Does Turning Down the Thermostat Realling Save Money?

I have been doing some reading on this topic and have noticed that authors tend to gloss over the facts here and just say, "Oh yes turn down the thermostat...it is good for you!"  My mom said the same thing about broccoli, I wasn't convinced in either case.  Unfortunately the value of broccoli was not covered in any of my college courses, so mom is going to need to do her own research, but CONDUCTION was covered and it's the basic concept we need, to help us understand what is going on with temperature differential and home heating.

How to Calculate Energy Loss in the Home

First I want to provide a link to a nice article on eHow about measuring your whole house and analyzing the energy loss.  http://www.ehow.com/how_5556053_calculate-heat-loss-home.html

It is a little mathy and probably too time consuming for any normal person to want to embark on, but if you must know, measure away!

Personally I went after it with just a square meter of window to get the idea without the hard work.  

Let's just take a square meter of window and an arbitrary thickness of 5 mm for a single pane of glass.  Without any of the thermal layers or convection considered we are looking at about a 3% reduction in heat transfer per degree Celsius.  Here is a nice spread sheet from our government energy saving web site.  You tax dollars at work!  Energy Spread Sheet.

What we want to calculate is the amount of energy we are taking from the inside of our house and dumping outside each second.  This is the RATE of loss which is what all the cool kid equations provide.

How to Get a 3%+ Savings By Turning Down the Thermostat

I was a little dubious of the 3% number, which I was surprise to see falls in line with many other documents that talk about this topic.  I just ran it right out of the book example and dropped it into my own spread sheet.  When I increased the glass thickness, I have double pane glass, the good news was that the % reduction was about the same, but the energy loss rate was about 1/2, just what you would expect.  Hurray for double pane glass.  I also have gas filled window panes, which also have a minor effect on the transfer rate.  Not worth doing the math for here.  

Thanks go out to our buddy Fourier who did the work to figure out that heat transfer from two things of different temperatures sitting next to each other was a function of the difference in temperature, the thickness, and some relationship between the two objects for how good they are at moving heat back and forth.  Nice fella, Fourier.

So, give or take a lie or two, consider a 3% savings RATE when you drop the thermostat one degree Celsius.  Consider the amount of time the house is at that new rate, 8 hours while you are work would be 1/3 total time so about 1% actual savings per degree for an 8 hour period.

Ok, I know what you are asking yourself.  How much does it cost to bring the temperature back up after I let it drop down a few degrees?  Am I really saving money?

We will tackle that one in another article.