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Newbie; basic thermostat questions - help w/direction?


Hi all, a friend recommended the forum for boiler stuff. My 1928 duplex in Michigan has a weird setup. Steam for the upstairs, and hot water for the downstairs. The downstairs has two pumps, and two zones. I'll provide photos later of the model numbers. I want to ask if someone can help provide direction on selecting new thermostats. I promised the new downstairs tenant that I would replace one of the thermostats because it is an ancient one with a clock in it (like a Honeywell T852AY) and it's making an annoying grinding noise. I started googling "picking thermostat for hot water boiler" and was surprised at the lack of info.

Three main questions:

  1. Generally; are there special rules about selecting thermostats for old boilers?
  2. This specific zone is in a crawl space, which regularly goes below freezing. The current thermostat does not allow you to go below 55 degF and also doesn't allow you to turn it "OFF". Are there new thermostats I can also require a minimum temperature?
  3. The lower unit also has forced AC, which has it's own thermostat. The wiring is on same wall, so I would much prefer to combined the AC and heat into one stat on that wall if possible.

Thank you!



  • HomerJSmith
    HomerJSmith Member Posts: 2,468
    edited May 11

    The oil schedule has to do with the original pumps (B&G series 100). The replacement pumps are those 2 round greeny thingys bolted onto the pipes. They don't need any oil because the bearings are lubricated by the water running thru them.

    Your installation is wrong. That big red round thingy is in the wrong place as is the the brown rusty thingy that it is screwed into. They are both on the cooler water return to the boiler. They should both be on the hot water supply before the pumps which is the highest temp so that the air entrained in the boiler water can be eliminated from the sys. The pumps can stay where they are, on the hot water supply.

    To address your original question, Ya, you can use just about any thermostat you want except a thermostat that requires three wires ( a charging thermostat. think NEST). Any two wire thermostat, battery operated display or not.


  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,099
    edited May 13

    Any thermostat that can operate both a heater and an air conditioner will have an OFF position, so to protect the crawl space pipes from freezing, you will need to add another control to operate the boiler even if the thermostat is OFF, if the crawl space temperature gets below maybe 40°F or 45°F. A tenant may do that to you to save on their operating cost (if they pay for their own fuel) when they go on vacation in January. Why pay for heat I can't use while I'm in the Bahamas for a week.

    Here is a thermostat that I would suggest for your situation TH1110E1000

    www.supplyhouse.com/Honeywell-Home-TH1110E1000-E1-Pro-Non-Programmable-Thermostat-1H-1C this is low cost and will do the job for you.

    The additional control to protect the pipes from freezing might be this one mounted in the crawl space.

    https://www.supplyhouse.com/Honeywell-Home-T410A1013-T410-White-Electric-Heat-Thermostat You must be careful where you locate the freeze protection thermostat so that when the craw space reaches 40° or 45° it does not cause the room temperature to exceed say 60°, or you may get complaints of overheating.

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • Big Ed_4
    Big Ed_4 Member Posts: 2,806

    WWII "the big one" ;) generation boiler tags .. Typewriter and good penmanship …..

    There was an error rendering this rich post.

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,099

    Here is the diagram for the wires using one thermostat for both the heat and the cool. The cooling system has a separate transformer, and the heating control has a separate thermostat, so you will need to remove the factory installed jumper that connects R and Rc on the thermostat.

    Once that is complete you connect R, Y, G, and C from the Air handler of the cooling system to To Rc, Y, G, and C on the thermostat Follow the color code from the Air handler R to the RC on the thermostat. G to G, Y to Y, and C to C.

    Then the R on the thermostat and the W on the thermostat are for the heating system. Connect R from the thermostat to one of the T terminals on the R832A and the W on the thermostat to the other T on the R832A

    Finally select an appropriate location for the T410 in the crawl space and connect the L1 on the T410 to the T on the R832A and the T1 on the T410 to the other T on the R832A.

    I used a Red wire with White stripes to illustrate the difference in the R and the Rc. Electric is colorblind, so use the red wire in the air conditioning thermostat for Rc. Just be sure that you do not mix them up or you may be buying a new transformer or new circulator relay.

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • WillGreenlee
    WillGreenlee Member Posts: 2

    Thank you for the diagram! This is quite helpful. I will study it and also take a look at the existing AC wiring to see what it looks like and go from there.