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Cost to heat different temps?

Dan_G
Dan_G Member Posts: 32
If my mod/con boiler (Munchkin 80M) with outdoor reset is set up properly to provide enough heating BTU's via the baseboard emitters to compensate for the structure's heat loss, then does it actually use any more gas/electricity to maintain an indoor temp of 66F vs 68F or even 72F?



I'm wondering whether or not the rate of boiler operation actually changes much to satisfy the t-stat?



I usually set the t-stat to 66F for the 10-12 hours I'm at work, and then up to 68-70F for 3-4 hours, then back to 66F at night for sleeping.



I'm wondering whether or not it makes more sense financially AND comfort-wise to leave the t-stat at 68F or 72F 24/7, and just adjust our clothing and bed sheets to compensate (wear/use less), so the structure as a whole stays warmer and doesn't have to recover from a temp drop.



Any insight is appreciated as I'm trying to better understand how this all works and stay comfortable through the winter :)
- Dan G.

Munchkin 80M

TACO 009, 007 circulators

SlantFin HWBB

Honeywell t-stats

Comments

  • Zman
    Zman Member Posts: 7,009
    Setbacks/ODR

    A condensing boiler will run most efficiently at lower water temps. You will also have less heatloss through piping and venting at lower temps.



    The  goal of you your ODR is to run the boiler at the lowest temp possible. This can be accomplished looking at the output of your baseboards at different water temps and matching that to the heat loss of the home at the same outdoor temps.



    As soon as you put a temperature setback in the equation, you have to raise the boiler water temp so that the boiler is putting out enough energy to increase the temp in the home rather than just  maintaining. This reduces the efficiency of the boiler.



    Short term setbacks will not save energy and should only be used if comfort is the goal.

    Set it and forget it.



    Carl
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Jamie Hall
    Jamie Hall Member Posts: 17,165
    The heat loss

    from a building, assuming constant indoor and outdoor temperatures, is directly proportional (or very closely so) to the difference in temperature between the inside and outside.



    Therefore, if you raise the interior temperature with the same exterior temperature, the building will lose more heat and the boiler will have to run harder or longer or both to make up for it.  There's no free lunch.



    Now setbacks throw a nice set of variables into that equation, and make it -- to say the least -- messy.  If you were to search the Wall here for comments on setbacks, you would find a lot of variations in opinion.  Bottom line is that the savings are not sufficiently dramatic to come up with a solid "do it".  On the other hand, it does not appear that they use enough extra fuel to say "don't do it".  Whether you save fuel over what you would have used at a constant temperature equal to the weighted average of the upper and lower temperatures (e.g. if you run 12 hours at 64 and 12 hours at 70, the average would be 67) appears unlikely at best.  So it becomes a matter of comfort.



    But, if you turn the thermostat down you are going to save energy.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • icesailor
    icesailor Member Posts: 7,265
    Set Back (again)

    Everyone says that there is no savings. They must be right and knowing what they speak of.



    My experience with set back thermostats is that for all the years and the four homes I had them in, no one can show me convincingly that I didn't save money.

    In my last Massachusetts home, I used 6 zones with 10 degree set backs. Two zones I will use as an example. Because that is the one I used the most. The period in the evening that was set UP was 68 degrees. The set back was 58 degrees. The set back occurred at 8:00 AM. One Sunday, I was sitting in the zone reading. It was 68 +/- at 8:00 AM. The outside temperature was 15 degrees. The circulator or burner never came back on until 4:00 PM when the thermostat called for heat. The inside temperature was 61 degrees. So, the temperature dropped 7 degrees in 8 hours. We'll call it a degree per hour. I have a FHW oil boiler set at 165 degrees high limit but it was designed for 180 degrees and had mostly that amount of installed baseboard. It is fired at .85 GPH. It took the circulator/burner 50 minutes back to 68 degrees.

    I started to use set back thermostats in 1971. I know how much fuel I burned in a given period. After I put in the thermostats, my fuel use in gallons went down.

    The biggest advantage of set back thermostats is never discussed. That is that people will find out how comfortable they cab be in a room where the temperature is controlled. You would be surprised how comfortable you can be in a sleeping room where the temperature drops into the mid to low 50's. But how comfortable it becomes when the heat rises 8 degrees as you get up and the bathroom and the rest of the house is warm.

    ODR equipment would really be the nuts if they could over ride the outside temperature when you raise the thermostat. That's the missing link in ODR.

    Lowering the inside set temperature is the same as raising the outside temperature. Raising the inside temperature is the same as lowering the outside temperature. The ODR control is clueless that it is happening.

    If you try to use them with ODR and maintain the minimum temperature, it will take forever to recover. If ever.