Why do freezers produce so much heat

In March of 2008, I retired my 10 year old 22 ft^3 chest freezer and replaced it with these two new smaller 5.5 ft^3t chest freezers.

Why Two?

When I retired my old freezer, I was aware that I only needed about 10 ft^3 of freezer storage. I could have purchased a single 10 ft^3 chest freezer for less than the two 5.5 ft^3 chest freezers that I purchased. Furthermore, a single 10 ft^3 chest freezer would be more efficient due to its higher ratio of volume to surface area. So did I make the right choice? In the remainder of this article I hope to convince you that I did. Why are two freezers better than one? There are four reasons I can think of:

1. Maneuverability

The only place I can easily fit a large freezer is in our garage which is outside the building envelope (ie it’s unheated and uninsulated). The smaller freezers, however can easily be maneuvered into the house. We heat our home with electric space heaters (see Convert from Gas to Electric Space Heating to learn why). Our heating season is about 6 months of the year. Freezers, like all electrical appliances, produce heat. It takes the same amount of electricity to produce a given amount of heat whether that heat is generated by an electric space heater, or a freezer, or any other electrical appliance.  Therefore, moving the freezers inside effectively reduces the operating cost to zero for 6 months of the year when the heat produced by the freezers offsets the heat produced by our space heaters. If I had purchased a single larger freezer, I would have had to keep it in the unheated garage and pay for its operation a full 12 months of the year.

2. Versatility

The amount of freezer space we need varies throughout the year. During the summer months, one 5.5 ft^3 freezer is plenty. We need the extra 5.5 ft^3 just before winter when we preserve various foods we’ve harvested or purchased. With two freezers, we can simply unplug one during the summer months. The cost of operating the two freezers during the 6 month heating season is zero for reasons described above, and during the other six months, only one of the freezers needs to be operated. Thus the annual operating cost of the two small freezers is only around 25% of a larger freezer of equivalent total volume.

3. Ease of cleaning

It is much easier to clean out or defrost freezers when you have two of them. In the summer when one freezer is empty, contents can be transferred from one to the other making it easy to clean and/or defrost the freezers. It is also much easier to move a small freezer to clean around it.

4. Redundant backup

If either freezer should fail in the summer, we can move the contents into the other. If either freezer should fail in the winter when both freezers are operating, we can move the most important contents into the working freezer.

Cost Comparison

Using a kill-a-watt meter, I measured the performance of the old and new freezers. I also estimated the performance of the 10 ft^3 freezer I was also considering.

22 ft^3 freezer

  • 63.3 kWh over 528 hours = 119.9 Watts continuous
  • 5.45 Watts per ft^3
  • 1050 kWh per year running continuously
  • $0 to purchase (since I already had it)
  • $73.50 per year running continuously ($0.07 per kWh)

10 ft^3 freezer

  • 30 Watts continuous (estimated)
  • 3 Watts per ft^3
  • 262.8 kWh per year running continuously
  • $418 to purchase
  • $18.40 per year running continuously ($0.07 per kWh)

two 5.5 ft^3 freezers

  • 18.2 kWh over 526 hours = 34.6 Watts continuous
  • 3.15 Watts per ft^3
  • 303 kWh per year if run continuously
  • $496 to purchase
  • $21.22 per year if run continuously
  • $5.30 actual cost per year (1 freezer for 6 months since operation offsets heating at all other times)

Payback Calculations

I won’t go into details, but it is not a difficult matter to do an NPV (net present value) analysis given the above information. Assuming a 3.5% interest rate (typical savings account), the cumulative cost (purchase price plus operating costs) in today’s dollars of the three options are as follows:

 

Year22 ft^210 ft^3two 5.5 ft^3
1$ 71.01$ 421.64$ 484.35
2$ 139.63$ 438.82$ 489.30
3$ 205.92$ 455.41$ 494.08
4$ 269.97$ 471.45$ 498.69
5$ 331.86$ 486.94$ 503.16
6$ 391.65$ 501.91$ 507.47
7$ 449.42$ 516.37$ 511.63
8$ 505.24$ 530.35$ 515.66
9$ 559.16$ 543.85$ 519.55
10$ 611.27$ 556.89$ 523.31

It can be seen that by year 7, the 5.5 ft^3 option has a lower cumulative cost than the 10 ft^3 option. By year 9 both the 10 ft^3 and 5.5 ft^3 options have a lower cumulative cost than the 22 ft^3 option. In other words both the 10 ft^3 or 5.5 ft^3 options pay back in about 9 years. However, after that the 5.5 ft^3 option pays back more.

Aside

All electrical appliances produce heat. If you are heating your home with electricity, it doesn’t matter whether the heat is generated by an electric space heater, or a freezer, or a computer, or any other electrical appliance. You will consume the same amount of electricity to produce the same amount of heat. So if you’re going to use the electricity for heating anyway, you might as well do something more useful with it first. Operating a deep freeze is just one possibility. You might also consider growing some of your own food indoors using grow lamps, or doing more cooking and baking in the winter months.