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Heat Detector vs Smoke Detector: What to use?

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- Published 7th September 2018

If you haven’t replaced your fire alarm system during the last 10 years, it might be time to do so. But where do your start? Judging by the range of fire detection devices which are now available to you, it’s easy to get lost.

Fortunately, help is at hand. We’ve put together a guide to the main differences between a heat detector and a smoke detector to help you decide which will work best in the different areas of your house.

What is a heat detector?

Sometimes referred to as heat alarms, heat detectors are perhaps lesser known than smoke alarms. They also operate in a completely different way – as its name suggests – detecting signs of excessive heat in their vicinity, rather than smoke or fumes.

How heat detectors work?

Using thermocouple and electro-pneumatic technologies, heat detectors will sound an alert when the temperature of the room they are in is raised above a certain temperature.

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.

Thermocouple – or Rate of Rise – heat detectors contain two thermocouples which are sensitive to heat. The first thermocouple monitors the heat transferred by radiation or convection, the second reacts to the ambient temperature of the room. The alarm sounds when the temperature of the first thermocouple is raised above the temperature of the second, indicating a fire.

Where to use a heat detector?

Tired of your smoke alarm being set off every time you burn the toast? A heat detector could provide a solution. Unlike a smoke detector, a heat alarm will not alert you to an insignificant temperature change – it’ll only trigger once there is a perceptible rise in heat.

A heat detector is usually used in rooms where there is excessive dust or fumes – for instance, a garage or cellar – which a smoke alarm can mistake for dust, soot or combustible elements in the atmosphere. It’s also used in rooms where highly-flammable chemicals are stored.

Find out more about our heat detectors


What is a smoke detector?

Smoke detectors – or smoke alarms – are more traditionally used in residential properties. Although they are prone to making more mistakes than heat detectors, they do provide an invaluable resource for detecting the first sign of combustion. In short, no home should be without one.

How smoke detectors work?

Smoke alarms rely on ionization and photoelectric technologies to activate an alarm once smoke is detected. Ionization smoke alarms contain a small amount of radioactive material between two electrically charged plates, which ionizes the air and causes a current to move between the plates. When smoke enters the chamber, it disrupts the current which triggers an alarm.

Photoelectric-type smoke alarms direct a light source into a sensing chamber at an angle away from the sensor. When smoke enters the chamber it causes light to be reflected onto the light sensor, activating the alarm.

Where to use a smoke detector?

Since smoke detectors are sensitive to even just a small amount of smoke, it’s better to avoid placing one in locations that are prone to fumes or where food is prepared.

Find out more about our smoke detectors

Heat detector vs smoke detector: what to bear in mind

It’s important to remember that heat detectors do not pick up signs of smoke, which is usually one of the first signs of a fire.

So, to ensure your building is safeguarded against both, it’s a good idea to use a heat alarm alongside a smoke alarm.

Sentinel heat detectors can be used in circuit of up to 20 units, covering up to 100 metres. This means, of course, that if your heat alarm detects a sudden jump in temperature in the cellar, you smoke alarm on the top floor will activate too.

For more information, take a look at Sentinel’s smoke alarms and heat detectors.