Last Revised: July 02, 2024

Freezer maintenance is essential to preserving valuable research samples and prolonging the life of your freezer. Old, iced-over inefficient freezers not only use substantially more energy than newer maintained units, but they are also more likely to crash, leading to a loss of samples, reagents, and researcher time.

Information sourced from ThermoFisher Scientific Guide to ULT Freezer Care and Maintenance.

NIH ULT Freezer User Level Preventative Maintenance Video

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Maintaining Ultra Low Temperature (ULT) freezers

  • Give freezers plenty of room to breathe: Airflow is critical to freezer longevity and function!
    • Ensure 6 inches of clearance between walls and other freezers and 8” of overhead clearance.
    • Do not store cardboard boxes or any flammables on top of freezers
    • Do not install under HVAC ducts.
    • Install freezers in spaces with a reasonable temperature range (15C-32)
Regular Maintanance
  • Perform user-level maintenance every 6 months (see minute 1:20 in NIH video above)
    • wipe down outside of freezer with a soft cloth
    • Clean the filters and condenser coils regularly
    • remove ice from the gasket and doors with a soft cloth
    • Call a service technician for more complex issues


  • Keep your freezer doors free of ice and frost:
    • well maintained gaskets and doors insure product protection!
    • Healthy gaskets reduce ice build-up:
      • wiped down gaskets monthly (or as needed) with a soft cloth
      • inspected gaskets for tears, bends, or pulling away from the freezer door.
    • Schedule maintenance with the vendor as needed.
    • Freezer doors can be gently de-iced with an ice scraper
    • Never use a sharp object to remove ice from a gasket or door!


  • Organize
    • keep inventory organized to save space and reduce stress on the unit
    • items are found with more ease inside an organized unit, limiting how long the freezer door has to remain open
    • minimize door opening frequency
    • keep unit full to reduce air displacement
    • Consider switching to plastic colorful boxes which hold up longer in freezers and allow for rapid identification.


  • Loading Samples
    • pre-cool samples in cold-rooms or -20C units, depending on the sample's destination
    • load samples in batches and one shelf at a time to allow the UTL to reattain operating temperature between loading




Filter Maintanance
  • Cleaning filters and coils annually
    • Locate and clean your freezer air filter. These are located behind the vents on your freezer, which can be popped off or unscrewed to show a foam filter similar to those found in vacuum cleaners.
    • Inspect filters and condensers regularly for dirt and dust
    • Vacuum condenser units and filters carefully and as needed.
      • Contact your building’s Facilities manager to borrow a vacuum.
    • Wash filters with mild soap and water. Then let them air-dry before reinstalling.
    • See minute 1:57 of NIH video above for details


  • Defrost and review inventory annually or when heavy ice-buildup occurs:
    • See minute 3:24 of NIH video above for details on defrosting a freezer
    • REPLACE GASKETS: Check gaskets and purchase new ones if needed to install while freezer is thawed!
    • Schedule a backup freezer to borrow space in through your department or Building Administrator
    • Give lab members a deadline to review their boxes, update their inventories, and toss unneeded materials according to University Biohazardous Waste Guidelines.
    • Transfer racks to backup freezer
    • Unplug the freezer to be defrosted: 
      • Place absorbent materials (towels, disposable bench pads, etc) beneath the freezer to catch water.
      • Turn off the unit and open the door
      • Let ice melt completely
        • Bulk ice can be removed occasionally using scrapers, but use caution and do not use force or sharp objects, which may puncture refrigerant piping and lead to harsh chemical exposure.
        • Remember to wear proper PPE (lab coat, safety glasses, cryogloves, etc) to protect yourself from freezer burn and any lost samples that have been trapped in ice.
      • When the freezer has come to room temperature (typically 24 hours), you may clean interior with a mild detergent and warm water.
      • Wait until the freezer is dry before plugging it back in. It will take about 12 hours for your freezer to pull down to its regular operating temperature after which racks may be transferred back to the freezer.
Maintaining a Freezer Inventory

An inventory for all freezers and refrigerators must be maintained by every laboratory. In addition to improving research efficiency and reducing unnecessary purchases of reagents, inventories provide biosecurity of valuable research reagents and samples. These may be as simple as a shared Excel spreadsheet or physical binder with printed templates or as sophisticated as online laboratory information management systems (LIMS).

To create an inventory:

  • Choose an inventory system. This Nature article highlights several software platforms, many of which are free or low-cost to academic labs.
  • Dispose of all old, unwanted, unnecessary and unlabeled materials according to University Biohazardous Waste Guidelines.
    • Use caution when discarding sealed tubes with frozen contents. The thawing process may cause the tubes to rupture. A labcoat, gloves, and eyewear protection should be used during freezer cleanouts. Tubes should be placed immediately into a biohazard bag and directly into the infectious waste stream without autoclaving.
    • For larger freezer cleanouts, coordinate with your Facilities manager to obtain large infectious waste bins that can be disposed of at a central building location. Do not allow large quantities of thawing biohazardous materials to accumulate in autoclave rooms.
    • Bag and seal all waste prior to disposing
    • For regulated materials (eg DEA regulated drugs, Select Agents, Risk Group 3 microorganisms, etc), follow inactivation and disposal protocols specific to those materials. Please reach out to a Biosafety Officer prior to disposing of these items!
  • Organize and clearly label all freezer and refrigerator contents.
  • Label freezers with an identifier and contact information in the event of an alarm or freezer malfunction.

Have an inventory software system you’d like to recommend? Have questions about how to safely defrost your freezers? Please reach out at

Penn Freezer Challenge

Penn Sustainability Green Labs sponsors an annual Freezer Challenge

Help improve the energy efficiency of research freezers across campus through good freezer maintenance. Participants have access to training, vendor demos, and more resources, while competing for prizes!

2024 Information:

The Penn Labs Freezer Challenge is in participation with the International Freezer Challenge that runs from January 1-July 31, 2024. Labs at Penn can register any time until June 30, 2024.