Have received so many really good answers to problems and questions I've
posted in the past, thought I would post something positive, for once. So,
I'll share my experience on this subject with everyone.
Live in Mass. in a typical 30 year old colonial with gas, forced hot water
heating on two zones.
Have always had the Honeywell mechanical thermostats for each zone. The
ones with the bi-metallic coiled spring with the Mercury switch vial on the
For 30 years, my wife was always complaining about the large temp swings
that would occur in most of the rooms.
I tried playing with the heat anticipator, but nothing really changed.
Well, this year I finally broke down and put in two Honeywell digital
All I can say is Wow.
(no, I don't work for Honeywell)
No matter when you look at them, the set point is exactly the same as the
resultant room temp.
No more wide fluctuations.
Probably due to a very tight hysterersis loop characteristic on the new
(resulting in much tighter control)
Don't like the idea that it requires a battery, but heck, I can probably
remember to change it once a year.
A good question is whether I will be paying more for heat now.
The old furnace mode was, of course, wide temp swings with the furnace going
on and off rarely, but staying on longer.
Now, with very frequent on-offs, but shorter actual furnace runs each time.
Have no idea how this relates to actual heating costs, or efficiency ?
Anyway, for anyone still using the old Mercury ones, my suggestion is to
really consider getting one of these new digital ones.