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General Electric Air Conditioner

I am trying to size the load of my one pipe steam system in preparation of having a new boiler installed..  I've read several of Dan's books and think I have the radiators sized.  However, part of the existing system, installed in 1939, has a GE Air Conditioner with a large "radiator" inside an air handler?  A large barrel fan (rat cage) pulls the radiant heat off the radiator and circulates it through the duct system.  I have been unable to find any information on how to size that part of the load which I believe is significant.  Any help or direction would be greatly appreciated.


  • Charlie from wmass
    Charlie from wmass Member Posts: 4,322
    Does the air handler

    have a BTU rating? Can you post a photo of it if it does not?
    Cost is what you spend , value is what you get.

    cell # 413-841-6726
  • John_b
    John_b Posts: 3
    GE AC Pictures

    I can find no rating plate.  I think the model is:  21AA3A10
  • ttekushan_3
    ttekushan_3 Member Posts: 958
    edited April 2013
    Air handler

    Air handlers like that could have been set up for general heating, or merely for reheat of chilled air or cool outdoor air. Restricted inlet pipe sizes would indicate reaheat or tempering (at least in my experience) A generously sized supply line would suggest general heat capability. A clue would be if there are sizable radiators in every room. If so, the coil is probably set up for reheat/tempering.

    The importance lies in figuring the steam consumption of that coil.

    If everything works right now, then measure the exiting air temperature of the air handler with the steam coil activated.

    Then measure the diameter of the blower, and note the horsepower of the motor. From there, we can make some inferences as to the CFM of air being moved. This all assumes that there's no rating plate of any kind.

    With specifics on CFM, inlet air temp and outlet air temp, there's a lovely formula on this site somewhere that will give you a pounds of steam per hour condensed by the coil. I should have it committed to memory, but when the mental fog rolls in, well. . .

    One other thought is that if there's a properly sized air conditioning condenser unit connected to this, then note how many tons the compressor is. You can figure about 400 CFM per ton of A/C. Then that's your blower capacity. At least close enough for boiler sizing.

    here: "CFM times Delta T (air, in degrees F) divided by 800. That gives pounds per hour steam. PPH= Sq Ft EDR divided by 4"

    as posted in this thread- http://dev.heatinghelp.com/forum-thread/75962/Steam-coils-HELP#p810357
  • John_b
    John_b Posts: 3
    GE AC

    Thanks for your reply.  When the home was designed (4500 sq. ft.), the architect felt using only radiators would create uneven heating in the large rooms.  The larger rooms, living room, dining room and three of the bedrooms on the second floor are heated with the forced hot air portion of the system.  The forced air flow also helps to circulate the radiant heat from the radiators.  When I bought the house 25 years ago, I had a new coal boiler installed.  I know there was no effort made to determine the actual load and I'd like to do things right this time.  The air handler was never connected to a chiller.  "Summer" operation drew in and circulated outside air.  I have never used that feature.  The heating portion has its own steam pipe off the main and has a wet return.  The unit also has a humidifying feature which I never used (figured out).
  • Dave in QCA
    Dave in QCA Member Posts: 1,785

    Do you perhaps have the blueprints?  Usually, if the heating system was part of the design, the radiation would all be noted in sq ft EDR.  If they did that for the radiation, they would also have done that for the air handler.  Just a thought worth looking into.
    Dave in Quad Cities, America
    Weil-McLain 680 with Riello 2-stage burner, December 2012. Firing rate=375MBH Low, 690MBH Hi.
    System = Early Dunham 2-pipe Vacuo-Vapor (inlet and outlet both at bottom of radiators) Traps are Dunham #2 rebuilt w. Barnes-Jones Cage Units, Dunham-Bush 1E, Mepco 1E, and Armstrong TS-2. All valves haveTunstall orifices sized at 8 oz.
    Current connected load EDR= 1,259 sq ft, Original system EDR = 2,100 sq ft Vaporstat, 13 oz cutout, 4 oz cutin - Temp. control Tekmar 279.
  • John Mills_5
    John Mills_5 Member Posts: 951
    We have one like that

    Been meaning to post pictures. Boiler and rads but also a gigantic air handler with hot water coil. All from the 50s. Air handler had a huge electronic air cleaner in it but abandoned. Cooling coil removed, probably had water cooled condensing unit in basement. Now has traditional A/C & coil. Control for cooling is line voltage stat in upstairs bedroom. Separate low voltage stats on main floor for heat. 1 turns on pump to hot water coil, other turns on pump for rads. We had a boiler expert in but as low as his gas bill is, he didn't feel justified in replacing the boiler now. Will post pix soon.

    We don't see the neat old jobs you guys do.
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