How Can Replacing My Windows Reduce My Utility Bills by 40%?

Have you ever seen a claim that if you replace the windows in your home you can reduce your utility bills by 40%?  How about 60%?  Have you ever thought about how this can be possible?  The truth is, it probably can’t.

A typical homeowner in the St. Louis area spends about $2,500 per year on electricity and gas.  About 45% of that, or $1,125, goes towards heating and cooling the home.  The other 55% goes to things like heating water, washing clothes, and lighting.  And don’t forget the video games.

In the winter time, the furnace runs and produces heat for the house.  Once the house is warmed to the set point on the thermostat, the furnace stops running.  Then, the warm house begins to slowly cool down.

Where did the heat go?

Some of that heated air leaks out of the house through all the cracks and gaps, primarily in the attic and basement or crawlspace.  Some of that heat may leak out through the windows, while a good amount of the heat is conducted out of the house through the walls, ceilings, floors, windows, doors, and other exterior boundaries.  Some heat may have radiated out of the house through windows and other exterior surfaces.

In the summer time, the reverse happens.  The air conditioner cools the house and then shuts down.  Then the house slowly starts to gain heat.  Some of the heat gains enter the building through the windows, whereas some other heat gains enter through all the other exterior boundaries.

How much energy is lost through the windows in my home?

Through summer and winter, the typical St. Louis home has “lost” $1,125 worth of energy.  The question is, how much was lost through the windows?  The answer?  About 10%.  That’s $113 per year.  

Replacing those windows might optimistically save 40% of the 10% lost though the old windows.  40% of $113 would be a savings of $45 per year.

With an annual energy bill of $2,500, a savings of $45 per year is equivalent to saving about 2%.  Saving 40% of the energy that is lost through your windows is a far cry from saving 2% of your total utility bills.