Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

HVAC Designer

Why would the attached gas/DX rooftop

unit thermostat have (4) mercury switches in it.  I think you only need 1

for heating and 1 for cooling.  Please explain this Honeywell standalone

thermostat to me.

I know what the heat anticipator does,

but there seems to be (2) heat anticipators in this thermostat (one set for 0.6

amps and one set for 0.375 amps).Does it have to do with defining the deadband (on - off) or does it have to do with 2 stages of heating and 2 stages of cooling?


  • Empire_2
    Empire_2 Member Posts: 2,343

    I have to say, seeing the mercury bulbs is rare now-a-days' and being 2 stage is just plain unusual.  Your dead band is the diff. between the heat and cool, so dead band is fixed at what ever you set it at.  Your anticipation is set at .6 for first stage and the 2 stage is definitely lower, but how did you come to the conclusion of, .375?  Any way's... Your RTU is 2 heat/ 2 cool and depending on the actual equipment, the t-stat can handle stg 1 &2 cooling and stg 1 &2 heat. 

    2 stg cool is either mechanical cool plus economizer/or 2 mechanical cool + econo.  Heat is either 2 stage gas valve, or 2 actual gas valves.  As far as the anticipators are concerned, stg #1 is set using your induce draft motor, any timing circuit (stg1 anticipation includes all operating controls) and is the start of your heating cycle.  Stg 2 is usually only the gas valve solenoid alone.  That's why it is set at a lower amp draw.  The reason it's lower is that stg 2, being only the solenoid, will drop out first then stg 1 to finish the heat cycle.  Your dead band and differential have nothing to do with each other.  Dead band typically is set at 2*, but by no means is it law.  Heat differential is there just to assure that when stg #1 shuts down, the temp will closely match actual room temp.

    Mike T.
  • Designer1
    Designer1 Member Posts: 6
    bedroom radiator air vent gets water-logged

    Mike T.,

    Thanks for the excellent reply.  I printed it for future reference.

    Since you know HVAC very well, I have another question.

    I have a 1-pipe steam system in my home with a newer boiler.  There is a 1-1/4" takeoff in the basement up to the second floor bedroom and bathroom.  The 1-1/4" line splits into (2) 1" lines.  The bathroom radiator is a small wall-hung unit that heats up very easily.  The bedroom radiator is slow to heat.  I replaced the air vents with adjustable air vents.  The bathroom one is set at 1 and the bedroom one has the adjustment knob completely off for maximum venting.  The bedroom radiator works for about 1-2 days and then I have to take it off and water pours out of it (it gets water logged with condensate).  The radiator is slightly pitched because I checked it with a level.  Do I need more pitch?  Why is the air vent not draining.  It is a high-end DOLE radiator air vent.  Also, the radiator makes a slight popping sound.  If I need to, I will gently increase the pitch with 2x4's (one as a fulcrum and one as a lever).  What do you suggest?


    found that the bedroom and bathroom share a common 1-1/4” riser and must split

    under the 2nd floor flooring.  1” goes to my bedroom and 1”

    goes to the bathroom.  The bathroom always heated up fast.   I

    adjusted the air vents by opening the bedroom one and closing the bathroom

    one.  We now have heat in the bedroom but it is not reliable unless I take the vent off and drain it daily.
  • JStar
    JStar Member Posts: 2,752

    Were both radiators always on the one line? Was one added? What pressure is your boiler set for?
  • Designer1
    Designer1 Member Posts: 6
    bedroom steam radiator air vent water logged

    One radiator was added at some point since the house was built in 1930.  I know this because all of the other bedrooms have 1-1/4" steam supplies, but my bedroom has only 1" and the bathroom has 1".  I also know that there is only one 1-1/4" feed from the basement.  This is the only branch from the main that has a split in it.  My guess is that bathroom renovations on 1st and 2nd floors over the years caused the system to be modified.
  • Designer1
    Designer1 Member Posts: 6
    boiler pressure

    the boiler pressure is set very low (about 0.5 psi).  I read The Lost Art Of Steam Heating and fixed that myself with a screw adjustment at the boiler.  I also use SQUICK every heating season and change the thermocouple when needed.  I also drain water out of the condensate main and boiler at least twice a winter.
  • JStar
    JStar Member Posts: 2,752

    Can you take pictures or measurements of the two radiators on the one line? There may be too much condensate for one supply line to handle.
  • Designer1
    Designer1 Member Posts: 6
    bedroom radiator air vent water logged

    Why would my bedroom radiator air vent be water logged? 

    It seems like the steam going to the bathroom radiator is preventing the bedroom radiator from draining properly.  I did hear sounds last night like pop-corn popping.

    A plumber suggested that I completely shutoff steam to the bathroom radiator to test this.  However, I am afraid of the leather seat coming lose and clogging the supply line.

    The bathroom radiator is wall hung, so it has a good amount of height to help it drain.

    Would pitching the bedroom radiator help at all if the steam to the bathroom radiator is blocking the condensate?
This discussion has been closed.