Hi Reader, is it safe to set your freezer to -70°C?
As I outlined in one of my latest posts, driving change can be simple, especially as more and more companies support the movement.
And one of the first things that comes to mind when we think about sustainability is freezers.
However, many myths exist - among opponents and proponents of the temperature change. So, let’s dive in and look at the actual data.
Today's Lesson: Discussing Change to Our Freezers
Is switching to -70°C a good idea?
Number of the Day
There's so much discussion going on about -80°C, the set temperature of most ULT freezers. But what is so special about this number? In fact, there isn't anything special about it. There isn't a single study or physical principle that would show that storing samples and reagents at -80°C is necessary. It is an absolutely arbitrary number. But the question, of course, is: where does this number come from? In fact, literally nobody knows. But let's discuss this in a little more detail.
80
Increasing Freezing Set-Points
Freezers get a lot of attention because of their high energy consumption.
As I have never seen anyone else doing, I tried to compile the energy consumption of several freezers for you. Please note that the years of release are estimates as precise release dates are barely available. All shown models have a storage volume of 520-590L. Some of the consumption data were mathematically extrapolated, not actually measured.
But here's the first myth that we need to address: many claim that freezers use as much energy as an entire family home.
While for some parts of the world that might be accurate, a US family home consumes 20-35kWh.
Still, what matters most is how we can get our freezers to consume even less:
Quantifying Savings
A case study from the University of California estimates that switching from -80°C to -70°C saves between 15-29%.
Three different freezers: two “conventional” models and one Stirling freezer that, instead of using a typical compressor, relies on a free-piston Stirling engine technology for cooling. The Thermo TSX was measured twice, as it offers two operating modes.
A study by Madsen & Høgdall estimates the energy savings to be approximately 32%.
That means changing the temperature by just 10 degrees saves you up to one-third of the energy!
This translates to $200–400 per freezer and can easily add up to five-figure savings for entire institutions.
But What If?
Commonly, there are two criticisms (or maybe myths) that you will encounter.
The first one we should address is that if freezers fail, you have far less time to protect your samples.
Here is data showing how long it takes for a freezer to increase in temperature when you unplug it:
Click to enlarge. I copied two data sets for you: one from the Office of Sustainability at the University of California, published in 2016, and one from Madsen and Høgdall from 2026, just to show how large the differences between models and measurement conditions can be. I also edited the graph on the right slightly and added the time in hours to make the already tedious comparison a bit easier. Also, keep in mind that freezers have, to some extent, an uneven temperature gradient inside and normally operate 3–5°C below the set point. Both publications investigate these measurements in more detail.
Please note that Madsen & Høgdall highlight the significant variation between freezers, and different case studies show different results.
However, you can generally estimate that it takes only one to three hours longer for a freezer at -80°C to reach room temperature.
Of course, the decision is up to you, but if it happens on a weekend, this extra time won't save your samples.
If you argue that your samples shouldn't reach -50°C and that having an additional hour to organize a new freezer is quite important, that is a valid argument.
But it also means that you will probably want to have some sort of monitoring system that alerts you when something is wrong. (And this should normally also kick in once your freezer is about to fail…)
Feelings vs Data
But, of course, we also have to address the second problem, which is the stability of your samples.
Many scientists claim that the stability of samples is lower at -70°C.
I am currently working on a more comprehensive literature review.
I will share all the literature on samples stored at -70°C vs -80°C I can find during our summit on October 28th.
However, I have heard of one single case where people allegedly had issues with spores at -70°C, but nobody could tell me exactly what the problem was…
And the literature does not support this point either.
Recently, I went through a paper by Ishiki et al. that compared methods to assess Alzheimer's biomarkers in blood.
At the top, you can see their workflow, and in the lower right panel, the results from storage are shown. The panel on the left shows the effects of freezing conditions - the plots and error bars indicate the mean values and standard deviations for 10 plasma samples. The y-axis shows recovery, calculated as the percentage of the Aβ40 or Aβ42 level obtained under each condition relative to the level obtained under the reference condition.
They found freezing at -80°C or in liquid nitrogen produced slightly better results, while all methods were within diagnostic allowable ranges.
However, storing the samples at -70°C produced results that were well within the variation seen in non-frozen samples after two weeks.
Applying the Knowledge
Nobody knows why we store our samples at -80°C.
Some argue that it was simply a marketing strategy by manufacturers to give them a claim as to why their freezers were superior.
There are several reports you can find from all over the world where labs change their freezer temperature. Moreover, in the Freezer Challenge 2025, more than 3000 labs participated with about 37 000 freezing units. In other words, there is a lot of evidence that change is possible.
Others mention that once the technology was advanced enough to actually reach these low temperatures, -80°C was the natural next step.
When I talk to my contacts, nobody remembers with certainty how things were a few decades ago.
In the end, there is no physical, chemical, or biological necessity behind -80°C that wouldn't apply for any other low temperature.
Therefore, if your colleagues are concerned, you now have a few studies that support -70°C.
And yes, I will share more studies, as well as some additional tricks for how you can save energy with your freezers, at the summit.
How We Feel Today
I guess that applies to -80 as much as it does to smoking However, Hollywood seems to have bettered itself already...
References
Madsen, C. L. et al., 2026. ULT freezer performance and dual-temperature storage in a modern biobank: preserving sample integrity during transition. Journal of Laboratory Medicine, 50(1), 10–20. doi:10.1515/labmed-2025-0108.
Ishiki, K. et al., 2024. The appropriate sample-handling procedure for measuring the plasma β-amyloid level using a fully automated immunoassay. Scientific Reports, 14, 14266. doi:10.1038/s41598-024-65264-1.
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