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Thread: Expansion Tank Change-Over

  1. #1
    DIY Junior Member ErnieS's Avatar
    Join Date
    Jan 2013

    Default Expansion Tank Change-Over

    I need some help. I have an old boiler in my 1868 brick house with the old-style steel horizontal expansion tank. The expansion tank has had it. I have patched the thing numerous times with epoxy putty but new leaks keep popping up. I would like to replace it with a bladder style tank but I am not sure where to the plumb the new tank and what changes (new valves, etc) I need to make to my system. Also, I am not sure what size bladder tank to purchase. I have looked at drawings of installations online but not sure how to relate it to my system.

    I have a hot water system with finned baseboard radiators. The house is approx 4,000 sq ft. The boiler is natural gas Peerless 256,000 btu/hr. There are multiple zones. I know the smartest thing would be to replace the whole thing but finances do not permit. I had a company come out and their quote for replacement with a high efficiency unit was over $20,000.

    To complicate things further, I have a daughter who was injured in a car accident who requires 24 hour care so keeping the system running without outages is important. We have a pellet stove and a wood stove that we use to try to avoid the natural gas bill from using the boiler but when the temperature drops too low we need to turn the boiler on. Any help would be appreciated, thanks in advance.

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  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
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    Sep 2004
    New England


    It's time to replace that ancient thing...that aside, getting one the right size is important. Check here: http://www.watts.com/pages/support/sizing_ET.asp for some help in sizing. It does require you estimate the volume of water in the beast and piping, though. Also, you need to input the starting temp and the operating temp to determine how much the water will expand and to determine the proper size of the tank.

    The tank gets installed on a T, ideally before the circulator pump - it doesn't need any valves or other controls, but you might want a valve on the branch so you can remove and replace the thing without draining the system. If you accidentally leave the valve closed, you will pop the safety overpressure valve on the boiler, since there'll be no place for the water to expand. It doesn't hurt for the expansion tank to be oversized (except for cost and locating the thing), but undersized will either wear it out faster or fail to work properly at all. Because when it does fail (they all do eventually), the thing should be properly supported so it doesn't stress the piping.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3
    In the Trades Tom Sawyer's Avatar
    Join Date
    Nov 2010


    Forget the expansion tank. Replace everything before it burns your house down
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

  4. #4
    Master Hot Water Mpls,MN BadgerBoilerMN's Avatar
    Join Date
    Mar 2011


    My esteemed colleagues are correct. This boiler is operating in an unsafe condition. There are many low-interest loans and charities available to you. Reach out.

    We specialize in condensing boilers but we recently installed a Buderus GC124 for a gal who had to get a loan to replace her 36 year old peerless boiler. You don't need an expensive boiler and I'll wager the one you have is at least a third too big for the space .

    Find a contractor that will do a heat load. Get three bids from licensed guys.

    Last edited by BadgerBoilerMN; 01-04-2013 at 04:50 AM.

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