Ames Electric Department

Estimating Energy Savings

Saving Energy is Important
Undertaking a program to improve your home's efficiency is a good thing.  It can lower your utility bill, contribute to a lower electric rate and help protect our environment.  However, estimating how much you save can be difficult and confusing.  

How can we estimate how much we save and  when is it worth our investment to make changes?  Fortunately, there are some numbers that we can use as a guide.  To figure your savings you'll need two things: 1. Annual dollars spent on heating and cooling, and 2. An estimate of base load dollars.  You can get this information from copies of your past year's utility bills.  

Base Load Dollars
Base load dollars is the amount of energy (less services charges) used during non heating and cooling months.  Typically this would be the "shoulder" months for cooling.  Shoulder months are those when no cooling is needed and no additional fan energy is used.  For your base load electric dollars, average March and October.  For your base load heating (gas) dollars, average July and August.  Take these numbers times 12.  You now have a heating base load and cooling base load dollar number.  

To estimate your annual heating dollars, add the past year's heating bills (less service charges) and subtract your heating base load dollar number.  To get your cooling dollars, add the past years electric bills (less service charges) and subtract your electric base load dollar number.  

EXAMPLE: Based on January through December, 2000 bills the following data was gathered. These dollars do not include service charges.

Month	Electric	Gas
January	$48	$110
February	$37	$108
March	$33	$88
April	$41	$55
May	$44	$42
June	$59	$38
July	$89	$33
August	$80	$34
September	$52	$51
October	$33	$76
November	$34	$98
December	$51	$107
A.                          Total	$600	$841
B.  ((Mar + Oct)/2)  x 12	$396
C.     ((Jul + Aug)/2) x 12		$402
Heating Total (A. - C.)		$439
Cooling Total (A. - B.)	$204

In this example, we averaged March and October to determine the annual cost of electricity this home uses outside of cooling ($204).  We averaged July and August to determine the annual cost of gas the home uses outside of heating ($439).  NOTE:  These are rough numbers, but serviceable for your analysis.

Savings Calculations for Common Efficiency Improvements
Once you know approximately how much you spend on your heating and cooling, you can begin to understand the impact of making energy efficiency changes to your home.  

The following are rough guidelines to help you estimate savings.  They are presented as annual percentages and are based on national averages.  To determine your savings, apply the listed percent savings to your appropriate annual energy cost.