Expansion tanks: how big and where will it go?


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Old 02-28-07, 07:18 AM
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Expansion tanks: how big and where will it go?

I spoke to a bigbox retailer about getting a new hot water heater installed and after I got off the phone I had a question or two lingering in my head:

Where is this expansion tank they speak of supposed to go? How big is it? I googled them and they seem to come in a variety of sizes; how big of a tank will they use for a 50gal electric water heater?

The closet that holds my hot water tank isn't that big so I'm trying to imagine where they're going to put an expansion tank.
 
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Old 02-28-07, 07:27 AM
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Wrong forum...


...but Amtrol and Watts both having sizing guides if you check their web sites. If you're connected direct to the street (no valves preventing water from expanding back into the municipal supply and you are using street pressure), an expansion tank is a waste of money. Otherwise, sizing looks at capacity and total temperature rise.
 
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Old 03-06-07, 11:25 AM
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Are you on a public water supply or a private well? I agree with Who, if you're on a public water supply and do not have a pressure reducing valve or a backflow prevention device installed, then there is absolutely no need for an expansion tank, as any thermal expansion is simply going to backpressure into the public water system.
 
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Old 03-11-07, 06:24 AM
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Thanks for the information; Unfortunately - according to the installation department of my local big box retailer - code in Wake County, NC requires expansion tanks now, even though i do definitely have city water.
 
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Old 03-11-07, 03:11 PM
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Some people in the stores know what they are talking about and sometimes they say what sounds good. You will be better off talking to a local plumber and asking him/her. The issue isn't being on town water or not. The issue is if you have a back flow preventer installed. If you have a back flow installed, then as the water heats it, it won't have a place to expand and it will blow your relief valve(depending on what your water pressure was in the first place), which is why you would want a expansion tank. If there isn't a back flow preventer then the water will expand back into the street and you won't have a problem. My town recently changed to meter usage and it included a back flow preventer so a lot of customers had to install expansion tanks. Its in everyones best interest to have a back flow preventer.
 
 

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