Temperature Mapping Study: A Step-by-Step Guide

What Is a Temperature Mapping Study?

A temperature mapping study is a documented test in which multiple calibrated data loggers record temperature, and often humidity, at many points across a storage space at the same time. The combined data shows how conditions vary in three dimensions and over time.

Mapping answers three questions:

1. Does every part of the space stay within the required range?
2. Where are the warmest and coldest points?
3. Where should permanent monitoring sensors be placed?

It's usually part of the qualification of a storage area or equipment, typically in operational qualification (OQ) for an empty space and performance qualification (PQ) for a loaded space.

Why Temperature Mapping Is Required

Temperature-sensitive products must be stored within their labelled conditions everywhere they sit, not just near a thermostat. In most storage spaces, temperature isn't uniform: air near doors, external walls, lights, cooling units and the top of racks behaves differently from the centre.

Mapping is expected under GMP and GDP guidance, including WHO's technical guidance on temperature mapping of storage areas. Regulators and auditors typically ask for mapping reports for warehouses, cold rooms, freezers and refrigerators used for medicines, vaccines and biologics.

Without mapping, you can't show that products stored in corners, high racks or near doors were safe, and you can't justify where your monitoring sensors are.

When Should You Do a Mapping Study?

• Before first use of a new storage area or piece of equipment.
• After significant changes: new racking or layout, HVAC or cooling changes, major repairs, or change of use.
• Seasonally, for spaces affected by outside conditions, especially warehouses (usually summer and winter).
• Empty and loaded, since stock changes airflow.
• Periodically, as defined in your quality system, commonly every one to three years, or after a trend of excursions.

Step 1: Write the Mapping Protocol

Never start a mapping study without an approved protocol. It defines what you'll do and how you'll judge the result, before you see any data.

A mapping protocol usually includes:

• Objective and scope: which space, which conditions (empty, loaded, summer, winter).
• Description of the space: dimensions, layout drawing, racking, doors, cooling and HVAC units, existing sensors.
• Acceptance criteria: the required range (for example 2–8°C or 15–25°C), and how excursions will be judged.
• Equipment: number and type of loggers, accuracy, calibration status and certificate references.
• Logger positions: a numbered placement plan with a drawing.
• Logging interval and duration: for example every 1–5 minutes for 7 days.
• Test conditions: door-opening tests, power-failure or recovery tests, if included.
• Data analysis method: how you'll find hot and cold spots, calculate statistics and MKT if needed.
• Responsibilities and approvals: who executes, reviews and approves.
• Deviation handling: what happens if a logger fails or something unexpected occurs.

Step 2: Choose and Prepare the Data Loggers

The quality of your mapping depends on the loggers. Check that they:

• Are accurate enough: commonly ±0.2°C to ±0.5°C, depending on the range required. Tight ranges need better accuracy.
• Have valid calibration: traceable certificates, ideally from an NABL or ISO 17025 accredited lab, covering your temperature range.
• Cover the range: for freezers and ultra-low freezers, use probe loggers rated for the temperature.
• Measure humidity if the space has humidity limits.
• Are time-synchronised: all loggers set from the same computer clock, with the same start time and interval.
• Have enough memory and battery for the full study at your interval.

Label every logger with its position number, and record each serial number against its position.

See: temperature mapping data loggers · probe data loggers for freezers

Step 3: Plan Logger Placement

Placement is the most important part of the study. Combine a 3D grid with risk-based positions.

The 3D grid

Divide the space into a grid across its length and width, and place loggers at several heights at each grid point, typically low, middle and high. For tall racking, add more heights.

Risk-based positions

Add loggers wherever conditions are likely to differ:

• Near doors and loading docks
• Near cooling units, evaporators and air outlets
• Near external walls, windows and roof
• Near lights and other heat sources
• In corners and dead air zones
• Next to existing monitoring sensors (to compare readings)

Typical number of loggers

These are practical ranges. Your protocol should justify the final number based on the size, layout and risk of the space. In warehouses, grid spacing of a few metres is common, with closer spacing near risk areas.

