-70 is the new -80

https://www.mygreenlab.org/-70-is-the-new--80.html

The idea
Chilling up your ultra-low temperature (ULT) freezer from -80C to -70C has two major benefits:  it can reduce energy consumption by 30-40%, and in doing so it can prolong the life of your freezer.  This means less downtime and less chance that your samples will be compromised.

But is it safe to store my samples at -70?
In the majority of cases, the answer is a resounding YES.  Nucleic acids can be safely stored at -20C, or -70C, depending on how long they need to be stored, and most proteins can be safely stored at -70C.  Bacteria and viruses are also generally safe at -70C.  In fact, fifteen years ago all ultra-low freezers were set to -65C or -70C.  

Evidence that -70C is a Safe Temperature to Store Samples

Storing microorganisms

Storing protein

Publications

Storing DNA at -20C

Study comparing DNA stored at -20C and -80C

Has anyone else tried this?
YES.  CU-Boulder, UC Davis, Harvard, Dartmouth, and UC Santa Barbara were among the first in the United States to adjust their ULT freezer set points. Now, thanks to the great work of Freezer Challenge participants, labs in universities and companies around the world have chilled up. 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 -70C.  Some labs have offered to include their information on a list of samples successfully stored at -70C.  That list can be found here.