How Heat Detectors Work ?

heat-detector-1A heat alarm is designed to detect heat instead of smoke, the alarm contains a thermistor which is set to respond to temperatures above 58°C.
heat-detector-2When a fire breaks out hot air from the fire will rise and enter the sensor chamber.
heat-detector-3When temperature inside the chamber reaches 58°C a signal is sent to the integrated circuit which causes the alarm to sound alerting the occupants to the fireHeat Detectors are normally used in environments where a smoke detector might generate false alarms. Heat detectors can be situated in the kitchen and the garage, because heat alarms don’t react to smoke they are not prone to false alarms from cooking and exhaust fumes.Rate of Rise heat detectors will alarm if the temperature rises very quickly, or if the temperature reaches a set threshold. This type of detector would be the first choice in an environment where a smoke detector could not be used.

In some environments, such as boiler rooms, fast rates of rise of temperature can be expected normally, meaning that there would be a risk of false alarm when using a rat-of-rise device. In this case a fixed temperature detectors give an alarm once the temperature has reached a preset threshold, most commonly 58°C or 78°C for EN54-5 Class AS or BS respectively.


When mounted on a flat ceiling, heat detection devices have an individual coverage of 5.3m radius. However these radii must overlap to ensure there are no “blind spots”. Therefore individual coverage can be represented by a square measuring 7.5 X 7.5m giving an actual coverage area of 56.3m² per device.