Member
join:2014-07-07
North, VA

1 edit

1 recommendation

Jack in VA to John97

Premium Member

to John97
Set the pressure in the tank to the average static pressure of your system with no flow. That way the tank will "float" and any increase will be absorbed by the tank. Pre-charge should match the pressure of the system.

look at this video that explains what you need to do.

Adjusting the Pre-Charge of a Thermal Expansion Tank

John97
Over The Hills And Far Away
Premium Member
join:2000-11-14
Spring Hill, FL

John97 to enon

Premium Member

to enon
said by enon :

I can't help but wonder: if the old place presumably needed a replacement pressure tank, and you were moving to a new place with city water, why did you even bring the tank with you?

The old place didn't need a pressure tank. I had the original (to me) steel tank rust out, pop a leak, and flood the crawlspace and lower level of the house. It was replaced by another steel tank. I picked up the fiberglass tank thinking I'd put it in when I had time to prevent that from ever happening again. I planned on that being our last house. But, an out-of-state job promotion changed all that.

The new place has an irrigation well. It's been disconnected and the sprinklers connected to the city water. Everything was still there, and I thought I may want to change it back, so that's why I brought the tank with me. But, I hardly ever run the sprinklers (we're limited to one day per week watering anyway). And my water bill is so low that's it just not worth it.
John97

John97 to Jack in VA

Premium Member

to Jack in VA
Update: I am working on this today. I've got the tank in place, and most of the piping done. I'm using CPVC to go from the existing copper to the tank then back to the water heater. My cutting tool just snapped so I am heading back to Lowes. I just bought the thing yesterday.

Once I get back, I just have to finish up the piping to connect the water heater and then do the electrical connections. According to the gauge I bought, my static pressure is 80PSI for my municipal water. Is that normal?

I haven't precharged the tank yet. Tank is rated for 125 PSI max, so I don't think 80PSI would be a problem, just seems high to me though not knowing any better. Old house had a well and it was set to 40/60 on the pressure switch.

garys_2k
Premium Member
join:2004-05-07
Farmington, MI

garys_2k

Premium Member

80 psi is on the high side but not that unusual. Maybe you're closer to the pumping station or water tower. Your tank will be fine with that precharge.

robbin
Mod
join:2000-09-21
Leander, TX

robbin to John97

Mod

to John97
Here if it's 80 or higher they make you install a pressure reducing valve.

John97
Over The Hills And Far Away
Premium Member
join:2000-11-14
Spring Hill, FL

John97 to garys_2k

Premium Member

to garys_2k
Ok. Fingers crossed - I'm finished.

WH is heating up as I type. I finished the plumbing connections about 3:30 PM. I precharged the tank, double checked everything and then turned the water back on about 4:30 PM. Wife picked up pizza so I took a dinner break. After dinner, I checked everything over again, did the electrical connections and flipped the breaker.

I know I've posted about this before, but let me wrap it all up. This wasn't a typical WH replacement. My house originally had two 38-gallon lowboy electric units in different locations, each supplying a couple bathrooms, one supplied the kitchen, the other the laundry, etc.

Both units were sitting on corner shelves in their respective locations. The one in our laundry room supplies the master bath. Problem is, it couldn't supply enough hot water for the big-ass jetted tub. I have no idea how the previous owners ever used this thing (which they claimed they did). I guess they liked cold baths. Anyway, I replaced this unit with an 80 gallon A.O. Smith Voltex hybrid unit which is now located in the garage. The shelf it was sitting on has been demolished, which will allow us to stack our washer and dryer, giving us more space. But, I've got to deal with the cold water shutoff issue that's being discussed in my other thread.

The other WH is located in a utility/storage room at the other end of the house. It was 2002 vintage. The one I pulled out of the laundry room was 2012 vintage, as it was installed the first month after I bought the place (replacement through home warranty). I removed the 2002 vintage WH and replaced it with the 2012 vintage unit. The WH is now on the floor beneath the shelf. The pressure tank is now on the shelf, in the space formerly occupied by the water heater. I transitioned from the copper cold water line to CPVC to connect the tank and from the tank down to the WH. There's about 8 feet of piping between the tank and the WH.

I'm glad I got this done when I did. The old 2002 WH looks like it was on borrowed time.

The pressure tank is a 20-gallon unit, so it should be more than enough to cover any thermal expansion generated by the water heaters.

garys_2k
Premium Member
join:2004-05-07
Farmington, MI

garys_2k

Premium Member

Sounds good, and yeah, definitely not a typical WH swap.