Do You Need More Then 1 Expansion Tank

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cloves

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Hi everyone,

We recently swapped to an AO Smith Vertex to provide our domestic water supply and to provide our hot water for our radiant system (closed system). Currently the domestic supply line comes into our water filters 2 stage and then to an expansion tank before "Teeing" into the vertex cold supply line and the cold side of a mixing valve.

Now my question is, my radiant heat guy has an expansion tank in his diagram. Do I also need to have an expansion tank on the radiant side of the system? Wouldn't the expansion tank going into the cold supply of the water heater suffice?

I added the expansion tank on the right to the original drawing. My radiant guy says I need both but I can't wrap why.
 
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hj

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The two systems are completely separate, operate at different pressures and temperatures, and glycol has a different rate of expansion than water, so YES you do need two tanks.
 

cloves

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AO Smith Vertex Sample of Piping Expansion Tank - IMAG1294.jpg


Thanks HJ. The system will actually be using water an not glycol. I am using a Vertex as the water supply for both domestic and the heating system. Heat exchanger will be used for the heat side.

Still a little cloudy as to why I would need 2 expansion tanks on a closed system. Wouldn't all the expansion of water take place near the water heater? If that is the case wouldn't the expansion tank on the left hand side which is the supply line take care of the expansion?

Mind you the the illustration is a little incorrect. The blue cold supply comes in at the top of tank. Before cold water enters the water heater, it passes the expansion tank before "Teeing" off to the tanks supply and the other side of the mixing valve.

Above is the real world picture of what I have so far.
 
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cloves

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Here is an example of what the system will look like when complete. Here there is an expansion tank by the cold return as shown in the plan.

Radiant Heat Manifold & Vertex Water Heater - imgp8249.jpg
 

hj

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SInce you are using a heat exchanger for the heat side, it is a "closed system" and NOT connected to the domestic hot water, therefore, and since it will probably be operating at a much lower pressure it needs it own expansion tank.
 
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