Q: For a household appliance, at what energy differential does it make sense to replace immediately vs. at end of life for the unit?

Asked by Rolf Munson, ’80, Boulder, Colo.


When my housemate’s hankering for breakfast smoothies wakes me up in the morning, I often ask myself a similar question: Can I justify—on energy-efficiency grounds—throwing out the old blender for a new, quieter one? Unfortunately for my sleeping in, replacing even an old blender would not make environmental sense. But, it turns out, replacing an old refrigerator does.

The question of when to replace old appliances really comes down to broad categories of how much energy the appliance uses: “a lot” or “a little.” A new blender may be more than twice as efficient as our current one, but because this household annoyance uses just a fraction of a kilowatt-hour per use, the overall energy savings would still be tiny—about 0.02 percent of an average household’s energy use for the year, and probably less than it takes to manufacture and ship the new blender and dispose of the old one.

On the other hand, feeding the refrigerator’s energy appetite requires a much larger chunk of a household’s yearly electricity bill. In my case, our landlord replaced the fridge right before we moved in, in 2004, so it’s quite new and fairly efficient, though it still accounts for about 12 percent of my apartment energy’s consumption.  If instead we used a typical model (with the freezer on top) from the 1990s, the refrigerator would make up more like 20 percent of our electricity bill. Federal regulations have heightened the energy performance of newer refrigerators, primarily through more efficient compressors and superior insulation.

Overall, if an appliance doesn’t use a lot of energy, replacing it with a more efficient model won’t make much difference in minimizing your total energy use. But deciding which energy-guzzling appliances to replace may not come down to a single benchmark energy differential either. 

Instead, let me propose a general rule, with some important caveats, based on my conversations with energy-efficiency analysts. Think 5-10-15: if the appliance is five years old, do not replace; if it’s 10, run the numbers; if it’s 15, it’s probably time to replace.

This rule works well for five of the top energy suckers in your home: refrigerators, water heaters, central air conditioners, furnaces and clothes washers. Old versions of these are most likely worth replacing and newer ones aren’t. For the decade-old types, the Energy Star website helps you estimate the difference between your current appliance and new, more efficient models. This will give you an idea of how much energy and money you could save with a new appliance, and then you can decide if it’s worth the investment.

The 5-10-15 rule doesn’t work for all large appliances, however. Electric clothes dryers are real energy hogs, and there hasn’t been much room for improvement—most use similar amounts of electricity no matter when they were made. Similarly, the government doesn’t even set efficiency standards for gas and electric ranges—burning energy, after all, is what these appliances are designed to do, although gas ranges are more efficient than electric ones.

So in the end, focus your worry where it can do the most good, and think about whether to replace your refrigerator, water heater, central air conditioner, furnace and clothes washer. That way, if you ever get a prank call asking if your refrigerator is running, you can proudly answer, “Yes, and efficiently!”


Rachel Adams is a PhD candidate in biology.