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Estimating the volume of water in radiators

Shahrdad
Shahrdad Member Posts: 120
I have been looking for a way to estimate volume of water in my 1890s cast iron radiators. Most of them are 38 inches tall, 9 inches wide, and have three columns. I also have three rads with four columns that are 44 inches tall and 11 inches wide. Total EDR all for the radiators is 1,414 Sq Feet.

Looking through the archives, I saw a couple of old post where someone suggested that for this type of rads, there is approximately 0.07 gallons per Sq foot of EDR, which makes the water content of my radiators around 99 gallons. Another thread gave a formula of 1.5 pints per sq foot of EDR for column rads, which gives me 2,121 pints. 2,121 pingx / 8 pints per gallon = 265 gallons. The two results aren't even close.

What rule of thumb do you use to estimate the volume in old radiators?

Thanks!

S.

Comments

  • Jamie Hall
    Jamie Hall Member Posts: 23,170
    I presume this is for estimating the total water volume for a hot water system? Since for steam the internal volume is irrelevant...

    The problem is that the internal volume will be remarkably different for different designs.

    Can you disconnect the radiators from the system? And do they have a bleeder? If so -- no problem. Disconnect the radiator and cap one end. Connect a hose to the other end in some ingenious manner. Open the bleeder. Fill the radiator with water. Get a bucket or other measuring device and empty the radiator into the bucket with the hose...

    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Shahrdad
    Shahrdad Member Posts: 120
    It's for the radiators, which I wasn't planning on disconnecting.
  • Starting with a cold system, you could turn off the radiator that you're working on and get the system nice and hot. Turn the system off and do the reverse: turn off all the other radiators and open the one you want, to measure the time it takes for hot water to leave the radiator after you turn the system on again. Chart the duty point of your pump and you will arrive at a GPM that you can multiply by the time it takes for hot water to circuit the radiator.

    :)
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
  • DanHolohan
    DanHolohan Member, Moderator, Administrator Posts: 16,513
    I don’t have access to it now, but B&G has a technical booklet called Air Control in Hydronic Systems. Gil Carlson wrote it. He included a chart for estimating radiator volume, based on system Btuh load. 
    Retired and loving it.
    kcopp
  • Shahrdad
    Shahrdad Member Posts: 120
    edited March 2021

    I don’t have access to it now, but B&G has a technical booklet called Air Control in Hydronic Systems. Gil Carlson wrote it. He included a chart for estimating radiator volume based on system Btuh load. 

    Thanks Dan. Maybe I can find a version of it on line.

    S.
  • bburd
    bburd Member Posts: 909
    edited March 2021
    There must be radiator volume charts because that’s how we size expansion tanks: system water volume.

    Bburd
  • DanHolohan
    DanHolohan Member, Moderator, Administrator Posts: 16,513
    @bburd that’s exactly what’s in the booklet I mentioned. I just don’t have it with me. 
    Retired and loving it.
  • bburd
    bburd Member Posts: 909
    @DanHolohan The part that confused me about your message was that the water volume is “based on system Btuh load”. And radiation type, I assume.

    Bburd
  • DanHolohan
    DanHolohan Member, Moderator, Administrator Posts: 16,513
    @bburd As I recall, it gave two types of older radiators (thin-tube, column), baseboard, convectors, and then related this to Btuh so you could get a cumulative average volume for the whole system. I think piping was included in that chart. Wish I had it here. It was very easy to use when sizing compression tanks.
    Retired and loving it.
  • DanHolohan
    DanHolohan Member, Moderator, Administrator Posts: 16,513
    edited March 2021
  • Shahrdad
    Shahrdad Member Posts: 120
    edited March 2021

    Found it! Look on pages 41 and 42.

    Thank you Dan. I've been learning about compression tanks, and sizing them simply by BTUs without considering the volume of water in the pipes and radiators didn't make a lot of sense to me. This is great.

    S.
  • DanHolohan
    DanHolohan Member, Moderator, Administrator Posts: 16,513
    Happy to help!
    Retired and loving it.