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twinning furnces

what does it take to twin warm air furnaces? is it just tying the tstat wires together or does it also mean tying the ductwork together suply and return anyone have any pictures or diagrams


  • clammy
    clammy Member Posts: 3,111
    twinning kits

    Ed it has been a few years since i've twinned units together ,but when i was there where twinning kits avaiable from carrier and byrant which tie all controls together and cycle the units burners and fan to run together,usually we would sit the units on a base so we could pull return from the bottom [mimium 10 inch high} we also would tie the supplies together also and usually use 2 smaller coils and 2 condenser unit for the a/c and some times set up the cooling end as 2 stage .it's really ashane that larger hot air furnaces are not around any more good luck clammy
    R.A. Calmbacher L.L.C. HVAC
    NJ Master HVAC Lic.
    Mahwah, NJ
    Specializing in steam and hydronic heating
  • John Mills_4
    John Mills_4 Member Posts: 43

    modern furnaces have twinning as a function of their boards. I like to stage them with 2 stage heat and if 2 cooling units involved, 2 stage cool. Be sure furnaces are identical size & blower. No variable speed motors.
  • Empire_2
    Empire_2 Member Posts: 2,343
    Her is a Job that is twinned...

    AT the time, this was an incomplete job.

    MIke T.
  • Wayne_28
    Wayne_28 Member Posts: 8

    Twinning 2 or more furnaces together is a way to achieve a larger heating or cooling capacity.

    The purpose of twinning terminal is to start the indoor fan motor(s) at the same time. If one motor is energized and the second one is allowed to spin free, the air flow across the unpowered motor will be reverse. Once the second motor has electrical power applied, the motor will continue to run in the reverse direction. On commercial refrigeration condensing units, the condenser fan motors have the initial start capacity to overcome the the reverse flow and spin correctly. Fan motors used in furnaces do not have this capicity.

    Most of the new control boards have a twinning option, screw terminals to energize both fans at the same time. Some of the retrofit boards for Trane and Rheem required both control boards to be replaced at the same time, if the replacement board was not the same manufacture/part number.
  • ed wallace
    ed wallace Member Posts: 1,613
    twinning furnaces

    is it possible to have separate returns and supply ducts and run both furnaces off of 1 tsat
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