Energy Efficient Freezer: Should you replace your old freezer?

The energy efficient freezer question – should you purchase a new freezer and get rid of the one you've had for years? The energy consumption of appliances makes up a large portion of our monthly electric bill so it makes sense to seriously consider the common, though oversimplified advice, “If it's more than 10 years old, it's time to replace it with a new, energy efficient model.”

We recently looked at the possibility of replacing our aging upright freezer. Before making the investment in a new appliance, we decided to take some real measurements of the energy our old model was using. You may be surprised by what we discovered and the decision we made regarding purchasing a new efficient model.


The Quest for an Energy Efficient Freezer

We've probably all heard the advice in the media advising that if you have an older refrigerator or freezer, you should seriously consider replacing it since newer models are so much more energy efficient.

As a blanket statement, it's probably good advice if your appliance is in the twenty year old range, but I've seen articles suggesting that units as young as ten years should be replaced.

When I started looking critically at our twelve-plus year old upright freezer, I did wonder how much we were spending to feed the little guy. I was certain that more efficient models are currently available, but would the resulting savings really be worth the investment? Just how long would it take for the new unit to pay for itself?

Then it hit me – Hey, that's what I do!

Energy Efficient Freezer: Using the P3 International Kill A Watt meter

Fortunately, I had a Kill-a-Watt meter in my office (actually, we have several of these great little gadgets).

These meters allow anyone to enter their local electrical rate per killowat hour, then plug a 110v (up to a 15 amp load) appliance into the outlet on the unit to collect real-time data on what the device is costing you to operate.

There are a number of similar meters on the market, but I prefer the Kill a Watt for the price and the number of features the Kill a Watt offers.

Programming and use is truly simple and the included instructions are complete, though you could probably figure it out with a little fiddling without ever opening the manual.

For larger appliances such as freezers or refrigerators, I use a three foot appliance extension cord so the meter can be left in place for a while with the appliance in its normal resting spot, all while placing the Kill a Watt where it can be read.

Be certain that you use an extension cord that is at least as heavy as the cord on whatever appliance you are testing.

When collecting data on a household appliance such as a freezer, it is important to get a fair sampling of usage. If you plug in a freezer for just a moment, the meter will give you a reading, but that reading may look either extremely low if the compressor is off the whole time you test, or super-high if the compressor is on for the few moments that you collect data. If you happen to catch your appliance while the automatic defrost is operating, the numbers will really scare you.

To get an accurate reading, let the appliance run through the meter for a few days to get a true representation of usage patterns.

In the case of a refrigerator or freezer, energy consumption will vary according to how often the appliance door is opened, how long the door is open at a time, the temperature of any food that is added, how full the unit is, how often the auto defrost (if equipped) operates, and the temperature of the room.

A longer metering time will give a more accurate reading by averaging these fluctuations.

Energy Efficient Freezer: Taking Some Measurements

As I walked through a local appliance retailer recently, I spotted a brand new energy efficient freezer (it said so right on the tag) of the same size and similar design compared to our elderly little freezer. This unit sported an EnergyStar label along with a yellow EnergyGuide reporting an average energy cost of $56 a year. I ran home and hooked our freezer to a Kill A Watt meter to see how it compared.

After a week of metering, I discovered that our freezer is costing us about $76.28 per year to operate. At an energy savings of nearly $20 per year it was a little hard to justify a $623 expenditure for a new appliance.

Hey, wait a minute—those EnergyGuide estimates are based on a national average energy cost...

Our energy is far above the national average. Doing the math quickly, I discovered that the new freezer was going to burn approximately $84.13 worth of electricity per year—a whopping $9.85 more per year than our old and tired freezer!

What's going on here?

Energy Efficient Freezer: Making Sense of the Numbers

Full Freezer

Now do I really think that a new freezer with better insulation and modern compressor technology is going to use more electrical energy than our old model? Of course not.

According to the Energy Information Administration and Lawrence Berkley Labs, modern freezers are, on average, nearly three times more efficient than models manufactured before 1990. The development is pretty much linear between the two times, meaning the older the appliance, the more energy it likely consumes.

The reasons for the discrepancy in predicted savings and our measurements could be our own usage patterns in opening and closing the freezer door (ours is rarely opened) the amount of frozen material in the unit (a full freezer stays colder longer without using the compressor, and ours is VERY full) and the temperature differential between the inside of the appliance and the temperature of the room, or the ΔT (Delta-T).

Each of these factors is defined by an average decided upon by the EnergyStar folks.

Our usage varied compared to the EnergyStar test parameters, and yours probably will too.

I have no doubt that a newer freezer will result in some energy savings for us, but the metering exercise illustrates that the savings may not be worthwhile in all cases. I will be replacing the door seal in our old freezer, doing a manual defrost, and expecting years of additional happy service.

It pays to do your research, and maybe a little measuring.

That little P3 Kill A Watt meter, which cost me less than $25, just saved me from making an unnecessary $623 purchase. I use the meters occasionally in my consulting business, but I use them all the time at home to find out just how much energy is being consumed by various items.

Energy Efficient Freezer: Making Your Current Freezer More Efficient

Whether you have a shiny new energy efficient freezer or an older model that is still serviceable, there are a few simple things you can do to increase efficiency and save electricity:

Keep it clean:
Vacuum the dust and other debris from behind the unit and out of any cooling exchangers or other mechanics that you can get to. A freezer must be able to transfer heat from inside the unit to the surrounding air. Dust bunnies are amazingly good insulators and will make any freezer less efficient.

Keep it cool:
Avoid putting a freezer in a hot garage or against a south facing exterior wall. The higher the temperature of the room, the harder a freezer must work to maintain the high ΔT or temperature differential between the inside of the unit and the room air.

Energy efficient freezer

Keep it full:
An empty freezer has less mass to resist thermal swings. If you have a mostly empty freezer, consider raiding your recycle bin for bottles that you can fill with water and freeze.

Keep it (almost) frost-free
Although frost-free freezer and refrigerator systems can be real energy wasters, so can large amounts of built up frost in a freezer. Krigger and Dorsi, in their book Residential Energy, recommend defrosting a freezer any time more than ¼ inch of ice builds up on the walls of the appliance.

Keep only one:
A single big freezer is more efficient than having two smaller units. If you replace a refrigerator or freezer, resist the impulse to move the old unit to a garage corner to keep your occasional overflow food cold. Recycle that baby and enjoy the energy savings.

Energy Efficient Freezer: Upright Freezer vs. Chest Freezer

If you are going to replace your current freezer with a newer unit, what's the most efficient form factor, upright or chest?

Almost without exception, the most energy efficient freezer models are chest units. When you think about it, the primary reason for the efficiency difference is pretty obvious: Cold air is more dense than warm air.

Each time you open the door on an upright freezer, all that cold dense air inside simply seeks the lowest level it can attain, which is on the floor of the room. The cold air that cascades along your floor each time you open your freezer door is replaced with warm room air.

When the lid on a chest freezer is opened, the dense cold air wants to stay right where it is, meaning efficiency is improved.

So, if you are looking for the most energy efficient freezer possible, look closely at a chest freezer.


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