BillC wrote:
HI,

I set the thermostat timer for a minimum overnight temperature of 45
degrees, to heat to 70 at 6:30 AM. Effectively, this leaves the
furnace turned off overnight. I figure that saves wear on the furnace
/ fan and saves fuel costs overnight.
However, I heard on a radio program that thermostat timers
should only have a max differential of about 8 or 10 degrees.

Anybody know what the best settings are?

For conventionally fueled systems (oil, natural gas) the longer you leave
the furnace off, the more you will save. All the "maximum setback" talk is
just noise, without any basis in scientific fact.

Courtesy: http://www.nol.org/home/NEO/sept2001/sept003.html

"Heating and Cooling Myths
A common misconception associated with thermostats is that a furnace works
harder than normal to warm the space back to a comfortable temperature after
the thermostat has been set back, resulting in little or no savings. This
misconception has been dispelled by years of research and numerous studies.
The fuel required to reheat a building to a comfortable temperature is
roughly equal to the fuel saved as the building drops to the lower
temperature. You save fuel between the time that the temperature stabilizes
at the lower level and the next time heat is needed. So, the longer your
house remains at the lower temperature, the more energy you save. "