Originally Posted by dipstick
So as long as it is above freezing turning the heat off will save you money.
There is a minimum energy cost setting for your thermostat involving nighttime setback, and daytime setback while you're gone.
Exact analysis for this is not worth it for residential use but with experimentation you can come close.
This is a science problem.
There is also a discomfort factor in coming home to a cold house and waiting for it to warm up.
This is a psychology problem.
This factor can probably be converted into dollars by asking yourself: "How much would you pay each day to come home to warm house?"
Ask each family member because each has a different 'utility function' for money and for comfort.
This converts the psychology problem into one of economics.
There is also radiative heat loss which means a 72F air temp may feel cold depending on the temp of the walls, which depends on inside and outside factors. High end thermostats sense outside temps and correct the inside temps.