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Running two oil burners from a single thermostat

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I recently purchased a new (old) house that has two separate oil burners that feed a common plenum. I believe the furnaces originally had a twinning unit that was likely damaged in a basement flood. My havac tech tells me that a replacement twinning unit is not available. As a work around, each furnace is controlled by separate thermostats located next to each other. I'd like to find a way to run both furnaces off a single controller. Is there a thermostat available that can accept a set of wires from each furnace? If not, is there another economical solution to my problem. ThNks in advance for any suggestions.

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  • GW
    GW Member Posts: 4,699
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    He says twinning is no longer available? I think they are.

    Yes you can use one stat but you'll need a relay, your one stat can call both furnace. May need a transformer too. We use the RIB relays they are great
    Gary Wilson
    Wilson Services, Inc
    Northampton, MA
    gary@wilsonph.com
    Solid_Fuel_Man
  • STEVEusaPA
    STEVEusaPA Member Posts: 6,505
    edited March 2017
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    Also if they were twinned, that would indicate to me that maybe both don't need to run at the same time, and they were staged-One furnace shoulder seasons, mild weather, 2 furnaces as you approach design temp. They're are plenty of controls to do this.
    Maybe the easiest way is to get a 2 stage t-stat, and make one furnace emergency heat. The downside to this is that they won't rotate and one furnace would work harder than the other.
    https://customer.honeywell.com/resources/techlit/TechLitDocuments/69-0000s/69-1387.pdf

    There was an error rendering this rich post.

    Solid_Fuel_Man
  • GW
    GW Member Posts: 4,699
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    I have never installed a two-furnace application, but I really think you need a twinned system.

    I was just looking at my Lennox price book and all of the upper end systems have bold print "Can Not Be Twinned!"

    The more basic furnaces say "Twinning Capability"

    I presume all the manufactures would be similar
    Gary Wilson
    Wilson Services, Inc
    Northampton, MA
    gary@wilsonph.com
  • hvacfreak2
    hvacfreak2 Member Posts: 500
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    Here is a possible lead -lag solution. I believe these are relatively inexpensive.

    icmcontrols.com/LEAD-LAG-CONTROLS-Prodlist.html
    hvacfreak

    Mechanical Enthusiast

    Burnham MST 396 , 60 oz gauge , Tigerloop , Firomatic Check Valve , Mcdonnell Miller 67 lwco , Danfoss RA2k TRV's

    Easyio FG20 Controller

  • GW
    GW Member Posts: 4,699
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    not sure you want two furnaces on the same duct system w/o twinning through---you'd need some back flow dampers installed.
    Gary Wilson
    Wilson Services, Inc
    Northampton, MA
    gary@wilsonph.com
  • hvacfreak2
    hvacfreak2 Member Posts: 500
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    GW said:

    not sure you want two furnaces on the same duct system w/o twinning through---you'd need some back flow dampers installed.

    Or at least run both fans together. On low speed this may be do-able. My ac system is twinned and my fans run together , but they are pretty small at 018 each.

    hvacfreak

    Mechanical Enthusiast

    Burnham MST 396 , 60 oz gauge , Tigerloop , Firomatic Check Valve , Mcdonnell Miller 67 lwco , Danfoss RA2k TRV's

    Easyio FG20 Controller

  • JUGHNE
    JUGHNE Member Posts: 11,074
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    I did see a double set of twins sharing common supply and return. 1 T-stat would call for heat, 2 burners come on, the other 2 had outdoor T-stat to keep them off most of the time.
    These were NG with the old fan/limit control. Temp rise would start the fan for each burner. There was a sail switch that would turn on the fan for it's twin. The fan control must have been adjusted to get the on temp for the lead twin close to the other lead twin.

    A reason today to not twin high end furnaces is the variable speed blower motor. They may both start together but would have a tug of war back and forth wanting the air...from what I have been told.
  • John Mills_5
    John Mills_5 Member Posts: 952
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    Twinning kits are made. Any contractor can get one. Staging makes the most sense. Need 2 stage stat and wire W2 from the board to the 2nd furnace. Can alternate by switching wires to give equal run time.

    https://jacksonsystems.com/products/jackson-systems-universal-twinningparalleling-kit.html
  • midcenturyreno
    midcenturyreno Member Posts: 2
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    Thanks to all for your input.