Ignoramus10802 wrote:
i
It's far more complicated than that. Factors such as insulation / heat
loss, type of heating, multi-stage heating, electric backup heat on heat
pumps, etc. all come into play in determining the away duration and temp
reduction where savings begin, and in some cases (typically high
efficiency homes) it can require a multi day absence to see any savings.

This is patently untrue.
No, there is quite an element of truth! You have to compare the thermal
mass of the house and the heat loss. If the house had enormous thermal
mass, like lots of stone floors and massive stone fireplaces (some
people build houses intentionally to have very high thermal mass) then
although the furnace could warm the air quickly to make you comfortable,
it would still run for hours to warm up all that mass. If you have a
lot of thermal mass and low heat loss (good insulation) then turning the
thermostat down for a couple hors gives no benefit. If you have low
thermal mass and lots of heat loss, then turning it down for even a
couple hours will give significant benefit.

Jon