My apologies in advance, because I know we've already discussed this before, but for some reason I can't find any explanation through my various searches.

As I've discussed before, I've installed a ZWave-controlled thermostat in my home. I love it, and I can adjust it from anywhere I have an internet connection.

When our house is empty, we adjust the thermostat so that it doesn't use as much energy. The scene I've set up for "leaving the house" turns off all the lights, and sets the heat to 65 and AC to 80.

I'd like to hear an explanation for why this is more energy efficient than leaving it at a consistent temperature.

Obviously there are a lot of factors here, like outside temperature and how well the house is insulated, but is it always better to turn the temp down and ask the system to run a little longer than it normally would when you get back in?

If there's a thread where this has been sufficiently explained, I'd be perfectly happy with a link, but if someone wanted to explain again that would be great too.