Temperature mapping (also called thermal mapping or temperature qualification) is the structured process of measuring how temperature is distributed across a storage space, cold room or vehicle over time. Its purpose is to find the hot spots, cold spots and gradients that a single wall thermometer will never reveal — and to prove, with documented evidence, that the space holds product within its required range.
Mapping is the foundation that permanent monitoring is built on: it tells you where to place your fixed sensors so they sit at the genuine worst-case locations. Under EU GDP (2013/C 343/01), an initial mapping exercise is an explicit expectation before a storage area is first used, repeated on a risk basis and after significant changes. This guide walks through the whole exercise — when it's needed, how to size and place sensors, how long to run, and what the report must contain to satisfy an inspector.
Mapping vs. monitoring: what's the difference?
These two terms are constantly confused, and the distinction matters for both compliance and budget. Mapping is a point-in-time study that characterises a space; monitoring is the permanent, continuous measurement that runs forever afterwards.
Think of it this way: mapping answers "where do I need to watch?" and monitoring answers "is it still in range right now?". You qualify a space once (and re-qualify periodically), then monitor it continuously at the worst-case points the map revealed. One does not replace the other.
When is temperature mapping required?
Mapping is expected at several points in an asset's life, and skipping it is one of the most common audit findings in regulated storage. The trigger is usually a change that could alter how heat moves through the space.
- Before first use of a new warehouse, cold room, freezer or refrigerated vehicle.
- After significant changes — HVAC modification, racking re-layout, relocation, new doors, or a change in stored volume or product mix.
- Seasonally, where ambient conditions materially affect the space: a summer study and a winter study, because the worst-case locations can move between seasons.
- On a periodic, risk-based cycle defined by your quality system — commonly annually for GDP/GMP storage.
- After a major excursion or equipment failure, as part of the investigation and CAPA.
How many sensors do you need?
There is no single number — the count scales with the volume and complexity of the space. WHO and EU GMP guidance is to use enough sensors to characterise the full three-dimensional space, including the likely extremes near doors, heat sources, HVAC supply and return points, and at different heights (floor, mid, ceiling).
As a rough starting point, small pharmaceutical cold rooms are often mapped with 9–15 sensor positions; a large ambient warehouse can need 30, 50 or many more, distributed on a grid and at multiple heights. The mapping protocol should justify the number and placement of sensors against the geometry of the space rather than picking a round number.
Every mapping sensor must carry a valid, traceable calibration certificate for the study to be defensible — an out-of-calibration logger invalidates the data it produced.
How long should a mapping study run?
A study must run long enough to capture normal operating patterns and at least one full cycle of any equipment, such as a defrost cycle. For warehouses, 48–72 hours under representative conditions is typical; small controlled chambers may need less, while large ambient spaces with slow thermal mass may need longer.
Run the study under realistic conditions — normal door openings, normal stock levels and normal traffic — not on a quiet weekend that flatters the result. Where your risk assessment calls for it, add deliberate challenge tests such as a simulated power loss, an extended door-open event, or a full-load scenario, and document them separately.
Open-door and power-loss challenge tests
Beyond steady-state distribution, regulators increasingly expect evidence of how a space recovers from a disturbance. Two challenge tests are common: an open-door test (how fast does the zone warm, and how long to recover to range?) and a power-loss/recovery test (what is the temperature trajectory if cooling stops?).
These tests define realistic alarm delay settings for the permanent monitoring system that follows — long enough to ignore a normal door opening, short enough to catch a genuine failure. Mapping and alarm design are therefore two halves of the same exercise.
What a compliant mapping report must contain
The deliverable is as important as the measurement. A report that an auditor will accept ties the raw data back to a documented, repeatable method — not just a graph.
- The mapping protocol: objective, acceptance criteria, sensor grid and placement rationale.
- Calibration certificates for every sensor used, traceable to national standards.
- Raw time-temperature data and summary statistics (min/max/mean, and MKT where relevant).
- Identification of hot spots, cold spots, gradients and any out-of-specification locations.
- Results of any open-door or power-loss challenge tests.
- Recommended permanent monitoring sensor positions at the worst-case locations.
- A signed qualification summary, conclusion and any deviations encountered during the study.
From mapping to permanent monitoring
Mapping is a point-in-time study; it does not replace continuous monitoring. The whole point of the exercise is to place permanent sensors where they will catch problems first. Once the worst-case positions are known, fixed wireless sensors are installed there to provide ongoing, audit-ready evidence between mapping cycles, logging continuously (Seemoto's default is a 5-minute interval, configurable to 1 minute) with real-time alerts.
Seemoto offers temperature mapping as a professional service and supplies the continuous monitoring that follows it, so the placement recommendations flow directly into a live system rather than sitting in a PDF on a shelf.
Key takeaways
- Mapping qualifies a space (point-in-time); monitoring maintains control (continuous). You need both.
- Map before first use, after significant changes, seasonally where ambient varies, and after a major failure.
- Sensor count scales with volume and geometry — ~9–15 for a small pharma cold room, far more for ambient warehouses; every sensor must be calibrated.
- Run 48–72 hours under realistic conditions for warehouses, and add door-open/power-loss challenge tests where risk warrants.
- A compliant report ties raw data to a documented protocol, calibration records, hot/cold-spot analysis and placement recommendations.