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What is the best night setting onthermostat?

In a study they did many years ago now, no more than 4* night setback heat or cool for the very reason described. If you set the temp back too much you will spend more money catching up in the morning than you saved overnight. I had a bank once with granite counters. They turned the heat off at night. The girls were always freezing. Why? Because even at 3 PM when the room temp said 70* the counters were only 56*. Once we stopped them from setting back so far and the building's mass caught up to air temp, everything was fine.


  • N. Ani
    N. Ani Member Posts: 1

    I work in a large school building. Some people say that we should put the night setting on the thermostat at 65 so that it will not take too long to heat the building in the morning. Some say that we should put the night setting at 50-55 in order not to waste heat at night. Which would be the most efficient and cost-effective way to do it?
  • adambuild
    adambuild Member Posts: 413

    I agree with the 4* max setback. We use only the Honeywell VISIONPro 8000 series and love them. For a school you might even want to use their remote sensors.
  • Rich Kontny_3
    Rich Kontny_3 Member Posts: 562

    *In the early eighties the government mandated up to 15* setbacks. Then it was determined that in order to heat back up solid objects (thermal mass it took almost as much energy! 4* sounds very reasonable! One could do a wider setback on weekends or holiday periods.

    Rich K.

    Happy Thanksgiving!
  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928

    I will state with absolute certainty that unless the boiler has fired at least once during the setback period there has been zero energy savings and nearly positive certainty that energy savings is slightly negative.

    The colder the weather, the deeper the possible setback but there's the crazy problem that the deeper the setback the longer it takes to recover the air temperature and longer still to recover the mean radiant temperature. That's why deeply setback systems will short cycle a number of times after they have achieved the air temp setting. The air itself has to heat the walls and objects in the space yet the walls/objects are cooling the air faster than it can warm them...

    Fairly deep setback can be used over a weekend but you must let the system begin to recover early enough to warm the walls and objects lest people complain about feeling "cold" and asking you to turn up the heat and shortly after it's turned up telling you it's too warm!

    Setback during a long (say a week or so) of no occupation is a no-brainer. Setback as far as possible to prevent the possibility of freezing, but the recovery period will likely take at least two days to get the mean radiant temperature up to normal.

    I know of one and only one reasonably effective setback strategy that works regardless of the weather and the length of the setback period. Calculate and provide the supply temperature required via outdoor reset to maintain the lower room air temp during the setback period. The boiler will only stop providing heat during the period it takes for the "normal" supply temperature to drop to the "reduced".

    Unfortunately this requires some VERY intelligent boiler control and is likely impossible with steam unless it's a Vari-Vac or original, solid-fueled vapor system with a highly sophisticated control system. If steam, look into the finest Heat Timer controls as they'll do their best to approximate as long as you set them properly.

  • Right...

    In the bank, the rooftop furnace WOULD short cycle all day because it would heat the air up and the cold mass in the area would cool it right back down when the furnace shut off. I was baffled until I took a surface temp reading of the granite and found it to be 56*, then it all became very clear. A perfect example of the "Cold 70" someone around here talks about. He knows who he is... ;)

    Once we reduced the setback all the little electric heaters under the teller stations started disappearing. Think of it, you got your furnace going on and off all day trying to warm up the mass in the space PLUS all the girls each have their own little electric resistance heater at their feet. Nope, no energy waste going on there...
  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928

    You got it!

    I used to be baffled at how I could possibly be comfortable more comfortable before daybreak in my fully internal "reading room" at 63F or so with trousers at my ankles than in my true office at about the same temp. Radiant floor (of course) in the bath, but it's wildly connected to the system and in most weather is little more than neutral to the bare foot.

    Then I took temp measurements. In a 40 sq.ft. (gross) bath: The 12 sq.ft or so of 1 1/4" thick soapstone countertops were within 1 degree of the temp of the 15 or so sq.ft. of heated floor area and actually slightly warmer than the air. The nearly floor-to-ceiling wall tile and the throne itself were also slightly warmer than the air.

    Stark contrast to my highly exposed office (it's century-old house with huge windows and only modest but meticulously installed insulation/weatherization) where the outside walls--not to mention the windows--are below the room air temp.
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