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Thermostat-Boiler Conversations

swellmanswellman Member Posts: 14
I have what I hope is a possible thermostat setup (see attached image). Can anyone tell me if they think this could be setup (note I have an old Raypak boiler (25-30 years?) with a single common wire). I’m wanting the circulator to always be on in the basement zone but only want the boiler on when the basement is calling for heat. But then I also want the upstairs to be able to call for heat but it needs to turn on it’s circulator AND the boiler... again, possible? You tell me :)

Comments

  • Jamie HallJamie Hall Member Posts: 12,954
    Lots of different ways to wire that up. It depends, first, on whether the circs are 120 volt (likely) or 24 volt.

    If it were mine, I'd wire it so that circulator 1 was always connected to power -- thought a switch and fuse, of course. Assuming thermostat 1 is 24 volt (and doesn't need a common), it goes direct to the boiler controls. Thermostat 2 then goes to the circulator -- through a relay if the circ. is 120 volt -- and the end contacts go to the boiler controls in parallel with thermostat 1. You will need a power source for the relay and thermostat 2.
    Br. Jamie, osb

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
    swellman
  • HVACNUTHVACNUT Member Posts: 3,415
    We need to see the boiler wiring diagram and the zone control(s). It can be done. Other than constant circulation on the basement zone, its typical. Why do you want constant circulation in the basement? When upstairs comes on, the basement will heat as well. 
    STEVEusaPAswellman
  • swellmanswellman Member Posts: 14
    @HVACNUT - We are working on doing a two zone system using two circulators (no zone valves). We have three loops on the basement zone (with one of those loops having two rads in the basement and two in the back rooms which form an addition on the main floor of the house). The second zone is the (original) main floor and second floor. Most of the rads in the basement are new fancy aluminum looking ones. The rads upstairs are all cast iron.

    I'm imagining:
    - Basement is heated to a value equal to or greater than the set temperature of the basement thermostat
    - Main floor is heated to a value equal to or greater than the set temperature of the main floor thermostat
    - Boiler doesn't need to be called for heat because there is sufficient heat everywhere
    - BUT basement will lose heat fastest because of the aluminum rads
    - AND our upstairs rads always seem to feel a bit too hot when the basement is being sufficiently heated (though I note this reality is currently all a single circulator system)
    - I assume that if I have only circulators for zoning and no zone valves, there is still *some* circulation to the upstairs zone even when it is just the basement circulator running <-- is that true??
    - Because the upstairs rads are cast iron and the basement is losing heat faster, *some* small portion of the heat residing in all that cast iron upstairs could be "reclaimed" by the downstairs rads if the basement circulator is left to run.
    - I don't want to leave the upstairs circulator on running full time because I know that my upstairs is already too hot compared to the basement but in the case of the basement it seems like it could be running when the boiler is on (like it needs to be) or when it's off (at worst makes no difference but as I've maybe(?) speculated it could make a small difference on how long it takes the basement to drop back down below the set temp of the thermostat).

    It was a fun thought experiment anyway if it turns out to be wrong (or crazy...or both) :)
  • Jamie HallJamie Hall Member Posts: 12,954
    First off -- there should be no circulation in a zone for which the circulator pump is not running -- that addresses your concern about the heat seeming to get to the upstairs zone. Likewise, there would be no circulation from the upstairs radiators to the basement zone...

    If the system is piped correctly. This is strictly a piping problem. This is not to say that there aren't a lot of systems where you do get "ghost flow" in a zone which is not calling for heat! But it shouldn't happen.

    That said, if the system is piped correctly, the two thermostats -- and associated circulators -- should have no problem controlling the temperature in the two zones quite independently. Which, incidentally, you will need to do, as the response characteristics of big cast iron radiators are quite different from those of other types of radiators. But that becomes more a matter of getting the thermostats properly set up.
    Br. Jamie, osb

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • mattmia2mattmia2 Member Posts: 1,443
    You're overthinking this. Pipe it primary-secondary, put a mixing valve with outdoor reset on the cast iron zone so you can keep the supply water temp matching the load, and do it one secondary pump per zone.

    If the radiators aren't too oversized, you should be able to do it with just the heat anticipator on the t-stat for the cast iron zone, but you will have to be careful to keep the boiler temps high enough to keep it from condensing. It is ok for it to condense briefly at the beginning of a cycyle, but it will destroy the boiler if the temps are low enough to cause sustained condensing.
  • swellmanswellman Member Posts: 14
    That helps a lot. I guess because it was originally a gravity system I wondered about flow naturally occurring in the upstairs zone even with just the other pump on. I guess I can’t say I know for sure how the way it’s piped will or won’t play into it but it does simplify the thermostat wiring that I could default to the more simple wiring solution where both thermostats can just talk to their respective circulator and subsequently talk to the boiler. Thanks again.
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