Programmable thermostats are a low-cost, high-impact energy efficiency measure that can be done in one afternoon. Programmable thermostats save energy and money by allowing the homeowner to program heatings or cooling at different times of the day. This means that when everyone is away from home, you can turn the air conditioning/heat down or off -- saving you more money. Many new models also allow you to manage the temperature in your home from your smartphone. This allows the homeowner to turn the air conditioning/heat up just before arriving home, in order to walk into a comfortable home without having to waste money.
Properly using a programmable thermostat can sometimes involve a bit of a learning curve. But, the energy savings you see throughout the year is worth the effort.
Energy Star programmable thermostats are some of the best on the market, and can cost as little as $50 to install.