Placement tips

• Don't place loggers directly against walls, cooling coils or in direct airflow unless that's what you're testing.
• Keep the logger in the space where product is stored, at product height.
• For loaded studies, place loggers among the product, not on top of cartons.
• Photograph every logger in position for the report.

Step 4: Run the Study

• Duration: long enough to capture normal daily and weekly cycles, including weekends, commonly around 7 days. Equipment like fridges may be shorter, around 24–72 hours, if justified in the protocol.
• Logging interval: commonly 1 to 5 minutes, so short spikes aren't missed.
• Operate normally: for performance mapping, the space should run as it does every day, including deliveries, door openings and defrost cycles.
• Record events: keep a log of door openings, deliveries, defrosts, power cuts and anything unusual, with times. This explains spikes later.

Optional challenge tests

Many studies add:

• Door-opening test: open the door for a set time and record how fast the temperature recovers.
• Power-failure test: switch off power and record how long the space stays within range, then how fast it recovers. This shows how much time you have to respond to an alarm.

Step 5: Analyse the Data

After the study, download every logger and combine the data. For each position, calculate:

• Minimum, maximum and average temperature
• Time outside the acceptance range, if any
• Mean kinetic temperature (MKT), where your protocol or quality system requires it

Then for the whole space:

• Identify the hot spot and cold spot: the positions with the highest and lowest readings, and when they occurred.
• Check uniformity: the spread between the warmest and coldest positions.
• Review events: match spikes with door openings, defrosts or other logged events.
• Assess challenge tests: recovery times after door opening and power failure.

A temperature-over-time chart for all positions, plus a colour-coded layout drawing (a "heat map") showing average or maximum readings at each position, makes results easy to understand.

Step 6: Write the Mapping Report

A mapping report normally includes:

• Summary and conclusion: pass or fail against the acceptance criteria
• Reference to the approved protocol
• Description of the space and test conditions
• Logger list with serial numbers, positions and calibration references
• Placement drawing and photos
• Results tables per position and charts
• Hot spot and cold spot identification
• Challenge test results
• Deviations and their impact
• Recommendations: permanent sensor positions, unusable zones, corrective actions
• Review and approval signatures

Step 7: Act on the Results

• Place permanent monitoring sensors at the hot and cold spots, and at points representative of the stored product.
• Mark no-storage zones where conditions fall outside the range, for example directly in front of a cooling unit or near a dock door.
• Fix problems, such as poor airflow, gaps in insulation or faulty door seals, and re-map if needed.
• Set alarm limits and delays based on recovery times from the challenge tests.

Continuous monitoring then watches the critical points found during mapping. See wireless temperature data loggers and multi-point monitoring systems.

Mapping Different Spaces

Warehouses

Large, tall spaces with the biggest variation. Map in summer and winter, include high racking positions, and pay extra attention to roofs, external walls, dock doors and HVAC outlets. Humidity mapping is often required too. See temperature and humidity data loggers.

Cold rooms

Watch the evaporator area, door and corners. Include defrost cycles in the study, and run door-opening and power-failure tests to set alarm delays.

Refrigerators and freezers

Map each shelf level, including near the door and the back wall. For freezers at -20°C or -80°C, use probe loggers so the electronics aren't inside the freezer.

Reefer vehicles and containers

Map the cargo space front, middle and rear, at floor, middle and top, near the doors and the refrigeration unit, during a representative journey or a static test.

Common Temperature Mapping Mistakes

• Too few loggers, or placing them only where it's convenient.
• Missing risk points like doors, cooling units and high racks.
• Loggers not time-synchronised, making position-to-position comparison unreliable.
• Expired or missing calibration certificates.
• Studies that are too short to capture weekends, defrosts or normal operations.
• Mapping only once, without seasonal or post-change studies.
• Not acting on the results: no permanent sensors at hot or cold spots.

Temperature Mapping Checklist

Download checklist (PDF)

Frequently Asked Questions