SISL > 2012 Sustainability in Math Workshop > Activities > Replacing Household Appliances: Refrigerator

Replacing Household Appliances: Refrigerator

Krystyna Stave, UNLV
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In this problem, students compare the energy use of their existing refrigerator with a new refrigerator.

Learning Goals

Helps students make environmentally smart choices.

Helps students make environmentally sound personal choices.

It advances students' literacy around sustainability issues.

Helps students understand data analysis.

Context for Use

Example of making calculations and comparing results.

Description and Teaching Materials

Students use information about energy usage per year to calculate whether they should keep or replace their current refrigerator.

Data needed:

Year of manufacture of current refrigerator
Current year
Expected remaining life of current refrigerator
Cost of new refrigerator
Average cost of energy use per year for old refrigerator
Average cost of energy use per year for new refrigerator

Cost of energy over remaining life of current refrigerator =
Average cost of energy per year for old * Expected remaining life of old

Cost of energy for new refrigerator over same time period =
Avg cost for new * Expected remaining life of old

Difference in energy cost = energy cost of old - energy cost of new

$ savings from changing to a newer, more efficient refrigerator = Cost of new - Diff in energy cost

Please mention that the new refrigerator continues to save money for the rest of its useful life. Additionally, if energy costs go up, so do the savings. See Teaching Notes and Tips below for sites that provide more information for students.

Teaching Notes and Tips

Use the Department of Energy's calculator for savings on energy efficient appliances to enhance the assignment with more sustainability related information.

For refrigerators, see

For a list of other calculators, see

For a way to calculate greenhouse gas pollution from your home instead of just dollar savings, see


References and Resources