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multiple thermostats

The 1966 Minnesota rambler that we just moved into this past winter that had two seperate thermostats (old mercury type) in the hall. One for the attic installed Central Air system and for the main level heating zone. The Central air system only cools the main level - the same area that is controlled by the adjacent thermostat for the boiler. I would like to combine the original main level thermostadt for the boiler with that for the main level cooling. Can I do this? Is there any specific type of thermostat that I should buy, or specific requirements? I currently have a Lux TX1500B which I did use in the winter, and it seems to work fine. It also works fine for the cnetral air. I've not had both systems connected to it at the same time for fear that since there were two seperate thermostats in the first place there must be some reason for that. Any tips or advice would be appreciated. Brian


  • Glenn Sossin_2
    Glenn Sossin_2 Member Posts: 592
    Central Air Stat vs heating stat for boiler

    It is not uncommon to see two separate thermostats - one for AC and one for heat. The AC guys want the stat located near the return grill so they can sense the temperature of the air coming back from all the different supply ducts. The thinking is, when it comes back too warm, its time to turn on the AC. Usually, the return duct is located in the middle of the house in a hallway.

    The heating guys don't want to measure the temperature in the hall, its usually not cold there, people usually not standing around there. There is no real heat loss occurring in the hallway. Most of the time, there are minimal cold surfaces like exterior walls and windows where heat loss occurs, so this is not a good place to sample air temp for heating decisions. They want the thermostat to be located in a room around chest height, where there will be heat loss occurring. They want the room where you are to be maintained at comfortable level - they don't really care about the temperature of the hallway - and shouldn't.

    You could use a combination thermostat, such as the LUX, but more often than not, the heating guy or the AC guy is not going to be happy about the location for the above reasons.

    Personally, I like using the Tekmar stats, they can be used with extra remote sensors that can be used to average temperatures in multiple locations. Let's say you put one thermostat in the family room and a 2nd remote sensor in another commonly occupied room of the house. Now you would get readings from 2 rooms and average them together to make the decision about heating/cooling operation from one thermotstat. Most versions of the Tekmar stats will let you add more than one remote sensor. The remote sensor doesn't even have to be visible - it can be set into the drywall and spackeled over - see attachment.

    The Tekmar thermostats are also smart. "The thermostat learns the recovery rate over multiple setback events in order to determine the proper lead time for the zone. The early start function, when used with cooling, allows the cooling system to turn on 30 minutes prior to the beginning of a period that requires cooling. The Early Start feature occurs when the schedule changes from a low temperature to a higher temperature."

    Hopefully this gave you a potential option.

    Good luck.
  • carol_3
    carol_3 Member Posts: 397

    You can combine your heating and cooling onto any thermostat provided that the thermostat has all of these terminals--two R terminals (one might be labeled RC), W, Y, and G. One of the Rs connects to the heating transformer, and the W connects to the heating equipment. The other R (maybe RC)connects to the AC transformer. The Y connects to the AC compressor, and the G to the AC fan. Your biggest challenge may be getting all the wires to one stat.
  • Brian_60
    Brian_60 Member Posts: 7
    Thanks for the reply

    It will not be a problem getting all the wires there as the two thermostats were right next to each other.
    The terminals are labeled G, Y, W, RH, B, O & RC
    There is a black jumper wire connecting the RH to the RC. I'm guessing that to connect the heating system and cooling system to the thermostat at the same time, I should remove the jumper. What do you think?
  • Paul Fredricks_3
    Paul Fredricks_3 Member Posts: 1,557

    Not seeing how things look, I'd venture a guess. Rh & W go to the heating system (yes, remove the jumper). Rc, Y and G go to the A/C unit. I'll assume you don't need to connect anything to O or B, but then again I don't know how things are set up.

    If the heat tstat has 2 wires connected and the cooling stat has 3, the above is probably correct.
  • carol_3
    carol_3 Member Posts: 397

    You got it right. Ignore O&B
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