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Does thermostat setting really matter?

Lets say you keep your target temp at 68, would setting it to 72 really make a difference? My theory is that all the energy was expended to get the water to turn into steam already, and if it's already steam, keeping it there for a few more minutes won't matter.

Regardless of whether the house is at 68 or 72, you'd assume that the temperature would drop at a similar rate and cycle the boiler with the same frequency either way.

So, on steam heat, does a couple of degrees really make a difference? On forced air other instant heat types I think it would, but it seems like it shouldn't matter much with a boiler.



  • Jamie Hall
    Jamie Hall Member Posts: 23,286
    Say what? The heat lost by the structure is directly related to the temperature difference between inside an outside. Therefore, it will be greater at 72 than 68 -- for instance.

    That heat loss must be made up by the heat source, and what that heat source is is quite irrelevant. As is often said, a BTU is a BTU.

    The problem with your theory is simple: the heat produced by the condensing steam is produced very rapidly indeed -- and if the steam isn't constantly replaced, the radiation will cool off and no longer deliver heat. Therefore to deliver a certain number of BTUs to the space -- to keep it's temperature constant -- a certain number of BTUs of steam must be condensed, and that steam must be replaced by the boiler. At a greater heat loss rate, the radiation must run either longer at a time, or more often.

    So... if you keep the house warmer, the boiler will either cycle more often, or for a longer time.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • bburd
    bburd Member Posts: 912
    As a general rule of thumb, fuel consumption will decrease about 3% for each degree of reduction in space temp set point for heating, regardless of heat source. This is for systems that maintain a constant temperature. 

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,835
    Basic rule in heat loss calculation starts with the U value of the structure. The U value is the rate BTUs/h travel thru a 1 square foot area when the temperature difference from one side of the area is 1° different than the other side

    So the total load calculation is based on the total of all the U values of all the square feet of the structure added up to a total. That total is then multiplied by the temperature difference between one side of the structure to the other side. If You make that temperate difference 4 degrees more then the load calculation will be greater by about 12% at the temperature range you proposed in your query.

    If however, you are going to compare your beliefs with the facts, no one here will be able to convince you that your theory is flawed. With that said, set your thermostat at 72° and be more comfortable. If however, you find that you are using more fuel than in previous winters when you set the thermostat at 68° setting, then you might want to rethink your beliefs and look at the facts more closely.

    One more thought... If your theory were to hold true, then why stop at 4°F? Why not set the thermostat to 90°F and wear swimsuits around the house all winter. You could also grow tropical plants and have no need for expensive winter clothing, Think of the savings!
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics