If I remember, this question was about the "setback" when programming
a thermostat. The question was quickly, or originally confused with the
"differential setting" of a programmable thermostat.
No one has pointed out that some (at least one that I know about) have
a "differential setting" that can be programmed. That value is
nominally set to "10" on the stats I've programmed, and the value is,
I think, 10x the on/off degree difference for the system. This is
sometimes called an anticipator setting, I think.
The 10 "degree setting" that the original writer heard about on a
radio show (or somewhere) for the "differential" has NOTHING to do with
how low a thermostat should be setback.
Perhaps someone who has access to the original posting can check this
out, since I am not an expert in heating systems. Because of this,
I have been waiting for an expert to comment; since that does not seem
to be happening, I'll take a chance that my understanding of the
"differential" setting on a programmable thermostat is correct. --Phil

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Phil Munro Dept of Electrical & Computer Engin
Youngstown State University
Youngstown, Ohio 44555