Heathkit used to sell such a thermostat kit maybe 20 years ago. I
bought/built one. It had to learn how fast it took to get the temperature
up to the set point at the end of the setback period. However, after a few
years it would frequently malfunction such that the heat would stay on
continuously. I came home in the winter and the inside temperate was 80F.

--
Larry
"stu" wrote in message
...


Unless you have an adaptive
thermostat/control that estimates the exact time to reset back to 70F
such
that the temperature just reaches 70F at the end of the setback period.
Such a control might be fun to build and tinker with, but I don't think
a
retail unit is available.

daestrom
little late i know but thermoststs like this are made, honeywell i think
make them. if anyone is interested(and still reading this thread) i will
dig
up the info.