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Summer ended in a hurry and it is almost sweater time!  It was just last month when I wrote the post "Why does programming your thermostat save energy" while focusing on controlling cooling costs using a programmable thermostat.  In that post, I stated the following in regards to how heat enters your home in the summer:

...as the change in temperature (delta T = T1 – T2) increases, so will the heat flow.  In other words, heat is going to enter your home quicker if there is a big difference between the outside air temperature and the inside temperature in your home that is controlled by your air conditioner. If you turn your air conditioner down so your home is cooler, you are increasing the delta T (change in temperature between outside and inside) and the heat will flow into your home quicker, thus forcing your air conditioner to work harder to keep it at the set temperature.

When you heat your home in the winter, you just have to reverse the direction of the heat flow.  Instead of heat flowing into your home in the summer, heat flows out of your home in the winter.  I tried coming up with a real world analogy for the reason heat enters your home faster in the summer as the temperature differential (delta T) between outside and inside your home gets larger, but I realized my analogies made things harder.  But Tom Harrison and fivepercent.us has a great analogy for heat leaving your home in the winter as the delta T increases:

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.

In Tom's analogy, the increasing pressure in the beach ball (represented by the pumping action) is similar to an increase in delta T between your warm inside air and cool outside air. If it is 32°F outside and you set your thermostat at 80°F, heat (hot air) is going to leak out of your home much faster than if you set your thermostat at 65°F.  Just like air is going to leak out of a fully pumped beach ball faster than air will leak out of a half-pumped up beach ball.

Bottom line whether you are heating or cooling your home: The larger the difference between the outside air temperature (controlled by Mother Nature) and the inside air temperature (controlled by your thermostat) the larger the amount of energy required to heat/cool your home.

The solution: Use your thermostat to bring your home temperature closer to the outside air temperature.

Tom actually has much more great information in his post (and more technical information).  But who really enjoys technical information anyway (aside from energy nerds like me).  The real entertainment comes at the end of Tom's post (and featured below).  If there were an award for "funniest energy video of 2010", Tom's video clip would win it!!!!  Fortunately for Tom he has created a video in a category of 1.