Chilling Up Your ULT Freezer

Learn more about the benefits of chilling up your ULT freezer and check out the spreadsheet with successfully stored samples at -70C across the United States!

We want to help you be confident in chilling up your ULT freezer!

It is understandable to be hesitant to change the temperature of your ULT freezer that might contain your life’s work and proudest accomplishments that cost you an immense amount of time and money. The Pitt Sustainability Team wants to provide you with the best information we have about chilling up ULT freezers so that you can confidently chill up yours and get one step closer to becoming a Pitt Green Lab!

Did you know?

According to the U.S. Department of Energy, conventional ultra-low temperature (ULT) freezers can use as much energy as an average household every day, which is about 20 kWh.


Benefits of chilling up

Also according the the U.S. Department of Energy, the simple and safe adjustment of chilling up your ultra-low temperature (ULT) freezer from -80°C to -70°C has two major benefits: it can reduce energy consumption by 30%, and in doing so it can prolong the life of your freezer.  This means less down time, and less chance that your samples will be compromised.

Is it safe to store samples at -70°C?

According to extensive research done by the non-profit organization My Green Lab, in the majority of cases the answer is a resounding YES.  Nucleic acids can be safely stored at -20°C, or -70°C, depending on how long they need to be stored, and most proteins can be safely stored at -70°C.  Bacteria and viruses are also generally safe at -70°C. The CDC Recommended Temperatures for Storing Vaccines for freezers are between -50°C and -15°C and for refrigerators are between 2°C and 8°C (average 5°C).

Furthermore, ULT freezers used to only be manufactured to reach -70°C. It is suspected that the switch from -70°C to -80°C was a result of marketing by manufacturers to sell ULT freezers because there is no demonstrated scientific need for -80°C for samples stored in ULT freezers.

Has anyone else tried this?

According to My Green Lab, CU-Boulder, UC Davis, Harvard, Dartmouth, and UC Santa Barabara were among the first in the United States to adjust their ULT freezer set points. AstraZeneca, Charles River Labs, Genentech, the CDC, Imperial College London and NUI Galway are just a few of the hundreds of places where at least some, if not all, ULT freezers are now set to -70°C.

At the International Institute for Sustainable Laboratories (I2SL) conference in September 2013, a presentation by the CDC included the fact that they raised 60 of the ULT freezers to -70°C from -80°C on one of their campuses. You can read more here.

Some labs have offered to include their information on a list of samples successfully stored at -70°C at the link below. The sheet automatically updates every five minutes. Please note that this database is not science-based data on appropriate temperatures for samples, though these temperatures have been successful for various labs for years.

***Biological Samples Stored Long Term at -70C or Warmer Spreadsheet***


PEER REVIEWED STUDIES proving -70°C or warmer storage

Storing microorganisms – “Since 1994, 6,198 yeasts and 391 molds belonging to 25 and 37 species, respectively, were stored in Microbank cryogenic vials at >=130°C in liquid nitrogen and at -70°C in a freezer. All of the isolates, with the exception of 45 yeasts and 15 dermatophytes, were recovered from both storage temperatures. Good reproducibility was demonstrated for amphotericin B, fluconazole, and voriconazole MICs determined for random isolates.” (Source)

Storing protein – “It can be concluded that −70°C is the right temperature for storage to maintain the PON1 activity for at least one year. Storage at a lower temperature in liquid nitrogen (−196°C) is not necessary.” (Source)

Study comparing DNA stored at -20C and -80C – “Genomic DNA stored at -20°C and -80°C was of good quality, and these samples withstood multiple freeze-thaw cycles. For short term studies genomic DNA can be stored at 4°C or even RT without degradation, but samples should be monitored for DNA concentration and evaporation. DNA stored in dry state at room temperature showed degradation more rapidly then other storage conditions.” (Source)

Nucleic Acids at -20C – “At -20 degrees C, samples containing HIV-1 were followed up for approximately 3 years and the results obtained show no decay in HIV-1 RNA detectability. Regardless of the HIV-1 RNA concentration, samples stored at 5 degrees C maintain their titre for at least 14 days. At 25 degrees C, the HIV-1 RNA half-life was determined at nearly 7 days. The HBV DNA, at 5 degrees C and 25 degrees C, is stable for at least 28 days, regardless of the initial titre.” (Source)

Stability of Extracted RNA at various temperatures – “Extracted RNA stored at -20°C and -80°C was of good quality, and the RNA was stable for up to 10 freeze-thaw cycles. Extracted RNA can be stored at 4°C for 14 days without degradation. Evaporation may occur during this time. Extracted RNA can be stored safely at room temperature for 2 days without degradation.” (Source)

Stability of human serum – “Storage at – 20°C is sufficient to maintain a proper assay outcome of most of the total antioxidant assays, although storage at – 70/80°C is to be preferred for longer storage times.” (Source)

Upright ULF temperature variability – “Allowing for proper free airflow space within a unit decreases the temperature variation to which specimens are exposed during storage and enables the freezers to maintain specimen temperatures at or below -70C, thereby maintaining specimen integrity.” (Source)

Viral stability – “Bulk and dispensed plasma were stored at -20º C prior to 1997 and subsequently at -70ºC. Tests conducted for anti-HIV, anti-HCV and HBsAg over 11 to 20 years with the same or similar test methods to determine the long-term stability of these analytes in MPP indicated no detectable deterioration of these analytes, and no downward trend in reactivity.” (Source)

You can also check out information from UC-Boulder summarizing some of these and other publications.

When should I not chill up my freezer?

If your freezer is only partially full, you may not want to raise the set point to -70°C. This is because a  lower thermal mass causes higher temperature swings when the freezer is opened. If you do still choose to chill up your freezer, be sure to monitor your freezer temperature closely. Otherwise, if your freezer is not full, offer to share space with another laboratory so you (and others!) can safely get the benefits of chilling up your ULT freezer.

Additional Information