Do I need an expansion tank???

[TAHUSKER]

We have been in our new house for about a year (11 yr old house, but new to us) and I was talking with a neighbor the other day. He told me his horror story about how his water heater busted and "flooded" his basement a couple years ago. He is telling me that the neighborhood's main lines have a valve that prevents water pressure from going back out to the public supply--and that this caused his water heater to rupture. Thus . . . he is telling me that I need to have an expansion tank installed before it's too late.

I have never heard of this before. Isn't this what the pressure/temp relief valve is for on a water heater??? The pressure goes beyond a certain level and it lets some off?

Anyway, I guess I am wondering if I need the expansion tank. My water heater is only 2 years old (I have the receipt from the previous owner) so I have to think that maybe the neighbor's was older and just gave out. But any opinions/suggestions would be welcomed.

If I do need an expansion tank, is that a DIY job?

Thanks!

[HayZee518]

never heard of a pressure relief device for the input to a hot water heater. an overtemp/over pressure device yes. it screws into the top of the heater and when it opens dumps water on the floor or to a drain.

[596]

The TP relief valve should protect the tank, so that was probably not what caused your neighbors tank to leak. I tank can be damaged by pressure in excess of 150, but it would take considerably more than that to actually cause a rupture.

But the TP should not be used to take care of a normal daily situation involving water expansion when the burner runs, and street pressure is high, or you have a non-bypass PRV.

Todays water heaters more often than not need an expansion tank

[LazyPup]

In any installation where the supply static pressure exceeds 85psig or where it may have occassional pressure spikes in excess of 85psig we are required to install a PRV (pressure reducing valve) to limit the line pressure to not more than 85psig.

Water reaches maximum density at 39degF and when heated or cooled from that temperature it expands. By example, when water freezes it expands approximately 10% by volume which esplains why a frozen pipe will burst. On the other hand as the water in the water heater is heated from the incoming cold temperture it also expands by volume. In its liquid state water will expand approximately 10% until if flashes to steam. Saturated steam expands to 1728 times the liquid volume of the water.

Under normal circumstances when the water in the water heater expands the volume can be absorbed by some of the water in the cold water piping backflowing back to the municipal main, however, when a PRV is installed it has the same effect as installing a backflow preventer (check valve) in the cold water line. This means that the system cannot release excess volume by backflowing to the municipal main so the Plumbing Codes require that when a PRV is installed we must also install an expansion tank on the water heater cold water supply line.

[TAHUSKER]

Are the expansion tanks fairly straightforward to install for a do-it-yourselfer? I have seen them for $50 or $60 online and it looks like a pretty simple installation.

I would hate to pay the $$ for a plumber to do this if it's not too difficult.

[HayZee518]

in the horizontal run to the cold water supply, install a T fitting. the tank screws into the bottom leg of the T.

[TAHUSKER]

Any recommendations on what size tank would be needed for a 50 gal water heater?

[596]

In a typical home store or plumbing supply, they will stock 2 common sizes, about 2 or 2½ Gal, and about 4 gal. There is a chart on the box showing the gallon and BTU arrangements.

[TAHUSKER]

Thanks for the help, everyone!

[ramoncb]

I have just replaced the expansion tank on the cold water line to the water heater. I have followed the recommended size and capacity, but I still measure as high as 120 psi on the house pipes. It should be 80psi or lower! Am I missing something here?

[LazyPup]

Ramoncb...you question is slightly off topic for this thread but i felt the question was important enough that i have moved it to a separate thread under the heading "Water Pressure Too High"