Started this last year. The idea was to figure out if the furnace ran much more with the temp in the house set to 20 deg C all the time as opposed to having it
turn down the temp during the day and at night.
Because it never really got cold last winter, I wasn't able to draw any reasonable conclusion. Maybe it ran a bit more....
Last year from Dec to Feb the furnace cycled 38 times a day, 5.5 minutes / cycle, 1.6 cycles / hour and ran 9 minutes / hour. The mean temp was 0.13 deg C.
How does one go about figuring this out? Here you go.
In the basement, when the furnace motor kicks on, it pulls up the relay below and makes up a contact that turns on the battery on the right.
The now powered battery has wires that runs upstairs to this awesome clock I made out of an old hard disk drive. Now I know how long the furnace runs for.
I can make a clock like that for you. It's a great Christmas present! Contact me for details!
Then on the thermostat, I wired in a counter so I know how many times the furnace comes on.
The rest is math and we know math is fun!