Expansion tank

Is it mandatory that an expansion tank is installed on a water heater>?
I do not have one , things seem to be fine...no leaking from relief valve..
If I must have one, I will put one on, but if not then I will save the expense.
thank you in advance for your advice.
fishman

http://www.watts.com/pro/divisions/watersafety_flowcontrol/learnabout/learnabout_thermexpansion.asp

tank

It is only advisable when you have created a closed system where thermal expansion as water is heated in the water heater causes extreme pressure buildup.

Just to carry HJ's answer a bit further. A closed system results when you have a pressure regulator valve or if you water meter has a check valve built in. Basically, when you have either of those, when the water heater heats water the water expands. In an open system (one without the PRV or check valve) this expansion is absorbed by the city water main. In a closed system, this expansion has no place to go so the pressure rises quite dramatically until it trips the T/P valve on the water heater. So if you have a closed system, you need an expansion tank to absorb this expanded water pressure. Since you are apparently are not experiencing any problems with the T/P valve tripping, I think you an assume you do not have a closed system.

I always say... If it works, don't fix it!

Not always

And I always say that, "Moen valves and garbage disposers will keep working long past the time when they should be repaired or replaced".

Gary Swart said:

Just to carry HJ's answer a bit further. A closed system results when you have a pressure regulator valve or if you water meter has a check valve built in. Basically, when you have either of those, when the water heater heats water the water expands. In an open system (one without the PRV or check valve) this expansion is absorbed by the city water main. In a closed system, this expansion has no place to go so the pressure rises quite dramatically until it trips the T/P valve on the water heater. So if you have a closed system, you need an expansion tank to absorb this expanded water pressure. Since you are apparently are not experiencing any problems with the T/P valve tripping, I think you an assume you do not have a closed system.

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Gary,

Would you mind taking this answer a little further? Is is because water should not run backwards through a pressure regulator (damaging it?) that systems with regulators are closed? Or is there some other reason? Do you know if open systems are becoming more obsolete because water districts don't want to take the chance of water coming back into the street and contaminating city water?

Thanks, Chris

I can't answer the question of why water does not flow back through a PRV with anything learned or profound. All I can say is that they are made that way, probably for a reason. I doubt that many cities are becoming very concerned about open systems contaminating their water supply, but there may be some since at least some new meters have a check valve although I can't say for sure that contamination prevention is the reason for that. I can tell you that there is a very real contamination potential that is ignored by many cities, and that is when lawn irrigation systems use domestic water without backflow prevention requirements. Some require a device be installed but don't require annual recertification, so there are bound to be many devices that have failed and are not detected and repaired. And, they do wear and fail. Mine required new plungers when it was inspected this spring because it wouldn't hold the prescribed pressure. But, that's a different war than your original question.

If a PRV had easy two-way water flow, it couldn't reduce the pressure! But, some of them will allow water to flow back IF the internal pressure exceeds the external pressure.

Some PRV's have a built in bypass (Watts U5B w/by-pass, for example) which are designed to allow high pressure created by hot water expansion to migrate back through the PRV and into the city main. However, if the city main pressure is also really high (the reason for the PRV in the first place), like in the middle of the night when no one is using any water, hot water expansion may be trapped in the domestic system. Such is a case of an open system where an expansion tank would be advised.

I checked the pressure at the tank, its approx. 40lbs at the drain valve with the tank up to temp.
I have no weird banging , clanging, vibrating, groaning or any other strange sounding pipes.
No leakage at the relief valve on the tank.
I have the water at, according to my meat therm, 123F. Seems plenty hot enough for me, and it will give four quick showers in a row with no problem.
Actually there are six of us, female 14 year old, massive hot water user!...and at this point we have yet to run out of hot water. Used to heat with a oil fired boiler-iron radiator system...hot water from the boiler as well...now its all nat. gas..fuel oil here lock in pricing for the2008-2009 season is $6.50 per gal for #2 fuel oil...
Any way off topic there for a minute...
I am of the mind to leave it as is for now and unless there are problems I wont mess with it...the system is as far as I understand, closed as there is a pressure regulator valve on the line coming in the house.
From past experience I am really reluctant to mess with things that are not really broken..
Does a watch and see approach make sense at this point or should I just install the expansion tank anyway?
thanks
fishman

You don't have a closed system. You do not need an expansion tank.

hj said:

And I always say that, "Moen valves and garbage disposers will keep working long past the time when they should be repaired or replaced".

Click to expand...

That is a good one, hj! I had never heard anyone say it just that way, but it is so, so true!