Program Thermostat or Set and Forget

[Mark Smith]

I just moved into the duplex I am house hacking. I put in a couple 7 day programmable thermostats to take a step toward a more efficient house; each unit only has one thermostat. My question is, which would be more energy efficient: setting the thermostat at 65 and just leaving it, or actually programming it to drop the temperature when I leave and warm it up when I come back? I'm just wondering if it would actually take more energy to bring the place back up to temp than it would to just let it maintain one constant temperature. In case it helps, it is a gas/hot water system.