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Stat wiring

Ex Maine Doug
Ex Maine Doug Member Posts: 162
<strong><span style="color:#880000">I have a Honeywell stat model RTH 2300B1012, a typical digital heat/cool simple programmable.  I would like to use the one stat to run the AC as well as the steam boiler for winter heat.  It would be preferred to use the 24vac from the AC unit for the gas valve and disconnect the 120vac power to the boiler transformer. Simplify and reduce one more breaker.

The AC is cool only so would be just sitting during the winter and the circuit is 3 wire for AC on and fan on (or auto),  Seems like I could use the 2 conductor heat circuit for the boiler.  The boiler of course has an LWCO and has a spark pilot ignition system.  Have not opened the boiler junction box to see how the ignition circuit is wired.   

Sound doable or should I just use the heat contact in the same stat powered by the boiler transformer?,</span></strong>


  • mjcromp
    mjcromp Member Posts: 57

    if I got this right. You will need more than 3 wires. you can run it from your ac unit. R,Y,C,G and be fine on the ac side. For heat you can hook up 2 wires W and C to a relay to power the coil side of the relay. use the dry side for your boiler TT contacts.
    Too bad common sense isn't very common.
  • JStar
    JStar Member Posts: 2,752
    Personally... sounds complicated and harder to troubleshoot if you have a future problem. Sure, you might be able to do it, but why? You don't gain anything from it. Plus, each piece of equipment should have its own dedicated breaker.
  • Ex Maine Doug
    Ex Maine Doug Member Posts: 162
    I have run

    5 conductor stat lines to the two stats, one on second floor and one one first floor for the new AC units.. The Honeywell on the first floor has been controlling the steamer, I replaced the "round one" last winter when All Steamed Up Inc. was in to tune, balance, silence and make it right.

    The steamer has a 1 inch BX line from the panel to a 4 inch j-box to pipe to the 24vac TX. A mess left years ago. So we have a 15 amp breaker to feed a 24vac circuit. Aside from an internal dead short in the antique TX, I don't see the breaker and messy original wiring doing much if I can pick up the 24v from a source not being used in the winter and already fused and on its own breaker. Adding a relay is not an issue, there is plenty of space in the air handler wiring box.

      JStar, I can see the advantage for someone coming in to troubleshoot to have them separate circuits.  My place in Maine has 6 zone radiant floor, towel heater on constant circ, VSI, outdoor reset. Dual boiler staged, Pri/Sec with E44 Ergo in Pri circuit to up water content and indirect DHW. Main floor with 2 zones of panel rads. All under Tekmar controls.   The local P & H Co. that installed the hardware had no clue how it would operate. I am still working on that one playing with controls and methods, a grand experiment according to my wife. I have overheard her say "expensive toy" a few times. 
  • Steamhead
    Steamhead Member Posts: 14,459
    Doug, I agree with Jstar

    each appliance needs its own circuit. I believe that is also a Code requirement, though I'd have to look it up to give you chapter and verse.

    When you replace that boiler, you'll want a power-burner unit for best efficiency. These need a 120-volt feed so the A/C transformer wouldn't do any good. I'd leave the thermostat circuits separate, it will avoid future complications.
    All Steamed Up, Inc.
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
  • Ron Jr._3
    Ron Jr._3 Member Posts: 603
    edited July 2010
    Why use the one transformer ?

    I'd think the simpler route would to keep the AC and heating circuits separate .  

    We combine heating and cooling in one thermostat from time to time . Just gotta make sure the wire is low voltage ( only seen one gas steamer wired in line voltage to the T stat , so it ain't a problem ) and your thermostat has separate RC-RH terminals . The jumper HAS to be taken out between those 2 terminals , then you can wire the steam thermostat to RH and W .  

    Personally , I'd rather have 2 separate T stats . Just my preference .
  • Techman
    Techman Member Posts: 2,144
    Tstats or Tstat

    I do service only and have seen many wiring ways.You can do two seperate Tstats if you like.You can do one Tstat if you like.Using one stat,you'd be better off not crisscrossing the low volt circuits. Use Rc ,Y,G, for the cooling an Rh,W for the heat. The cooling xformer MIGHT NOT have enough VA 's to feed the heating controls ,relays etc.Your choice,you pick. But having a wiring diagram on hand would help the next mechanic just a little.The tstat you have was purchased from a "big box " store?
  • Ex Maine Doug
    Ex Maine Doug Member Posts: 162
    OK, separate circuit it is

    with one stat to run AC and steam boiler.  Having one stat on the wall with the Heat-Off-Cool switch handling which unit to use is the most important part of what I was looking for. Keeping the boiler on its own breaker and transformer is fine and as was pointed out, required.

    Thanks for all this input.  And I learned something.
  • Ex Maine Doug
    Ex Maine Doug Member Posts: 162
    edited July 2010
    Box Tstat

    The tstat you have was purchased from a "big box " store?

    Yes, the Honeywell Heat/Cool digital. It spent the winter just running the steamer as we had no AC.  In my Maine bank I have the VisionPro's.  Although I took one to Baltimore for the row home I just sold.  I like those but if my son wants one he can buy it. For now the old man installed a "low cost" stat. My labor rate is way way below market to provide those fancy stats.   
  • Techman
    Techman Member Posts: 2,144

    I love their food but most other things are NOT American standard. If you were living w/ that stat you'd be replacing it in several years and the actual "accuracy" is kinda OFF by a little .Next time you install a stat buy it from a repuital[?] supplier . There is a difference!!!!
  • Ex Maine Doug
    Ex Maine Doug Member Posts: 162
    When I was living overseas

    the stats just had numbers, not actual or set temps.  So we turned it to what provided the comfort level we expected, not to arrive at some accurate real temperature.

     If the  box store cheapo Honeywell  stat dies early the kid can buy the more pricey one.

    My VisionPro stats however came from a reputable supplier.  Thanks for your recommendation.
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