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Swing or Differential Setting on Thermostat

Curious what others think is a preferred way to heat up a steam system. My thermostat came out of the box with a .5 swing setting. So if I set my temp to 70 degrees, the boiler will fire at 69.5.

Using this method my boiler ran about every 30-40 minutes with a runtime of approx 20 minutes. I then changed it to a 1 degree swing setting. So now at 70 degrees, it waits until 69 degrees to fire the boiler.

Now it runs every 60 minutes for about 30 minutes. The downside now is that the temp "undershoots", so yes it will fire at 69, but by the time the steam reaches the 3rd floor thermostat, it dipped to 68.5.

Thoughts on which option is better? I've read longer run times were better, that is why I changed from .5 to 1.0 differential on my thermostat. But I also wonder if the system being off for those 60 minutes cools off all the piping too much and is actually more wasteful and uncomfortable for the apartments.


  • Jamie Hall
    Jamie Hall Member Posts: 15,856
    It's much more a matter of comfort than it is of efficiency -- there will be some change in efficiency, but which way I'd not care to say -- and it will be small. If the 0.5 swing allows a long enough run time to get all the radiators warm, I'd probably set it that way.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
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