What is a heat detector?
A heat detector responds to a rise in temperature rather than to smoke. It is used where smoke detection would give constant false alarms — kitchens, garages and some plant areas.
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<img src="https://fireoptix.co.uk/glossary/heat-detector/diagram.svg" alt="heat detector — diagram from FireOptix" width="880" height="620" loading="lazy">
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<a href="https://fireoptix.co.uk/glossary/heat-detector">What is a heat detector?</a> — diagram by
<a href="https://fireoptix.co.uk">FireOptix</a>
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</figure>It is a deliberate trade of speed for reliability. A heat detector signals later than a smoke detector, and that is acceptable in a room where a smoke detector would be disabled within a fortnight.
Types differ in whether they respond at a fixed temperature or to a rate of rise, and the choice depends on how the room's temperature normally behaves. A rate-of-rise device above a cooker line is a design decision, not a default.
Because it responds later, a heat detector in a room on an escape route is generally the wrong answer — the protection there needs to come before the smoke does.
In practice
A kitchen fitted with heat detection and a corridor fitted with smoke.
This is the right arrangement, and the kitchen's detector will not respond to a smouldering fire in a bin.
Heat detection is chosen where smoke detection would be unreliable, and the trade-off is a slower response to some fire types.
The compensating measure is usually the detection in the space the kitchen opens onto, which is why that door matters so much.
What goes wrong in practice
- Used on escape routes where earlier warning is needed.
- Fitted near heat sources that produce normal temperature swings, causing the false alarms it was meant to avoid.
- Substituted for a smoke detector to solve a false alarm problem without reassessing the room.