credit: colemama

True or False?

• Cranking the thermostat up ten degrees makes the house heat faster than turning it up two degrees.
• You waste as much energy re-heating the house with a programmable thermostat as you do just keeping it warm all day.
• Most of the energy wasted on re-heating a cool house goes into warming the walls and surfaces.

Answer:

False. False. False. False. False. (Two extra falses to prove the falseness of all of these falsities.)

I hear arguments like these from lots of people, even energy managers and HVAC people, and I just don’t know where the information came from.

Tom Harrison, over at Five Percent, unpacks these myths and gives you the breakdown on how you should REALLY think of your thermostat and home heating system.  He uses a great analogy of a leaky beach ball to demonstrate why programmable thermostats can actually save you energy:

Heating your house is like pumping up a leaky beach ball.

At first, it’s easy.  As the ball gets fuller, the air leaks out faster, so it’s harder to get to “full”. Once it’s full, you still have to keep pumping it up since air leaks out. If you stop pumping the air still leaks out — quickly at first, and more slowly as the ball gets flatter.

So in this silly analogy, a full beach ball is a warm house. Pumping uses energy, like the furnace. The leak represents the way your walls actually work, some are better or worse at slowing down the rate of heat loss, but they all leak.

It makes sense, then, that letting the house cool down means the heat leaks out more slowly, and the total amount of energy it consumes over the course of a day is less than if you kept it warm 24/7.  A house with a programmable thermostat is a beach ball where the pump is on a timer, and the ball is only full when you’re ready to play.

I like it!  And it’s good information as we enter the heating season.  Just be careful about which thermostat you buy if you have a heat pump… it could cost you big.

Can't get enough? Try these related posts:

1. How to Calculate Energy Savings in a Building
2. Beware the Heat Pump Thermostat
3. Home Energy Upgrades: What Should I Do Next?
4. Tools of the (Energy Nerd) Trade
5. Man vs. Machine