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Custom Radiator

CNY Member Posts: 1
We have a one pipe steam heat, top (5th) floor apt. (total of 20 unit apts in bldg) we have removed old radiator (approx 8900 BTU) in renovation and would like to replace with different size due to the new renovations. We have our own iron workshop that can manufacture a single pipe radiator. My question is: Can we have our workshop fabricate a 5", 6" or 8" dia pipe (with pop off valve at top) that would put out the same BTU's we originally had and not cause problem with the system or banging noise?

Could you provide me with a formula to calculate the size of single pipe dia we need to achieve 8900 BTU?




  • arches
    arches Member Posts: 52
    edited September 2011
    surface area of a cylinder

    8900 BTUs is generated by 37 square feet of surface area in a steam system (240 BTU/sq ft).

    The formula for surface area of a pipe or cylinder is:

    2 pi r^2 + 2 pi r h

    So, for 8" (0.66 feet) pipe, you'd get (2 * 3.14 * 0.33ft^2) + (2 * 3.14 * 0.33ft * 1ft) or:

    2.69 sq ft or surface area for every linear foot of 8" pipe.

    You'd need 13.75 feet of 8" pipe to get the 8900 BTU.

    That's just the math...i'll leave it to the pros to comment on whether this setup would actually work (I'd guess you'd have use some sort of eccentric fitting on one side of the pipe, otherwise it would trap water and hammer a lot). Or I guess you could use an 8" elbow that reduces down to your supply pipe size (if such a thing exists).
  • Rod
    Rod Posts: 2,067
    Custom Radiator


        I must first state that I’m a home owner, not a steampro so please keep that in mind when reading this.   Interesting project- My first thoughts are that you would be much better off looking around for a used radiator that would meet you requirements. Steam radiators come in all shapes and sizes.  You would need to find one that was 8900 btus (37 sq. ft of EDR)

       Fabricating you own radiator and having it function properly would be a lot or trial and error I would think.  You might want to study the design of different types of steam radiators before deciding on a custom design of your own. You might want to get a book called “E.D.R. - Ratings for Every Darn Radiator” available in the Shop section of this website. It has dimensions and drawings of many radiators and might give you an idea of just what size you would need.

     Here are the figures you need : 1 square foot of steam radiation =240 BTUs

    so to get the equivalent of 8900 btus you would need : 8900 /240 = 37.08 sq. feet of radiation.

    Length of pipe per 1 sq ft of out side surface (see attached chart)

    5 inch pipe  = 0.629

    6 inch pipe  = 0.577

    8 inch pipe  = 0.444

    To achieve 37 sq ft of radiation you need:

    37 x 0.629 = 23 .273 ft of  5 inch pipe.

    37 x 0.577 = 21.349 ft of  6 inch pipe

    37 x 0.444 = 16.428 ft of  8 inch pipe

    (Note : This is just the outside surface area of the different size pipes and doesn’t consider/ incorporate the radiation of any connecting structures.

    Radiator vents- With steam, these are never positioned at the top of the radiator. They are usually positioned about half way up the radiator on the opposite side from the inlet pipe. Steam is lighter than air and if  the vent was positioned at the top radiator,  steam would quickly reach it and the vent would close, trapping a large amount of air which would then prevent steam from completely filling the radiator.

    Steel vs Cast Iron - Cast iron usually has a greater wall thickness which tends to act as a “heat sink” which means it takes longer to heat up and longer to cool down. This results in more even heating. In your case I imagine the boiler is producing steam continually so this may not be a problem.

    I’ve attached the chart where I got the figures for the calculations above and also a sheet showing the EDRs  of different sized radiators.  I would again try to dissuade you from fabricating you own radiator unless you are prepared to accept the project from a trial and error standpoint.

    Best of luck and please let us know how it comes out.

    - Rod
  • Jamie Hall
    Jamie Hall Member Posts: 18,923
    There's no reason

    why you can't fabricate a radiator, although for a one pipe system you will want to keep in mind where the vent should be (usually about two thirds of the way up the radiator on the side opposite the inlet/outlet).  I would suggest, though, that you might get better results if you must fabricate usinig iron pipe with fins; this will give much more surface area in much less space.

    Even better would be finding a used radiator which fits the space...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
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