Question: Is it cheaper to have your thermostat turned down when you are out of the house and have it come back on when you get home or to keep it at a constant temperature?
Answer: When your house is hotter inside than outside, the energy (heat) will move from areas of higher concentration to lower concentration. The warmer your house is than the outside, the faster this will happen. It’s the same reason why you can boil water faster on a stovetop set to high than a stovetop set to medium-high. The hotter something is (like the burner), the faster heat will flow from the source to the surrounding environment (like the water). You can look up Newton’s Law of Cooling for equations that describe this effect.
When you keep the house warm all day, you leak heat outside at a constant rate. The only way to leak heat faster is if you heat the house above room temperature. If you turn down your heat when you’re gone, at first the heat leaks at the same rate as a heated house, but as the house cools the rate of heat leaking will slow down simply because there is less of a temperature difference between outside and inside. When you need to reheat the cold house, it doesn’t matter that it might feel like you are using a lot of energy, as you bring the temperature of the house up you are always leaking heat at a slower rate than if you kept it that temperature the entire time.
The amount of energy it takes to bring your house from cold to warm is less than the amount of energy required to keep it warm all day. To save money and energy, install a programmable thermostat. A programmable thermostat can be set to lower the temperature while you’re away (at work) and will bring your home back to a comfortable temperature when you return.