Expantion tank?


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Old 04-06-08, 11:57 AM
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Expantion tank?

I perchaused a new water heater today to replace my old one. I am just woundering about the expansion ank on the cold side of the heater. Do I need replace the Expansion tank also, or is there any thing that i need to know when swappong tanks over.

Thanks for the help,

John
 
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Old 04-06-08, 12:15 PM
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The expansion tank will go on the hot water outlet side of the water heater on a tee, not the cold. If you have one already in place, no need to replace it unless you have problems with pressure spikes.
 
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Old 04-06-08, 03:39 PM
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Maybe Chandler has seen different expansion tanks than I. I have never seen, or heard of, a domestic water heater expansion tank installed on the hot water outlet piping.

In my area the expansion tanks are ALWAYS installed on the cold water piping, after the shut-off valve feeding the water heater.
 
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Old 04-06-08, 07:28 PM
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Maybe, but to harness the expansion of the hot water, it seems it should be on the hot water outlet side rather than on the cold water dip tube side, where no water will expand. Interesting point, but I believe you are right, the manufacturers place it on the inlet side.
 
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Old 04-06-08, 07:58 PM
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Before the days of installing check valves on water meters the hot water could back up all the way to the municipal main in the street.

Even today it is not uncommon to find the cold water feed to the heater warm some distance back from the water heater. In other words, the pressure is the same at all times on either the inlet or the outlet of the heater. That is why you can install a pressure gauge anywhere on a cold water line to see the effect of the expanding water (rising pressure) from heating the water.

Really, you could put the expansion tank ANYWHERE on the cold water piping and it would do its job. The rule to put it between the cold water shutoff to the heater and the heater itself is so that the heater is still protected if the shutoff valve is inadvertently closed while the heat source is still energized.
 
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Old 04-07-08, 04:17 AM
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Using that physics theory, wouldn't it still work on the hot water side as well? It would seem expansion is expansion, and where it occurs isn't important as long as the pressure is taken off the tank itself. Water is expanding in both directions. Just wondering.
 
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Old 04-07-08, 08:08 AM
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So in conclusion, I dont have to replace the tank, and it is fine on the cold water side.
 
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Old 04-07-08, 10:17 AM
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To answer the OP, you can reuse the tank and yes, place it on the cold side.

I think the point of putting it on the cold side is to protect the internal bladder of the tank from the high temps of the heated water.
 
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Old 04-07-08, 11:11 AM
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Wink

If the tank is still good use it. Ill go for on the cold water line also.
 
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Old 04-07-08, 05:31 PM
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Originally Posted by Ed Imeduc
If the tank is still good use it. Ill go for on the cold water line also.
how know if it's bad?
 
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Old 04-07-08, 08:09 PM
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You need to connect a pressure gauge to your piping. The big box stores sell a gauge that has a hose connection and a resettable highest reading hand for about $10. You connect it to any hose bib that is piped downstream of the pressure regulating valve (PRV) on the main pipe feeding the house.

Most people try it on an outside hose bib but sometimes the outside faucets are piped ahead of the PRV to give higher pressure on the garden hose.

Laundry connections are ideal for the gauge. Of course you have to open the valve after attaching the gauge. Leave it on over night and check the highest reading. If it stays about the same overnight you're probably okay.

A more definitive test would be to check the air pressure in the bladder of the expansion tank when it is disconnected from the piping. The air pressure should be the same as the nominal pressure of your water system. Use a tire pressure gauge on the expansion tank. If you get water from the tire valve the tank is definitely shot.
 
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Old 04-08-08, 04:13 AM
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Pendragon, now that blows my theory out of the "water", but it makes even better sense. The hot water would have adverse affects on the bladder.
 
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Old 04-09-08, 07:05 PM
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Thanks a bunch guys, you have been great. I assume that the "Big Box Store" is the one with the Orange sign, not a store acually names the big store.
 
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Old 04-09-08, 08:25 PM
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The "big box" store with the orange sign has three words in its name. There is another big box store that has a blue sign of only one word. And depending on where you live there may be a third big box that has a name starting with an M.
 
 

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