NAME: _______________________________________ DATE: _____________
CLASS: ______________
HOME ENERGY AUDIT: ENERGY EFFICIENCY WORKSHEET
Calculating Lifecycle Costs—How much will an appliance
cost to buy and use over a lifetime?

purchase price 
+ 
(annual energy cost x estimated lifetime x discount factor) 
= 
lifecycle cost 

APPLIANCE 
ESTIMATED LIFETIME (years) 
DISCOUNT FACTOR 
water heater 
13 
.83 
refrigerators and freezers 
20 
.76 
room air conditioner 
15 
.81 
dishwasher 
12 
.84 
clothes washer 
18 
.78 
Calculating Payback Period—How long will it take to
recover the extra money you spend for a more efficient appliance?

purchase price of more expensive model 
 
purchase price of less expensive model 
= 
difference in purchase price 

higher yearly operating cost 
 
lower annual operating cost 
= 
difference in annual operating cost 
difference in purchase price / difference in
annual operating cost = payback period

Example: You are shopping for a refrigerator. There
are two models. One casts $100 more than the other but saves
$25 per year in electricity costs. Which refigerator should you
buy?


$1000 
purchase price of more expensive model 

 
$900 
purchase price of less expensive model 

= 
$100 
difference in purchase price 
$100 / $25 savings
in electricity costs/year = 4 years
It would take 4 years to realize the savings. However, since
the payback period is only 4 years and your refrigerator will
last much longer than that, you will save money over the life
of the rerigerator and conserve natural resources.
Problems:
You would like to buy a new refrigerator and are looking
at two different models.
1. If model A uses 700 kWh/year, how much is the yearly operating
cost (based on a cost of $.089 per kWh)?
700 kWh/year x $.89 /kWh = $62.30
2. What is the lifecycle cost of model A if it cost $789?
lifecycle cost = purchase price + (yearly operating cost x estimated lifetime x discount factor)
yearly operating cost x estimated lifetime x discount factor = $62.30 x 20y x .76 = $946.96
$789.00 + $946.96 = $1,735.96
3. If model B uses 900 kWh/year, how much is the yearly operating
cost (based on a cost of $.089 per kWh)?
900 kWh/year x $.089 /kWh = $80.10
4. What is the Lifecycle cost of Model B?
($80.10 x 20y x.76) = $1217.52
$700.00 + $1217.52 = $1,917.52
5. If model A costs $789 to buy and model B costs only $700,
what is the payback period?
(Difference in purchase price) / (Difference in annual operating cost) = payback period
$89.00 / $17.80 = 5 year payback period
