Site Overlay

Heat Detectors

How protected are you and your family against any fire outbreak in your home? Once you can answer this question, you’d put all the necessary preventive measures against getting harmed from a fire outbreak. In this review, we would be showing one of the preventive measures you can put in place to avoid getting harmed from a fire, which is a heat detector.

All you need to know about heat detectors are in this guide, endeavor to read through, your family’s safety might depend on it someday.

What is a Heat Detector?

Heat detectors detect the presence of heat and an increase in air temperature. These detectors have few false alarms but, they take longer to identify a fire than a smoke detector. They’re ideal in situations where smoke detectors may cause false alarms such as steamy, humid, or dusty environments. Infrequently occupied areas like storage facilities, warehouses, or machine rooms also use these types of detectors.

All heat detectors have this thermal lag. Heat detectors have two main classifications of operation, “rate-of-rise” and “fixed temperature”. The heat detector is used to help in the reduction of property damage.

  • Fixed temperature heat detectors

This is the most common type of heat detector. Fixed temperature detectors operate when the heat-sensitive eutectic alloy reaches the eutectic point changing state from a solid to a liquid.

Thermal lag delays the accumulation of heat at the sensitive element so that a fixed-temperature device will reach its operating temperature sometime after the surrounding air temperature exceeds that temperature. The most common fixed temperature point for electrically connected heat detectors is 58°C (136.4°F).

  • Rate-of-rise heat detectors

Rate-of-Rise (ROR) heat detectors operate on a rapid rise in element temperature of 6.7° to 8.3°C (12° to 15°F) increase per minute, irrespective of the starting temperature. This type of heat detector can operate at a lower temperature fire condition than would be possible if the threshold were fixed. It has two heat-sensitive thermocouples or thermistors.

One thermocouple monitors heat transferred by convection or radiation while the other response to ambient temperature. The detector responds when the first sensing element’s temperature increases relative to the other.

Rate of rise detectors may not respond to low energy release rates of slowly developing fires. To detect slowly developing fires combination detectors add a fixed temperature element that will ultimately respond when the fixed temperature element reaches the design threshold.

Both the rate-of-rise detectors and the fixed temperature detectors are great for sensing fires. However, heat detectors have drawbacks. Although they are great at heat detection, they won’t be able to detect a smoldering fire quickly. They are best for detecting high-heat fires.


Heat detectors commonly have a label on them that reads “Not a life safety device”. That is because heat detectors are not meant to replace smoke detectors in the bedrooms or the hallway outside of the bedrooms.

A heat detector will nonetheless notify of a fire in a kitchen or utility area, e.g., laundry room, garage, or attic, where smoke detectors should not be installed as dust or other particles would affect the smoke detector and cause false alarms. This will allow extra time to evacuate the building or to put out the fire, if possible.

Mechanical heat detectors are independent fire warning stations that — unlike smoke detectors — can be installed in any area of a home.

Portability, ease of installation, and excellent performance and reliability make this a good choice for residential fire protection when combined with the required smoke detectors. Because the detectors are not interconnected, heat activation identifies the location of the fire, facilitating evacuation from the home.

Each type of heat detector has its advantages, and it cannot be said that one type of heat detector should always be used instead of another. If one were to place a rate-of-rise heat detector above a large, closed oven, then every time the door is opened a nuisance alarm could be generated due to the sudden heat transient.

In this circumstance, the fixed threshold detector would probably be best. If a room filled with highly combustible materials is protected with a fixed heat detector, then a fast-flaming fire could exceed the alarm threshold due to thermal lag. In that case, the rate-of-rise heat detector may be preferred.

The three most common smoke detectors are ionization, photoelectric, and combination ionization/photoelectric. All smoke detectors sound an alarm, when they identify smoke, to notify a building’s occupants. What differentiates these detectors from one another is the way that they detect smoke.

How does a heat detector work?

There are two types of heat detectors, as we have seen above,  although they operate differently, essentially provide the same outcome.

Electro-pneumatic heat detectors contain a diaphragm that 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 center 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 meters squared but it is possible to link up to 20 heat detectors in any given circuit, providing a range of up to 100 meters. 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 center of the room as possible to ensure that the entire vicinity is covered. Also, choose a spot that is at least 10cm from a wall or corner.

Types of Fires for Heat Detection

  • Low-Energy Fire

There are two main types of fire: low-energy fires and high-heat fires. A low-energy fire smolders; it consumes fuel slowly and gives off a lot of smoke. However, this type of fire emits very little heat. Because this fire gives off more smoke than heat, thermal detection may fall short and take too long to detect this fire. By the time the heat sensor is activated, the fire will have caused severe damage to the home.

  • High-Heat Fire

The second type of fire is a high-heat fire. A high-heat fire consumes fuel quickly. As the fire eats, the flames grow higher and higher. These types of fires can be caused by an explosion or combustion. These fires feed off of easy-to-burn material such as paper, hay, or dry wood. This fire will trigger a heat detector fairly quickly. Heat Detectors are optimal for sensing this type of fire.

As a general rule, the only time to use a standalone heat sensor is if you are afraid that using a smoke detector may result in false alarms. Smoke detectors will usually respond to a fire more quickly than a heat detector. That is why they are recommended in most cases. But there are some times when it is better to use a heat sensor.

Some areas of the home feature excessive dust or moisture that could cause a smoke detector to think there is a fire in the building when really there isn’t. This can also occur in areas where smoke may be periodically present, including kitchens where food is being cooked and designated areas for smoking tobacco or other herbs. In these areas, it may be better to use a standalone heat detector.

Some of the most popular locations to use standalone heat detectors instead of smoke detectors include bathrooms, attics, garages, kitchens, and designated smoking areas. Using a smoke detector in any of these areas could result in a false alarm due to excessive dust, moisture, or smoke in the room. By using heat detectors, you can still monitor these areas for a fire, without having to worry about a false alarm.

Remember that false alarms can still occur with a heat sensor if it is mounted in a poor location. A heat sensor should be placed away from any vents or air ducts that may cause interference. The sensor should have its vents easily accessible, and it should not be blocked by other objects or obstacles.

It is recommended that the device be placed high up off the ground or ceiling. Keep in mind that heat rises, and you will want to give the sensor the best chance of detecting unusually high temperatures.


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.