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What is a Heat Detector?

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- Published 17th August 2018

Put simply, a heat detector - or heat alarm - is a device that's used to detect any substantial increase in temperature which may indicate a fire is about to break out.

If there is a fire in the vicinity of the alarm, the convected thermal energy from the flame raises the temperature of a heat-sensitive element in the heat detector. Once this occurs, the element triggers an alarm which then sounds, alerting anyone within ear-shot of the device.

How does a heat detector work?

There are two types of heat detectors which, although they operate differently, essentially provide the same outcome.

Electro-pneumatic heat detectors contain a diaphragm which moves when there is a change in pressure owing to a shift in the ambient temperature. When the diaphragm moves, an electric circuit is completed, which activates the alarm.

Rate of Rise – or ROR – heat detectors operate using two heat-sensitive thermocouples. One of the thermocouples monitors the heat transferred by convection or radiation while the other measures the background temperature of the room. An alarm sounds when there’s a disparity between the two, suggesting that a fire is about to break out.

Heat detector locations

Your heat detector location is vital for the safeguarding of your building. Although it’s better to install a heat detector on the centre of your room’s ceiling, you can position it on a wall, 50cm or so below the ceiling height.

Heat detectors are perfect to use where a smoke alarm isn’t suitable – for instance, in rooms where there are high levels of smoke, fumes and dust, like garages or lofts. It’s also a good idea to use a heat detector in areas where chemicals or highly flammable substances are stored.

Heat detector circuit

Each heat detector covers an area of 5 metres squared but it is possible to link up to 20 heat detectors in any given circuit, providing a range of up to 100 metres. The benefit of this, of course, is that you can protect your whole building within one heat detector circuit. If a fire breaks out in the basement, you’ll be alerted by your nearest heat detector, even if you’re on the very top floor of the building.

Sentinel’s heat detectors are ideally suited for use in a circuit since they are completely wire-free, so can be installed with a minimum of fuss and mess.

Heat detector spacing

It’s important to think about the spacing of heat detectors ahead of time. Position your heat alarm as close to the centre of the room as possible to ensure that the entire vicinity is covered. Also, choose a spot which is at least 10cm from a wall or corner.

Should you use a smoke detector too?

Since heat and smoke alarms operate in different ways – each detecting increases in heat and smoke, respectively – it’s better to use a combination of the two to ensure your building is completely protected.


You can find out the differences between a smoke and heat detector here.