thermostats

My house was built about 1961

and it has copper tube radiant heat in the ground floor slab. It had an old GE oil-fired boiler. The swing between the coldest the house got and the hottest, with the thermostat set at the desired temperature went from about 66 to about 75 degrees, which is excessive. It also short cycled the boiler, not because of the thermostat, but because the boiler was oversized for most of the time.



I now have a mod|con with outdoor reset. This has made a huge difference. The trouble with the old system was that by the time the thermostat was satisfied, the floor was filled with 140F water and it kept radiating into the house for four hours or more. Then by the time the house got cold enough to trip the thermostat, the floor was cold and it took hours to heat it up again.



What the mod|con does, is that the outdoor reset puts water just the needed temperature into the floor, so it runs a lot of the time. As it gets colder outside, the water temperature inside gets warmer. Since this is my first winter with this new boiler, I do not have the reset curves set exactly right, but I have them pretty close. So the swings are now about 1 degree too hot and one degree too cold, which is a great improvement; in fact, it is acceptable. I have a fancy thermostat with 4 temperatures a day, but a simple one would be just as good, since with that monster slab in storing energy for so long, setback is not a useful option. (Upstairs, with Slant/Fin emitters, is a different story, where I set in about 3F of setback.)