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Estimating System Volume

Marc_19
Marc_19 Member Posts: 11
in THE MAIN WALL
I would like to estimate the total volume of my hot water heating system, because I believe my expansion tank may be too small. I'm hoping you can help me. Here is a photo of a typical radiator in my home. It measures 28"w x 23"h x 7" d. There are 24 radiators, some are smaller, some larger, but this is the average size. One of the radiators is the more traditional upright, sized 32 x 32 x 7. I haven't been able to find what radiator volume might be. There are also 24' of baseboard. I'm not sure of the piping throughout the house, but it's a rambling old four bedroom farmhouse. The boiler is a Munchkin 199K unit.

My current expansion tank is a #30. I'm considering replacing it with a larger floor mount unit to reduce the pressure swings and occasional PRV releases.

Many thanks for your help.

Comments

  • Brad White_203
    Brad White_203 Member Posts: 506
    Time and Materials

    I have a spreadsheet into which you enter the linear feet of piping per size and it will give you the volume in gallons.

    For radiators such as yours, figure about 0.07 gallons per EDR. If that radiant type is like others, (20 inches high and five inches deep), they tend to run about one EDR per linear inch. In other words, if that one is 31.5 inches long (31.5 EDR), x 0.07, that would be 2.2 gallons per radiator.

    But you know what? You can spend much less time and effort by going out to buy a couple more #30 tanks and hook them up to the same piping arrangement as your existing tank. A battery of three tanks in my experience, will serve a mid-sized house with old-style gravity HW iron piping (say 2" to 2.5" mains).

    Knowing nothing about your house, this is a punt and I should know better, but for your effort and a couple of hours time doing work you would be doing anyway, you would get the same result.

    Given that your PRV releases are sporadic, one more tank might do it. But for the cost? Put in two more for a total of three which also gives you some redundancy.

    Make sure that they connect (or the line that groups them connects) to a point just upstream of the circulator.
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