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 in 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.