How to Calculate Power Savings

Compact fluorescent bulbs, though more expensive than incandenscent bulbs, may be cheaper in the long run.

Numerous electrical appliances and devices are marketed as being "energy efficient." These products are typically more expensive than their conventional counterparts, but they promise long-term savings that compensate for the initial cost. In reality, the amount of savings depends on how you use the device and on the cost of electricity in your area; it may take only a few months to make up the initial expense, or it may take years. A few simple calculations will allow you to determine the power savings for your particular situation.

Instructions

1. Determine the typical power consumption of the two devices you want to compare. This number should have "Watts" as a unit. It is usually printed directly on the device, but you may have to look on the packaging materials or in the instruction manual. As an example, an old electric space heater consumes 1500 Watts, and a new energy-efficient product (with comparable heating ability) consumes 1200 Watts.

2. Multiply the power consumption of the devices by the number of hours they are used per day. The electric space heaters are needed to keep a corner bedroom warm on winter nights, so they are only active for 7 hours per day. 1500 x 7 = 10500 Watt-hours, and 1200 x 7 = 8400 Watt-hours.

3. Divide the Watt-hour numbers by 1000. This gives you the energy consumption of the devices in kilowatt-hours, or kWh, which is the standard unit of electrical energy used by utility companies. The old heater uses 10.5 kWh per day, and the new heater uses 8.4 kWh per day.

4. Multiply the kWh per day by the approximate number of days per year that the devices are used. This tells you how many kWh the devices consume per year. In the example, the heaters are only needed when the night temperature is below 25 degrees. This occurs about 60 times per year, so the old heater uses 10.5 x 60 = 630 kWh per year, and the new heater uses 8.4 x 60 = 504 kWh per year.

5. Multiply these kWh numbers by the electricity rate in your area. This rate is usually given in cents per kWh. You can usually find this information on your electric bill; if not, ask your utility company. A typical electric rate is 10 cents per kWh. In the example, the old heater costs 630 x 0.1 = $63 per year, and the new heater costs 504 x 0.1 = $50.40 per year, so the energy efficient heater saves about $13 per year.

Tips & Warnings

• This general process can be used to calculate the savings in any situation involving different amounts of electric energy consumption. For example, you can calculate how much you would save by setting the heater to "low" instead of "high."

References

• University of North Carolina at Chapel Hill: A Dictionary of Units of Measurement

Resources

• University of Illinois Physics Department: Watts vs kWh