Expansion Tank - Which One?

JK60 · Dec 19, 2005

Based on many threads in this forum I would like to install an expansion tank since I do have a PRV and experience an increase in water pressure when the water heater kicks in. I have a 50 gallon gas water heater and the PRV is set to yield 50 psi of water pressure in the house. The Watts Quick Reference Selection Guide states that even their smallest expansion tank, the DET-5-M1, 2.1 gallon is suitable for my application. The next one in line is the DET-12-M1 which is a 4.5 gallon tank. I would appreciate advice in this area. Should I go with one of these two tanks or do I need to go with a larger version and why?

The local Lowe's carries a different brand of expansion tanks in 2 and 5 gallon sizes. The brand name is WellSaver. Does anyone know anything about the quality of these tanks as opposed to Watts?

Thank you,

Jerry

Gary Swart · Dec 19, 2005

While I think either would work fine for you, I think you may be crowding the upper limits of the small tank. Why not go with the large unit, it isn't much more expensive and will be adaquate if someday you decide you want a larger water heater. I used the DET 12 on my 40 gallon tank and regulate the water to 50 psi.

Sponsor · 2022-01-29T12:20:58-0800

hj · Dec 19, 2005

tank

The actual amount of expansion from any size water heater is very small, it is the pressure caused by it that is the problem, so any size tank will accomplish the desired results.

Jadnashua · Dec 19, 2005

If you set the precharge in the expansion tank to approximately the normal static pressure or maybe just slightly above, the tank itself will not normally hold any water...only a little as it expands from the heater. Then, when you open a faucet, that water will be expelled from the tank. The expansion of a 40-gallon hwh probably isn't more than a cup or so. I'd have to dig out an old physics book to look up the coefficent of expansion of water to determine a better guess.

JK60 · Dec 19, 2005

I found some information on the Watts website that states that the expansion of water from 90 deg F to 140 deg F for a 40 gallon tank is about half a gallon. So with that number in mind the smaller 2.1 gallon tank should work. But since as Gary Swart indicated the larger expansion tank does not cost much more then the smaller one so perhaps it is better to go with that one.

Another issue that I have neglected to ask about is whether anyone knows if these tanks are approved and used in California. I am asking this because the Watts tanks carry a label required by California Proposition 65 that has to do with concerns over exposure to toxic chemicals. This is the Safe Drinking Water and Toxic Enforcement Act of 1986. Watts apparently puts this label on all their products, so I was wondering if there are in fact any potential health issues associated with the installation of these tanks?

Thank you,

Jerry

Gary Swart · Dec 19, 2005

Most likely if you ate 343 of them in a 12 hour period, you might develop some form of cancer. Companies are so nervous, and rightly so, about product liability that they put warnings labels on everything. "The contents of this container (a coffee cup) may be hot", and so on and on and on...

Master Plumber Mark · Dec 19, 2005

california

nothing is safe according to california....

get the big tank, go big or stay home....

the big tank will have less stress on it compared to the little one
and its not that much more money

hj · Dec 20, 2005

tank

If you jinstall the big one, remember that if the membrane fails you will have a lot more weight to consider when it fills with water, so be sure to support it adequately.

Cass · Dec 20, 2005

If the small one works why spend the extra $$ for the big one. I don't think you will get any longer service life from the big one than the small.

Toolaholic · Dec 20, 2005

MARk IS RIGHT ABOUT CA

i live in marin co. myself! from ammandment to the usmj sf plumbing code
#EIEIO "no expansion tank shall be brought within 500 ft. of a public school
also states 'not to be used as a weapon,or branished

JK60 · Dec 20, 2005

toolaholic said:
i live in marin co. myself! from ammandment to the usmj sf plumbing code
#EIEIO "no expansion tank shall be brought within 500 ft. of a public school
also states 'not to be used as a weapon,or branished

I live in San Francisco. Would you know if the San Francisco plumbing code allows installation of an expansion tank in a single family house?

Thank you,

Jerry

Jadnashua · Dec 20, 2005

Without reading their code, I don't see how they could not allow them. There really isn't a way around not using one if the conditions dictate (such as a check valve or a prv). The system just doesn't work without one without triggering the prv in the hot water heater. Now, they may only certify certain brands/models, but there are lots of them in use across the country.

Gary Swart · Dec 20, 2005

Cass, I don't want to start a war, but the large expansion tank cost me less than $50 at HD. They didn't even have the smaller size, so I don't really know how much it would sell for, but I doubt if the savings would amount to $10. But, as HJ advises make sure it is well supported regardless of the size.

It seems to me that California has a lot of well intended regulations, but they have been dreamed up by yuppies that wouldn't know a pipe wrench from a screwdriver. There has to be provisions for dealing with closed systems because without an expansion tank in a closed system, the water heater could become bomb if the TP valve failed. The expansion tank is a viable safety device.

Toolaholic · Dec 20, 2005

jk60

had them signed off, no problem

toughest insp. in the city.

this was part of a whole house re-plumb.

Toolaholic · Dec 20, 2005

jadnashua

the city of s.f. uses the upc. in addition to that they have their own amendments to that. in addition to that you have one insp. with his own imagination

JK60 · Dec 20, 2005

I would like to thank everyone for taking the time to provide this valuable information to me. This is really a great forum!!!

Thank you,

Jerry

hj · Dec 20, 2005

[There has to be provisions for dealing with closed systems because without an expansion tank in a closed system, the water heater could become bomb if the TP valve failed. The expansion tank is a viable safety device

The expansion tank IS NOT a safety device and would not stop an explosion if the heater were to malfunction and not turn off. In fact if that were to occur, I would prefer not to have an expansion tank and would hope that the heater would rupture from the excess pressure before the temperature reached 212 degrees F.

JK60 · Dec 20, 2005

The specs on the TP on my Rheem water heater are 150 psi and 210 deg. F. Are those typical specs? I have no experience in this area, but it seems kinda high.

Expansion Tank - Which One?

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