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wire two thermostats in parallel?

AJW Member Posts: 5
I have a single-pipe steam system that works relatively well (one or two minor complaints, but I'm working on that...).

The problem is that the 2nd floor is typically colder than the first. Knowing heat rises, I find this strange (it's a fairly open floor-plan; 65yr old center-hall colonial).

Regardless, I have a thermostat in the back hallway on the 1st floor for the boiler. There is a great Honeywell thermostat on the 2nd floor just for the central air (was installed in the attic).

Since the temp varies by minimum 1deg, and I've seen it has high as 3deg, my question is whether I can wire the two thermostats in parallel to the boiler?

I know how to make the connections, but I'm asking whether this will work?

If both "call for heat" at around the same time, that should work fine. But what if one calls for heat and then shuts off, and the other therm. calls for it just after? Would the boiler fire-up again, even though it just cycled? Or will the boiler's circuts figure this out and let its "cycle complete" before allowing it to fire again?

Any assistance is much appreciated!


  • Mark Eatherton1
    Mark Eatherton1 Member Posts: 2,542
    Who told you heat rises...

    Next time you see them, you grab their tongue, pull it out and give it a spanking for lying to you...;-)

    Hot air rises, hot fluids rise, and some times here on the wall, tempers rise.., but Heat, in its true thermal energy form, flows from Hot to Cold, always and forever, thru the path of least resistance. In other words, in ALL directions, depending on the differential.

    This is mother nature at her finest. You see, she despises imbalances. Imbalances in ANY thing, be it pressure, temperature, humidity, EVERYTHING. Now in her unending effort to balance things out, she wants them to equal each other, hence the flow of energy from hot to cold.

    But I digress...You were asking about wiring thermostats in parallel, which I have seen numerous times and can tell you that in your case it's probably not a good idea. Most places will over heat, then the single pane, double hung, wood framed thermostats (windows) kick into action (not a good thing) and the meter starts ta spinnin'.

    The best and smartest thing you could do would to be to install individual non electric thermostatic control valves on all but ONE radiator. Then, choosing that ONE radiator in a worse case heat loss scenario (typically top floor, outside corner, facing NE or NW) install one programmable thermostat in that location.

    You now have an efficient steam heating plant. Provided that all the other cast of support characters are in line, the system should work fine and the residents will be more comfortable then ever.

    You might be able to enhance it's operation a little better by adding a tekmar two sixty eight?? steam boiler control. Also make sure your system has good accurate controls (safety and otherwise).

    Just kidding about the tongue spanking (YUCK!!)...

    Happy Hydronicng Holidays!

    By the way, let me guess on the complaints, one says they're too hot, and the other says they're too cold...

    How'd I do??


  • Mad Dog
    Mad Dog Member Posts: 2,595
    Mark covered it all.........................

    I too, always wanted to do that, and when I did - with steam - we had mixed results. Mad Dog

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  • Jason
    Jason Member Posts: 17
    it can be done

    i'm no pro... just a homeowner that frequents this site. i'm not making any claim that your transformer can support 2 stat anticipator loads or any of that. but i can tell you that my 3 family house had 2 parallel T87 stats on a one pipe steam system when i bought it and the system functioned. but it doesn't make a very good control system. the result is almost always overheating in the area that isn't calling for heat. i balanced my house with radiator venting and disconnected one stat.

    get the lost art of steam heating and read the part about venting or go to gorton's website and look at their recommendations for how to balance a system with only one stat. the right venting will help steam get to all your radiators at the same time rather than the 2nd floor lagging your first floor.

    i tried just about everything along the way while i was learning about steam and probably spent twice what i needed to if i had known how to do it right from the beginning. i have one whole floor (3rd) set up with the trv's that mark mentioned and they do work great and allow you to adjust the temp in any room. but they cost quite a bit for each radiator and you still need properly selected high quality vents to balance the house. so now i wish i would have saved the money i spent on the trv's (and various junky/wrong vents, etc.) and just bought the right gorton vents the first time. the trv's are nice if you can afford it. in a house with 20 radiators, i couldn't. but with the right vents in the right places, you can make it pretty comfortable.

    and to answer the original question about cycling, whenever either one of those mechanical stats calls for heat, the burner will fire (unless something else is locking it out). if you have a weird thermal response in your house such that one stat would become satsified around the time another would begin to call for heat, then yes the burner will fire. seems unlikely though. usually various room temps are moving in the same direction up or down. my house's situation was that if all stats were set and left alone, then the same one would always call first and when it was satisfied, the other one would have already been satsified too. so effectively one stat was always in control anyway depending on which had the higher relative set point but there was always a temp differential. but this depends alot on your house's specific thermal response characteristics.....

    again i'm just a homeowner that reads this site so keep that in mind. mark and mad dog and most of the other regular posters here are pros.
  • Nice, Jason

    Well put.

  • David Efflandt
    David Efflandt Member Posts: 152
    body heat and solar gain

    I balanced my air venting to best keep everything the same temperature (which takes some experimentation when rads are not optimally sized). But there are still going to be differences based on what is occupied (body heat) and how solar gain is distributed.

    My upstairs has south facing windows, but lower level is shaded by unheated south porch. So during the day upstairs gets a little warmer, or a little cooler in the evening when downstairs is occupied. An electronic thermostat that bumps up a degree or two for awhile in the morning, makes it easier to crawl out of a warm bed.
  • Mad Dog
    Mad Dog Member Posts: 2,595
    But you have a great observation to offer

    we appreciate the input, pal. Mad dog

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