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NC State Extension

Cumulative Savings – Defined

Sum of the total annual energy savings over a certain time frame. (For example, if we install a measure for each of two years, the cumulative savings would be the sum of the measure installed in the first year, plus the incremental savings from the savings installed in the second year plus the savings in the second year from the measure installed in the first year.)

Figuring out the TOTAL SAVINGS and TOTAL COST of a project:

Example 1:  Air Sealing Duct Work – If an air-sealing project is determined to cost you $100 to complete as a DIY and is estimated to save you $10/month in energy savings, you will have paid for the project in 10 months and will continue to save $10/month into the future.

  • Initial Cost                                     $100
  • Months to recover cost                  10
  • Annual savings                              $120/yr
  • Amount saved after 1 year             $20       (Savings – Cost)
  • Amount saved after 5 years           $500     (Savings – Cost)
  • Amount saved after 10 years     $1,100   (Savings – Cost)


Example 2:  Installing 20 Energy Star CFL light bulbs in place of incandescent bulbs – The bulbs will cost about $56 and will save approximately 83%. Each year you will save approximately 1,358 kWh of electricity and $153. Over the life of the light bulbs you will save approximately $954 in electricity costs and $48 in equipment replacement costs. By choosing ENERGY STAR you will reduce emissions by approximately 2,091 pounds of carbon dioxide annually, which is equivalent to the emissions reduction of not driving your car for 72 days.

  • Initial Cost                                                             $ 56
  • Months to recover cost                                          4
  • Annual Savings                                                     $ 153
  • Amount saved after 1 year                                     $ 97     (Savings – Cost)
  • Amount saved after 5 years                                   $ 612   (Savings – Cost)
  • Equipment Life Cycle                                            7.3 years
  • Life Cycle Savings in electricity                                          $ 954
  • Life Cycle Savings in equipment replacement costs          $ 48
  • Total Savings over lifetime of bulbs                        $ 1,002

Additional questions to ask yourself when setting priorities for projects:

  • Which of these projects will add the most value to my home?
  • How long do I plan to own my home?
  • I am a renter. What projects make sense for me? (See Resources for Renters)
  • I have identified some comfort issues in my home such as drafts. Which of these projects will most effectively add to the comfort of my home?