Practical Numbers

Replacing an old appliance with a new efficient one?

I have dealt with this question a few times in my house.

Our current referigerator is over 10 years old, works great. But I kept wondering if I should buy a new energy efficient referigarator.
So I decided to run the numbers and see how much would I save if I upgrade.
To do this correctly, there are 3 steps:
  1. Shop around for your new appliance, write down the expected annual electrical consumption for that device. It is usually written on a yellow tag that tells you how much it costs to run that device. Don't put to much stock in the $ amount they quote, what you need is the number for Kilowatt-Hour.
  2. Figure out the actual average cost per Kilowatt-Hour in your house. You can probably call your electrical provider to get you your average cost for the last year, or get your past utility bills, write down your total dollar amount for electricity each month, and write down the total Kilowatt-Hour consumed each month. Add up all dollars and divide it by all Kilowatt-Hour, now you have the average cost per Kilowatt-Hour.
  3. Now you have to measure how many Kilowatt-Hour your existing appliance uses. There a few ways to do this. Personally, I purchased a Kill-A-Watt (you can purchase one here). You plug your appliance into this device and it will display how much electricity it uses. Since a refrigerator continously while cycling on and off, you can get the best numbers by getting total consumption for a whole day.

Make sure you are comparing similar consumption periods. If the new appliance has a quote for the whole year, then convert to  per hour (/365 , /24). If you measured your old appliance for a whole day, then divide it by 24.
Since getting the Kill-A-Watt, I have found numerous uses for it. For example, I was able to see how much electricity some appliances use while supposedly off. The biggest cluprit has been the DVR which is not really off. But I also used it to calculate similar comparisons for the washing machine, the TV, and my wine-fridge (which turned out to be using more electricity than both large refrigerators in the house, so it had to go).

1- Your cost $ per kWhr:
Old Appliance New Appliance
2- Total kWhr Measured: 4- Quoted Consumption:
3- Hours Measured: 5- Quoted Hours:
6- Average hours used per Day:
Old cost per year: New cost per year:
Savings per year:

Notes (values between brackets are examples):
1- Average yearly cost per Kilowatt-hour (my 2008 average in California was $0.205)
2- Total kWhr measured (3.31)
3- How many hours did you measure (24)
4- Consumption displayed on new yellow tag (407)
5- Hours for above #3 consumption (407 kWhr per month = 0.0807 kWhr/hr)
6- How many hours will you be using this appliance per day (for a fridge it should be 24, for a washing machine, we use it about 1 load per day, takes half an hour so use 0.5)
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