Why not just turn down the existing thermostat when you leave the house or go to bed? Then turn it back up when you get home or get up in the morning? The savings would be immediate and you would save the $40 to $100 on the new 'stat. I put in a programable 'stat about 5 years ago and found that if I wanted to sleep in, the house was warming up before I wanted to get up, or if I was away at work a few extra hours, the house warmed up too soon. So I finally started to use the "hold" function on the 'stat all the time, which is the same as if I would never had installed the programable one in the first place!