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Finding square ft. of steam coil

Ron Jr._3Ron Jr._3 Member Posts: 594
Hey , long time since I posted!

Have a problem job that I'm looking to figure out the connected load on. Steam boiler with a mix of cast iron rads and a HUGE steam coil on an ancient air handler. No ratings plates on anything for the coil. Just a little hatch I was able to peek my huge noggin into.

Is there a formula to go by to figure the square foot rating ? The coil is basically 2 ft by 4 ft. Not sure of the depth. Everything is wrapped in asbestos.

Thanks in advance for any help !

Btw the view from this home was spectacular !


  • EBEBRATT-EdEBEBRATT-Ed Member Posts: 6,945
    Without a tag on the coil or unit your guessing. But you can figure this out to be reasonalby accurate.

    You need square footage surface area of coil. L X W
    fins spacing (fins/inch)
    Number of tube running through the coil
    size of tubes running tthrough coil

    Then contact a coil mfg.and they can tell you
    Ron Jr._3
  • clammyclammy Member Posts: 2,496
    Just wondering is that a standard coil w return 90 s or is that a true steam coil that is a non freeze tube in tube stlye .I replaced one a few years ago on a ancient carrier ah and surprising enough was able to get the original Oem coil it was sitting in a-warehouse down south or like 45 years lol .amazingly at about 1/4 of having one made . I would do as Ed has stated ,was this a single pipe or 2 pipe ,If 2 don’t forget a vacuume breaker and a freeze stat if outside is ducted in . Long time no hear hope all is well Peace and good luck clammy
    R.A. Calmbacher L.L.C. HVAC
    NJ Master HVAC Lic.
    Mahwah, NJ
    Specializing in steam and hydronic heating
    Ron Jr._3
  • SteamheadSteamhead Member Posts: 13,773
    I'll say it's been too long! Good to hear from you. Still doing ship-in-a-bottle installs?

    If all else fails, go by how much EDR the supply piping can handle.

    Coming to Wetstock?
    All Steamed Up, Inc.
    "Reducing our country's energy consumption, one system at a time"
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Baltimore, MD (USA) and consulting anywhere.
    Ron Jr._3
  • Ron Jr._3Ron Jr._3 Member Posts: 594
    Hey Steamhead ! Thanks for the advice ! Yeah its definitely been a long time ! Still doing closet installs . We transitioned to doing alot of AC work. Love the mini splits. Me and my girl will be at Wetstock . We'll see you there !
  • Ron Jr._3Ron Jr._3 Member Posts: 594
    Hey clammy ! It's been a while ! Hope you been doing good. I'm not sure exactly what type of coil it is. I know its 2 pipe of course. With a trap. I'm shocked this ancient air handler is still working !
  • clammyclammy Member Posts: 2,496
    Yes it’s been a while ,from looking at the pics it’s a little hard to tell ,if each tube just runs out and just has a cap on the end then it is a non freeze tube in tube coil other wise it would have u bend .from what I have seen these types of coil work better for 2 pipe steam then a standard u bend type , .the last one I did years ago was over 40 year old ,I think when they approach 20 years they start to leak .a vacuume breaker should be installed if there any motorized valves and I would install even if there wasn’t especially if there any ducting to outside air . The last one we replaced was something like 30 x72 and I think it was rated at 750mbtu 2 1/2 inch feed .i think we got in touch w modine we had found a tag on the header w a model and serial # that coil was original w the building like 1960 maybe earlier and she had a rough life .if all else fails count the tube s there diameter lengths and the duct frame size also header dimension and supply pipe connection size .from what I ve seen and as Steamhead had stated I de also let the coils supply pipe size should also help . Peace and good luck clammy
    R.A. Calmbacher L.L.C. HVAC
    NJ Master HVAC Lic.
    Mahwah, NJ
    Specializing in steam and hydronic heating
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