The Wall
Forum / THE MAIN WALL / Two Stage Thermostats
  • Post a Reply to this Thread

    Two Stage Thermostats (9 Posts)

  • Greg Greg @ 4:24 PM
    Contact this user

    Two Stage Thermostat

    On a conventional Heat pump thermostat,say a T8411R,when does the second stage kick in? After a 3 or 4 degree drop in temp?I've read all the manuals and can't find the sequence of operation for the auxillary heat stage.I'm installing a hot water unit heater to back-up an existing in-floor radiant job, and i want to let the radiant handle the job when it can.Then bring on the unit heater when it's colder than normal outside (like it is right now!)Will this thermostat work for this or is there something better? Of course, this is a low budget job.The customer does'nt want to get to fancy
  • Kevin Kevin @ 11:36 PM
    Contact this user

    t8411

    I beleive its a 2 degree differential but i could be wrong. i know that a mercury stat would be a 2 degree differantial. If you go with a t8411, set the cycle rate to 1. Its in the instructions on how to.
  • andy andy @ 9:21 AM
    Contact this user

    I'm a little confuse,Why are you using a heat pump t-stat on a hydronic system?And as far as I know,the 2nd stage of heat kicks in when the t-stat is set at 2 degrees above room temp.or when the heater runs for more than a set time on single stage and can't satisfy.
  • Barry Barry @ 11:03 AM
    Contact this user

    No set temperature differential

    The T8411R, two-stage heat pump thermostat does not operate on a fixed temperature diferential between the first and second heating stage. The thermostat will automatically adjust itself so that the first heating stage will cylcle on and off an average of 3 times per hour. You can adjust the second stage to cycle on and off anywhere from three to, I believe, nine times per hour. Setting a higher second stage cycling rate will reduce the temperature difference between the cut-ins of first and second stage heating. Similarly, reducing the cylce rate will increase the temperature differential between stage one and stage two cut-in temperatures. As mentioned by others, I too am wondering exactly why you are attempting to use a heat pump thermostat on this system. Decent quality, digital, programmable thermostats are not super expensive. Heat pump thermostats are also equipped with "Emergency Heat" switches that are intended to energize resistive-type electric strip heaters in the event that the reverse-cyle refrigeration system fails to operate. For your application, this would not be applicable. I think you would be doing the customer a service by installing a non heat pump stat on the system.
  • scrook scrook @ 1:26 PM
    Contact this user

    I think he...

    meant he wants to use a 2 stage heat pump type t-stat to control two differant output devices radiant 1st then unit heater 2nd on a hydronic system. With some electronic 2 stage t-stats I suppose it is possible you could program the differential, but I never looked.
  • Greg Greg @ 6:58 PM
    Contact this user

    yes

    Scrook is correct.That's what i want to do ,but i can't seam to find any 2-stage heating only stats.They all have cooling too.I just wasn't going to use the emergency or the cooling features.I guess i should'nt have said "Heat Pump" .I meant 2 stage heating only. If you have any part #'s you can throw at me i would appreciate it. Thanks,and sorry for the delayed response.
  • Bob Bona Bob Bona @ 7:57 PM
    Contact this user
  • RichW RichW @ 8:53 PM
    Contact this user

    'stat

    Look at a White-Rodgers 1F95-371. I have one in my house. It's heat and cool- but it does what you want and more.
  • Greg Greg @ 9:15 PM
    Contact this user

    Thanks everyone(nm)

  •  
Post a Reply to this Thread