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Outside temp dramatically impacts thermostat settings

When the outside temperature is in the 40s we set the thermostat to 66 or 67 degrees and all floors of the house are fairly evenly warmed (upper two floors a bit warmer).  But when the temperature outside is below freezing, particularly in single digits, we have to set the thermostat to 60 degrees to keep it from getting to hot.  And the upper floors become much warmer than the first floor.  We have a steam boiler and three floors.  What could be causing this dramatic change in thermostat requirements from the outside temperature change?


  • Jamie Hall
    Jamie Hall Member Posts: 22,893
    Poor balancing

    plus a chimney effect.

    But the main problem usually is poor balancing and, quite possibly, inadequate main venting.  Is this a one pipe or two pipe system?  The approach to balancing is different.in the two cases.

    What is happening is that on the longer runs the upper floor radiators finally get really warm.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Bullethead
    Bullethead Member Posts: 21
    It is a one-pipe system

    It is a one-pipe system with Groton Air Eliminator vents at both ends of the main in the basement.  The radiators heat up about the same time.  Upstairs heats up only a short time after the downstairs. It is now 50 degrees outside and I have to put the thermostat to 69 degrees to get the same temperature in the house as 60 degrees on the thermostat was getting me when it was 15 degrees outside.  And now the house is pretty evenly balanced but was much hotter upstairs than down when it was 15 degrees outside.
  • Mike Kusiak_2
    Mike Kusiak_2 Member Posts: 604
    Thermostat location?

    Where do you have the thermostat installed?

    Is it an area that accurately indicates the average temperature of the building, and not installed on an outside wall which would be unduly affected by outside temperature?
  • Bullethead
    Bullethead Member Posts: 21
    Thermostat Location...

    Thermostat is on outside wall in coldest part of house by front door.

    Seems there are two things I should do:

    1. Move thermostat to middle of first floor, which is the least insulated floor in the house.

    2.  Put TRVs on the four upstairs radiators.

    Seems likely it will balance the heat.
  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,576
    Temperature imbalance

    Is your thermostat properly setup for steam?--NBC
  • Bullethead
    Bullethead Member Posts: 21
    Thermostat set for steam?


    I don't know.  I did not even know there was such a thing.  What does it mean and how can I check?

  • Bullethead
    Bullethead Member Posts: 21
    How to balance one pipe system


    What is needed to balance a one-pipe system?

  • ChrisJ
    ChrisJ Member Posts: 15,439

    I like your thinking!

    The thermostat certainly shouldn't be on an outside wall insulated or not.  I would put it far from a heat source and certainly far from an outside wall or draft.

    After that I would look at balancing the radiators as necessary and if need be install TRVs in overheating rooms.  We balance radiators by venting them at different speeds.  

    How are your main vents and pipe insulation?  Do all radiators heat at approximately the same time?   All radiators should get steam to the pipe at the same exact time or as close as possible. 
    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment