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Old Boiler...leaky expansion tank

I have an old cast iron radiant heat system. There is a "Thrush #30" tank mounted horizontally between the floor joists above the furnace that start leaking badly.

My question is, do I need to replace this with another giant expansion tank or is there a more efficient, smaller (less expensive) unit that can be used in its place. I can work the pipe wrenches....

If you need the info, the house was built in the 1800's. The heat system put in sometime in the first half of 1900's. Heated square footage is about 2000 sq ft. There are 11 cast iron radiators through two floors.

Any help appreciated.


  • SWEI
    SWEI Member Posts: 7,356
    expansion tank sizing

    Depends on the volume of water in the system and the minimum/maximum temperatures and pressures during operation.  If you can post some pictures of the radiators and the piping around the boiler we should be able to help.
  • Paul48
    Paul48 Member Posts: 4,469

    have a house very similar to yours, and use a #60 Extrol. My house has an old gravity conversion with a LARGE volume of water. When we installed the new boiler, I had a #30, and it would sputter at the PRV. Went to the # 60 and no problems. It's not very big at all.
  • MisterB1965
    MisterB1965 Member Posts: 3

    I verified my requirements by using an online expansion tank calculator and the #60 Extrol was recommended. It has been ordered.

    Thanks for the replies.
  • Paul48
    Paul48 Member Posts: 4,469
    edited December 2012
    couple Things

    Put a ball valve before it. If the bladder should rupture, it's a piece of cake to change. Make sure the system is at the proper pressure.

    A. Calculate the number of feet from the regulator to the top of highest radiation.

    B. Multiply this number by 0.43 and add 3 lbs. This will give the pressure required to raise the water to the highest radiator

    and keep the system under pressure.

     Adjust the pressure in the expansion tank to match system pressure, before you install it (use a bicycle pump).
  • SWEI
    SWEI Member Posts: 7,356
    ball valve before

    and a drain valve in between, so you can check and re-fill the tank every year or so.

    Or use a Webstone Expansion Tank Pro http://www.webstonevalves.com/default.aspx?page=customer&file=customer/wecoin/customerpages/expansiontank_details.htm 
  • Paul48
    Paul48 Member Posts: 4,469

    Very cool little fitting, and a great idea.
  • MisterB1965
    MisterB1965 Member Posts: 3
    Thanks again..

    There is already a shut off before the leaky tank which I will replace due to is corroded nature. I was planning on using a valve with a drain port. Maybe a little slower but should do the trick.

    Thanks again
  • MikeG
    MikeG Member Posts: 169
    Air elimination

    Isn't it now necessary to now add some type of air elimination device to the system with this typ of expansion tank?    Mike 
  • SWEI
    SWEI Member Posts: 7,356

    I buy their Ball Drains by the case -- an improvement to the old Drain Ball, now capable of draining/purging either the main or the branch, and takes up even less space than the originals did.  They've got some pretty smart people there.
  • Jeff Perry_3
    Jeff Perry_3 Member Posts: 98
    Be careful

    how and where you mount the new #60. If the baldder in that thing ever ruptures and the tank gets water logged it will weigh about 72 pounds. Don't just hang it off a pipe. Use a bracket or something and mount it to a wall. They're supposed to be mounted vertically.

    Good luck

This discussion has been closed.