Questions & answers about refrigerator energy use

Last update: July 2012

This page is only Q&A and some technical data.  If you're looking for general info on refrigerator energy use, see my main Refrigerators page, which includes the Refrigerator Energy Calculator.

I think we can help the coils get rid of heat better by spritzing them with water when the motor is running and the coils are very hot.  I can tell it works because of the steam that comes off and because the motor shuts off quicker.  (Yes, i know it opens up a wealth of issues, like the danger of electrocuting yourself if you have bad wiring, or eventually building up sediment from hard water, so of course all this has to be underscored with common sense.) I am simply stating that there is a lot we can do to help coils get rid of heat. —Yosh Hash

I'm always happy when readers come up with creative ways to save energy, though I have to tell you that this won't save much energy.  If you air-condition your home, your AC will ultimately be removing the same amount of heat anyway, just over a different period of time, so there's no savings to be had there.  And if you don't air-condition your kitchen, you could see some savings, but the amount won't be very much.  A modern fridge uses only about 50 kWh per month, and if you were able to reduce that by 10% (which would be very optimistic), we're talking a savings of only 5 kWh/mo., or $0.80/month. at 16¢/kWh.

I don't know why the manufactures don't make a detachable unit so that the coil can be put somewhere cool while the fridge itself stays in the kitchen. —Yosh Hash

Your idea is that it's easier (more efficient) for a fridge to get rid of its heat in a cooler place.  A different advantage is that if you exhaust the heat to outside the house in the summer, you won't be paying to remove that heat with your air conditioner.

That's nice in theory, but in practical terms there's no savings to be had, because such a fridge would be more complex and cost more, not to mention requiring more maintenance.  Even if there were no extra equipment costs, the extra heat added to your home just isn't that great.  Finally, most consumers want something simple and hassle-free, and a multi-unit refrigerator is the opposite of that.

Here's the math on the lack of savings:  A modern fridge uses about 600 kWh a year, or 50 kWh per month.  If 100% of that energy were turned into heat, then at the rate of 1000 kWh per 3.41 million therms (source), your fridge puts out 50 kWh x 3.41M therms ÷ 1000 kWh= 170,500 therms per month.  A 13-SEER AC would use 170,500 ÷ 13 = 13,115 watt-hours to remove that heat, or about 13 kWh.  At 16¢ per kWh, you're paying a whopping $2.08/mo. to remove that heat during the summer.  A more energy-efficient AC costs even less to run.  And during the winter, the fridge is actually helping heat your home, so you use less energy for heating, which compensates for the extra you spend in the summer.  So the payoff from putting the condensing unit outside just isn't there.

That's not to say that capturing the heat from the fridge and using it elsewhere hasn't been tried.  It has. (see PDF)

If any reader knows of a commercially-available fridge with a separate condensing unit, then by all means please let me know.

How many hours a day does the compressor in the fridge run, on average? -- Spiney Norman, June 2008

Interesting question. My fridge uses 143 watts when the compressor runs and 0 watts when it doesn't. From the table above, a modern fridge uses about 500 kWh a year. On a daily basis that's 500 kWh / 365.25 days = 1.37 kWh a day, or 1370 watt-hours. 1370 Wh / 143 W = 9.6 hours/day. Of course, if you don't heat or cool your home much like me then it will run more in the summer and less in the winter, but this is a pretty good estimate.

What is this number useful for? Well, say you wanted to compare the cost of leaving the door of your fridge open all the time to something else, like I do on the cooling page. For that you'd need to know how many extra hours a day the compressor runs (which we've calculated to be 24 - 9.6 = 14.4 hours), or at least what percentage of time the compressor runs (which would be 9.6 / 24 = 40%).

I live in a house with four other people. Recently they've been eating my food. I was thinking about putting my food in a metal box with a lock on it (extreme I know). A friend told me that I shouldn't do this because it would require more energy for the fridge to cool down. But that doesn't seem right to me. Metal cools very easily and stays cool very easily, so it would seem to me that besides being a little annoying it shouldnt be a problem. Who is right? -- Lee-Ana, Santa Cruz, CA, Jan. 2005

That's really funny. Reminds me when I was in college and a housemate would spit in his Kool-Aid so nobody else would drink it.

To answer your question: you're right, your friend is wrong.  What refrigerators do is to extract heat from things.  Technically they don't insert coldness, what they do is to suck out the heat.  When you put a bunch of your room-temperature groceries in your fridge the fridge starts sucking the heat out of them and sending that heat to the coils on the back or the bottom of the fridge.  It takes the heat that's on the inside and sends it to the outside.

Putting a room-temperature metal box in the fridge is no different from putting a room-temperature bag of carrots in the fridge. The fridge is gonna suck the heat out of both objects and send it to the outside of the fridge. Once either object has had its heat removed it doesn't take any extra energy to keep it cool, because its heat has already been extracted. When the fridge runs after it's cooled the contents, it's because of heat entering the fridge from the outside (slowly seeping through the walls of the fridge, or through the door when you open it.) Hope this helps.

