Questions about domestic water expansion tank installation.

[DEWFPO]

Hi,

I have 2 questions regarding the above.

I need to install an expansion tank on my domestic water system.

I was planning on installing it on the cold water side of the gas fired water heater.

My street pressure is 127 lbs, knocked down to 75 psi by a Watts PRV.

I have a 50 gallon hot water heater.

Based on the charts that I have looked at, my conditions put me right at the line between needing a 2 gallon expansion tank and a 5 gallon expansion tank. Those are the only 2 sizes of domestic tanks that I have seen around here. (No 3 or 4 gallon tanks).

Question 1.) Which size tank should I go with. (in the winter, the water coming in from the street is pretty darn cold. Lots of expansion when it hits the hot water heater.

Question 2.) The fitting on the expansion tanks are ¾ inch. I have the availability to easily tap into a ¼ inch line that ran to a humidifier, or a ½ inch line. Do I need to tap into the ¾ inch main line to keep it ¾ inch all the way to the expansion tank from the water heater inlet pipe or can I use the ¼ inch or ½ inch existing lines which would be easier to use.

Thanks in advance for your thoughts and answers.

DEWFPO

 

[Jadnashua]

1. IF you go with the larger tank, the bladder won't have to deflect as much, and it MIGHT last longer. It will work just fine.
2. You could use the small line since the expansion is gradual, but it would likely be easier to anchor and attach a rigid 1/2 or 3/4" line to the tank with the proper fitting. You need to account for when the tank eventually fails...it will fill with water, and be quite heavy. Strap or put a support underneath it to account for that fact.

 

[Sponsor]

 

[DEWFPO]

1. IF you go with the larger tank, the bladder won't have to deflect as much, and it MIGHT last longer. It will work just fine.
2. You could use the small line since the expansion is gradual, but it would likely be easier to anchor and attach a rigid 1/2 or 3/4" line to the tank with the proper fitting. You need to account for when the tank eventually fails...it will fill with water, and be quite heavy. Strap or put a support underneath it to account for that fact.

Thank You, I appreciate your response. When the tanks fails, does it leak or is the bladder the problem? Is one brand of expansion tank better than another or are they all about the same?

DEWFPO

 

[Jadnashua]

Typically, the bladder springs a leak, and if you don't notice, will let water where it shouldn't be, and could eventually rust through the tank. Most people would notice their WH's T&P valve leaking since the tank couldn't do its job anymore, and realize they need a new ET (well, some people are totally clueless about plumbing).

As to brands, don't have enough experience to say one way or the other. You do want to ensure the one you buy is rated for potable water. Some are only good for hydronic heating, some can do both, and some should only be used on potable water.