April 23, 2012

Energy Costs versus House Age

Modern homes are built in more energy efficient ways.   New homes usually have better insulation, more energy efficient double pain windows, more efficient furnaces or air conditioners and other energy efficient improvements over older houses.   It then only stands to reason that newer homes should be cheaper to heat and cool. 

Of course newer homes are often larger than older homes so some of that efficiency gets masked by the higher energy costs of a larger home.   Therefore the best way to compare the energy efficiency based on age and improved building practices is by the average cost per square foot.

I found information on average energy spending per homes from the US Energy Information Administration and they broke it down into the decade the home was built.   The numbers are from 2005 which is the most recent covering this information.

Here's the data :


Year of Construction $ / sq ft
Before 1940 0.88
1940 to 1949 0.88
1950 to 1959 0.86
1960 to 1969 0.90
1970 to 1979 0.89
1980 to 1989 0.85
1990 to 1999 0.76
2000 to 2005 0.68


Interestingly there aren't t major differences in the amount spent on the homes from 1940 to 1979.   It seems that the biggest efficiency improvements kicked in after the 1980's. 

If you were looking at a home built in the 1960's versus one built after 2000 then you could expect to see about a 24% decrease in average energy expenditures.

I should point out that this analysis is not perfect since this is just the amount people spent and not necessarily an indication of the different quality of home building per decade.   In other words its feasible that people who own older homes are more likely to waste energy or something like that.   I haven't proven a cause - effect here.   Also the data doesn't take into account other variables such as who owns the homes, where they are built, etc.  Its also possible that more of the new homes are built in states with lower energy costs.   However I think its pretty reasonable to take national spending averages and then assume that the differences are related to building practices based on building age.  

It should also be noted that these are just national averages and individual spending will vary greatly in different climates and other factors.    

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3 comments:

  1. Oil prices (and therefore home heating and cooling costs) jumped in the late 1970's. Remember Jimmy Carter?

    I guess we became more aware of efficiency when prices rose.

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  2. A larger house would have a ratio of square feet to exterior surfaces. Especially if it is multiple floors. Most energy expenditures are on heating and most heat loss is through external surfaces. This would be another reason for the later built -> larger -> lower energy cost per square foot trend.

    On the other hand: My own house was built in the 60's, with an addition in the 90's. There is one spot in the house where you can see a wall that was extended. The later wall is a full two inches thicker than the earlier. I have to imagine that a 33% to 50% thicker wall, insulated from the start with more modern insulation technology, has a far higher R-value.

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  3. Mark : Yes the push for energy savings and energy efficiency really started in the 70's after the oil embargo.

    SteveD : Good point about the sq foot size vs external walls. Newer homes are generally larger on average and should have little more efficiency on sq ft basis.

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