I am looking to purchase a new refrigerator and cannot find out how many watts of power it uses.  It has an Energy Star rating with a high and a low rating in kWh/year from 578 to 732 according to its Energy Star tag.  How do I find out from the Energy Star tag how many watts it uses?  Should I guess that it means 578 to 732 watts?-- David, Dec. 2004

You just need to read a little more carefully. The label does not say that the fridge has a high and low rating in kWh/year of 578 to 732. What it actually says, in large, bold, reverse type, is "Energy use (kWh/year) range of all similar models." This means the most efficient competing fridge in the same class as the one you want to buy uses 578 kWh year, while the least efficient uses 732.

The model you're looking at uses 607 kWh/year. I know this because it says so right on the label (in large, bold type, right above the range listed above). This fridge is therefore one of the most efficient in its class since it uses less than similar models.  Of course you've chosen the least efficient style—as mentioned above, side-by-side models use more energy than either top-freezer or bottom-freezer models.

If you want to know how many watts the fridge uses while the compressor is running, you can't find that from the Energy Star label (you'd have to look at the fridge itself), but then again I'm not sure why you'd want to since that information is fairly useless. The label tells you the kWh/yr., and how many kWh/yr. other fridges use. That's what you need to know.

I have a 12v fridge which uses 3.5 amps when running, or 42 watts. This seems like a fraction of what my 240v small fridge downstairs uses. Factoring in the inefficiency of my 4amp rectifier at say 70%, it seems that the 12V fridge uses less power than the 240v fridge. Is that right? —Paul O'Kane, Brisbane, Australia, Dec. 2004

Well, you didn't tell me how much power your 240V fridge uses, in either amps or watts, so it's kind of hard to compare. I also don't know how big each fridge is, or how old each one is. You haven't given me much to go on. You could easily measure the electrical use of each unit to get a good and accurate comparison yourself. You have access to the equipment, but me sitting over here on the other side of the planet without even a good idea of what kind of equipment you're running, I'm just guessing. But as long as I'm guessing, let me guess that the key here is that the 12v fridge uses less power when running, but that it has to run longer to chill an equivalent amount of space compared to the 240V fridge.

Can I save energy by putting my refrigerator or freezer outside in the winter? —Marty Siller, Oct. 2004

You can put your freezer outside as long as the temperature is usually above 0 degrees F. You can't put your fridge outside, though. Well, you can, but your food will spoil.

When the ambient temperature is too low your fridge gets confused and so it doesn't run the compressor as long as it should. That means that the temperature inside the fridge winds up being too warm. A General Electric manual I just checked said not to run the fridge when the ambient temperature is below 60 degrees F.

Freezers are more forgiving, since they cool to a lower temperature. A GE freezer manual says that the freezer will work fine with ambient temperatures as low as 0 degrees F.

Appliances vary, so check your own owner's manual to see what your equipment's temperature tolerance is before you try this.

In order to save electricity, is it safe to turn off the refrigerator/freezer before going to bed and turning them back on in the morning? I would like to know if doing this may damage the appliance. —P.M. Vasquez

This won't save any electricity. As soon as you turn the fridge back on, it will run a bit longer to get the temperature back down to normal. If you turn the fridge off at night then you might keep the compressor running for 60 minutes throughout the night, over several start-stop sessions, but when you turn it on again then it will simply run for 60 minutes all at once.

Careful readers have wondered why this contradicts my advice for air conditioners, where I say that it uses more energy to keep the AC on during the day than to just turn it on when you get home. They question why my fridge answer wouldn't work the same for the house: aren't we just delaying the heat-removal process until later, rather than reducing it?

It's a good question, and here's why it's different: A constantly-cooled fridge (overnight, with the door closed) is just not the same kind of heat magnet that a constantly-cooled house is. The whole fridge is sealed and insulated and is sitting in a house that's probably itself air-conditioned down to 80°F or lower. So constantly cooling the fridge doesn't let appreciably more heat enter than turning it off overnight and having it remove the accumulated heat in the morning.

I plan to confirm this by testing when I get a chance and report the results. In the meantime, I hope readers will do their own tests with a Kill-A-Watt meter, running the fridge for a few nights normally and then running it for a few nights with it off at night and then share the results with me.

My boyfriend believes that if we keep several jugs of water in the freezer and in the refrigerator that it will keep the cost of electric down.... Does this really work? —Angie Stanton, Feb. 2004

Sheesh, boyfriends will believe anything. Okay, technically the answer is "it depends", but for all practical purposes the answer is "no".

When you open the fridge cold air gets out and warm air gets in. If your fridge is full of water jugs then there's less room for warm air to rush in and occupy, so your fridge can cool back down to the proper temperature quicker. But a fridge full of food serves the same purpose, and most people's fridges are already pretty full. The only way adding water jugs would save much energy would be if your fridge is usually fairly empty and you open the door frequently -- but if the fridge doesn't have much food in it then why would you be opening the door so much? So the bottom line is, it's not really going to make an appreciable difference.

By the way, when you're ready to upgrade to a boyfriend who knows about refrigerators then drop me a line again.

Sources & Technical Data

• <1976 -- 1800 kWh
• 1976-86 -- 1400 kWh
• 1987-89 -- 950 kWh
• 1990-92 -- 900 kWh
• 1993-00 -- 700 kWh
• 2001+ 500 kwH
• Energy Star 2001-04 -- 450 kWh (10% better than 2001+)
• Energy Star 2004-08 -- 425 kWh (15% better than 2001+)
• Energy Star 2008-10 -- 400 kWh (20% better than 2001+)
  
• CEE Tier 3 -- 350 kWh (30% better than 2001+)