Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Radiator Questions

I live in an older two story home built in 1928 with hot water radiator heating.  

The system has a circulator.   I do not believe it was a gravity system as there is not a main supply line running to the high point in the house.   

The supply and return lines are both in the basement and each radiator is independently connected to the supply and return lines.  There are no radiators connected directly to another.  

Question One: There is cold water supply line that runs into a large tank (12 inch diameter by 4 feet long).   This tank is in the rafters of the basement very close to the boiler.  The cold water supply runs out of the other end of the tank and into the hot water supply pipe running from the top of the boiler.  

What is the purpose of this tank?   Is it an expansion tank?   If so, how does it work?   

It would not have a bladder like a modern expansion tank.  Is it able to just hold so much water that the size allows for the pressure to be reduced?   

Question Two:  The radiator furtherest from the boiler on the second floor of the home is different from all the rest.   All the other radiators have the supply pipe running into one side and the return pipe running out the other and going to the main return pipe in the basement.  

At the discharge end of the radiator the pipe splits and there is the return pipe that goes back through the floor.  But there is also a pipe that runs up and through the ceiling.  

The attic was never heated by radiator and was finished in the 1970s so you can’t see where this pipe goes or what it is connected too.   

There is no vent pipe running outside up through the roof.  

Did this pipe run most likely to an expansion tank in the attic that is now obscured by the finished walls?   

I am having a leak in the ceiling above this area, if there is an expansion tank above the ceiling, any chance this this could be the source of the moisture in the ceiling?   

If so, as a fix, could I just cap this pipe at the radiator or would this cause a dangerous situation where the system could over pressure?

If the tank in the basement is an expansion tank, is it necessary to have a second one?  If so could I add an additional expansion somewhere else on the system in the basement?

As another potential solution to a leaking pipe or expansion tank in the ceiling, short of opening the ceiling and making the repairs, could I add a smaller bladder expansion tank to the discharge side of the radiator and then build a new radiator cover to hide what would be an eyesore in that bedroom?

 Thanks for any help.   Pictures here:


  • fredstaple
    fredstaple Member Posts: 2
    Would this work as a solution.  Remove the large tank in the basement rafters which is close to 100 years old.   Replace with a modern bladder tanks.   

    Cap the vertical pipe at the upstairs radiator close to the radiator.  

    Could I just leave the old tank and install a bladder expansion tank between it and the boiler.    
  • bburd
    bburd Member Posts: 926
    That system almost certainly had an open expansion tank in the attic when originally installed. At some point, a more modern closed compression tank was installed in the ceiling over the boiler. You do not need two tanks, so you should be able to cut and cap that pipe that goes into the attic after draining the system water down below that level, then refill.

    Whether that old open tank is causing your ceiling leak is another question.

  • mattmia2
    mattmia2 Member Posts: 9,843
    The tank in the basement isn't 100 years old, it was added when the original boiler was replaced probably in the 50's-70's. It is mostly filled with air and the air compresses to allow the water to expand. It can become waterlogged because there is nothing to keep the water from dissolving in the water so it needs to be drained periodically. It is called a compression tank.

    The pipe to the attic probably went to or goes to an open expansion tank. You will have to go up in the attic and see if there is a tank or a capped pipe up there. If the tank is still there it could be leaking or it could overflow if the system pressure is high enough to push water above its level. It should have been capped when the compression tank was installed.

    When does the leak happen? Does it need to rain for it to leak?

    The original system was a gravity system, hot water rose out of the top of the boiler and in to the supply mains and cold water was pulled in to the bottom of the boiler because it was more dense.
  • mattmia2
    mattmia2 Member Posts: 9,843
    Oh, and someone possibly replaced the old open tank with an auto vent valve and that may have subsequently got walled in and is now leaking.
  • Jamie Hall
    Jamie Hall Member Posts: 23,554
    The one place where people really get messed up with a compression tank -- which is otherwise pretty close to bullet proof -- is when they add an air eliminator somewhere else in the piping. That does eliminate the air... which will eventually result in the compression tank waterlogging and giving pressure control issues.

    You can replace one with a bladder tank, properly sized -- but why? The best reason, honestly, is that the average modern plumber or heating guy or gal has no idea what a compression tank is or how to use it.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • PC7060
    PC7060 Member Posts: 1,204
    edited October 2022
    I think @mattmia2 has called it right, I’d open up the attic walls to find the end of that pipe.  Or cut lower down and cap off the feed. 
    @fredstaple house is the same age as my house.  Even with the significant work I’ve done on this house I didn't see signs there was ever an open air tank in attic. I did find a couple old disconnected black pipes in attic during renovations, I assumed it was part of the old gas light system but who knows, so much happens over almost 100 years. 

    Looks like original boiler was re-configured with a thrush expansion tank in ceiling paired to a the thrush air extraction valve. The valve was patented in the 30’s so not original to the house.