Expansion tank

[hhoward]

I was thinking about installing an expansion tank on the water line in my house and would like to pose a question. I want to do it to protect my system fromthe risk of water pressure surges coming from the public service, and from the possibility of pressure building up from the water level dropping in my water heater. Should I put the expansion tank on the water main coming into the house or on the hot water line right after the water heater? I have a backflow preventer in my water heater.
Thanks!

[speedbump]

I don't see what good the tank is going to do. For one thing, a water heater can't drain unless you open the faucet at the bottom of the tank and let air in while letting water out.

I'm no plumber, but I've never heard of a backflow preventer in a water heater.

[Chris]

I think you are thinking of a pressure regulator that you have on your water heater? Homes in most cases don't have backflow preventers.

[Nailer341]

Hi Howard,
Here is an example of a standard detail or residential hot water heater with expansion tank and circulating system.
If you don't have the circulating system, just disregard that part.

[hcj]

That may be a "standard" drawing, but I see at least 8 items that would seldom be in the average water heater installation.

[Local16 Omaha]

It does show where the expansion tank would normally go. When you heat water, it expands in all directions. If you do in fact have a blackflow preventer you have created a closed system and the expanding hot water has nowhere to go. This is usually only a problem with big commercial water heaters.

[Nailer341]

Originally Posted by hcj

That may be a "standard" drawing, but I see at least 8 items that would seldom be in the average water heater installation.

do tell...

There are 27.34 ways to skin a cat, and this is one of them.
here in CA this covers the majority of the requirements for a water heater depending on its size and installation location.

I'd say it is missing more than it is showing.

It does show a good location for mounting the expansion tank which answers the question asked. Do you have anything to add to it that would help to answer the OP's question, or do you just want to tear apart a boiler plate detail?

['Cause]

Originally Posted by Nailer341

Hi Howard,
Here is an example of a standard detail or residential hot water heater with expansion tank and circulating system.
If you don't have the circulating system, just disregard that part.

Nailer, just one comment (ok, maybe two) the expansion tank on typical residence installations should be mounted in the upright position, not as shown in the detail. The reason is to not 'trap' water in the piping nor in the tank against the bladder if there is one.

[Nailer341]

Originally Posted by 'Cause

Nailer, just one comment (ok, maybe two) the expansion tank on typical residence installations should be mounted in the upright position, not as shown in the detail. The reason is to not 'trap' water in the piping nor in the tank against the bladder if there is one.

Not the watts det series.
http://www.plumbersurplus.com/pdf/02225.pdf

[SilverBack4Jack]

This is how I would answer this question in my state. State codes do vary and I do not have my current code book in front of me to quote so try not to flame me too bad.

Most homes now days have at least a non-testable residential dual check located at the water meter which in turn does cause a closed system and when water is heated and does expand. Some form of thermal expansion prevention is required in the state of South Carolina. Whether it be an expansion tank that absorbs the increase in pressure, or a shut off valve with a built in relief valve that expels the excess pressure. They even have a ballcock, or fill valve whatever you want to call it, that is designed to be installed inside a toilet tank that expels the excess pressure into the douglas valve (overflow tube) inside the toilet tank. Most people use the tank for a number of reasons.

1. Its easily indentified (doesnt accidentaly get thrown away if something goes wrong with it like a shut off valve or ballcock could)
2. It doesnt expell water (as to waste it)
3. Normally less expensive than the others

But if space is at a premium and a tank wont fit there are other options.