Thermal expansion tank and vacuum breaker

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CowSki

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Hi There,

I'm installing a new hot water tank. Vacuum breakers are a code requirement in my area (as are Pressure Reducing Valves). I wanted to add a thermal expansion tank. After much discussion/research I think it is best to put it on the cold water line. BUT if the vacuum breaker is between my hot water tank and my thermal expansion tank (on the cold water line) doesn't that render my expansion tank pretty much useless?!

Thanks Guys
 

Terry

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BUT if the vacuum breaker is between my hot water tank and my thermal expansion tank (on the cold water line) doesn't that render my expansion tank pretty much useless?!

Thanks Guys

Yes. You want the expansion tank between the vacuum breaker and the water heater.
 

Terry

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Thanks for the quick reply Terry. So to confirm expansion tanks belong on the cold water line?

Yes, on the cold. They last longer that way.

watts-lfn36-instructions.jpg
 
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Clog

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Yes. You want the expansion tank between the vacuum breaker and the water heater.

This comment appears to answer the question I had in the "Vacuum Relief Valves... Revisited" thread... however, while this advice doesn't necessarily contradict, it doesn't fit in with the instructions for the Vacuum Relief Valves (linked in that thread) which do not depict the use of a thermal expansion tank, and therefore only shows the Vacuum Relief Valve attached directly to a tank tee for top water entry hot water heaters.

In that other thread, I asked about how to work in both a VRV and a TET, and how they should be plumbed in sequence, with stand offs, etc. In that thread, the consensus that I interpreted from the comments provided was that it didn't matter.

In this thread, it appears that the sequence at least does matter. But I need help understanding why.
 

Clog

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In the diagram example that Watts gives, the opposite advice appears to be given, where the vacuum breaker is plumbed between the expansion tank the water heater...

hwsupplysystem-colour.jpg


This makes me even more curious what the reasons might be for advising to do the opposite of the diagram, which is to place the expansion tank between the vacuum breaker and the water heater. Please help me understand the reasoning for this recommendation.
 

Jadnashua

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I don't think it really matters. As long as the vacuum breaker is above the tank, it should work.
 

Clog

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Terry hasn't responded, but I'm going to guess that his comment, along with that of the original poster, was more toward the idea that there should be no valve between a thermal expansion tank and the water heater.

However, the kind of valve that would disassociate the thermal expansion tank from the water heater tank would have to be a valve that closes off or constricts communication between the two, like a ball valve.

A vacuum relief valve does not cut off water flow... it only admits a little air in the presence of vacuum. And, because the relief valve itself is dead headed vertically on top of a vertically mounted tee or standpipe, not even the spring and plate that would be drawn down into the pipe could constrict the flow between heater and expansion tank, as there is no intrusion into the piping between the two.

After seeing many other illustrations of vacuum relief valve placements piped via tees or standpipes in between the water heater and the expansion tank, it is quite clear that it is ok. But in the multitude of counsel, there is wisdom, and I listen and give consideration to every voice. So when I ran across this thread and the statements made within it, I wanted to know what was exceptional about this case, versus any other.

In the absence of any clarification, it seems like it was just a misunderstanding or misapplication of generally known best practices. I'm still listening though.
 
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