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Expansion tank sizing

samstusamstu Member Posts: 1
edited August 12 in Gas Heating
Hey everyone. Replacing an old Weil-McLain with a Burnham Series 2 299k BTU (input).
There are 6 loops going to 6 apartments (Building size is approximately 5,800 Sq Ft).
-It is a baseboard heating system

The heating contractor has ordered an Amtrol Extrol SX-60V expansion tank (32 gallon tank volume) to use on the system (floor standing).
Reading the literature on Amtrol's website (link below), it appears that this model is grossly oversized.
However, when I pointed this out to him, he insisted that it's what my system needs.
So I turn to you: Is there any way that a 299k boiler would need such a large expansion tank?

Here is a link to the Amtrol sizing chart:

Amtrol Extrol Specification details:

And if it is too big, will that cause any problems? Is it worth arguing over or should I just let it go?

Thank you!


  • hot rodhot rod Member Posts: 7,059
    Is it an old iron pipe system? The sizing has a bit to do with the total system volume.

    Certainly no issue with over-sizing, other than cost.

    Maybe he had one sitting around in his shop :)
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • EBEBRATT-EdEBEBRATT-Ed Member Posts: 2,466
    The only way to size a tank correctly is to know the water volume in the system . Two ways to do this:
    1. calculate the water volume in the boiler and the pipe fittings and baseboard.
    2. Drain the system and the fill and vent it using a water meter to read the water volume.
    3. 3 Guess

    As @hot rod said oversizing (in this case) will not be a problem other than cost
  • lchmblchmb Member Posts: 2,512
    and if you guess make it bigger...;)
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