NFPA 72 Chapter 5 Initiating Devices — Heat Detectors

This is a continuation on the series of articles about the most important requirements in NFPA 72 National Fire alarm Code Book. Make sure to read the first article NICET Study Guide — NFPA 72 Chapter 4 Fundamentals of Fire Alarm. In this articles I will discus Heat Detectors and give you the most important code requirement that you must know about for the exam.

General Requirements for all types of initiating devices:

· Initiating devices shall only be installed in accessible locations.

· Initiating devices shall be protected if they are exposed to mechanical damage.

· A mechanical guard shall be listed for use with the detector.

· Initiating devices shall be supported by another means besides their own conductors.

· Initiating devices shall be installed in a manner to allow for regular maintenance.

· Duplicate terminals shall be provided on the detectors for monitoring the wires for integrity.

· Heat & Smoke Detectors Shall not be recces mounted unless they are listed and tested.

· In a non required application where detectors are installed to achieve specific fire safety objective, additional detectors shall not be required throughout.

Location of Heat Detectors

· Ceiling mounted heat detector shall be located not less than 4 inch from side wall

· Sidewall mounted heat detector shall be located between 4 and 12 inches from the ceiling.

· Line type heat detector shall be mounted within 20 feet from the ceiling.

· In a solid joist construction heat detectors shall be mounted at the bottom of the joist.

· In beam construction detectors can be mounted on the bottom of the beam if the beams are less than 12 inches deep and less than 8 inches on center.

Spacing of Heat Detectors

Smooth Ceiling

· Any point on the ceiling shall have a detector within 0.7 times the listed spacing.

· Distance from a detector to a wall shall not exceed 1/2 of the listed spacing.

· Heat Detectors Shall not Exceed their listed spacing.

· In irregular areas spacing of heat detector is permitted to be more than listed spacing, provided that it should be within 0.7 time the listed spacing from a wall.

Beam Construction

· The ceiling shall be treated as a smooth ceiling if the beam is less than 4″

· When beam is more than 4″ spacing shall be no more than 2/3 of smooth ceiling spacing.

· When beam project more than 18 inches from ceiling and more than 8 feet on center. than these pockets shall be treated as a separate areas.

Sloped ceiling

· The first row of detector in sloped ceiling shall be within 3 ft of the peak.

· If the slope is less than 30 degrees, detectors shall be spaced using the height at the peak.

· If the slope is more than 30 degree, then the average slope height shall be used except the first detectors on the peak.

High Ceiling

· On ceiling between 10 feet and 30 feet high, the spacing shall be reduced according to table below.

· The minimum spacing shall not be less than 40% the height of the ceiling

Do visit:

This post should be part of your study guide for NICET Level 1 and Level 2. Please pay attention to the two tables above, they are table and on pages 72–39 and 72–40 respectively, make sure to label these sections. I am sure that these tables are good candidate for questions on the exam. I will discuss the requirement of smoke detectors and other initiating devices in upcoming post. as always please let me know in the comment area below on what you think about this post and what would you like to see in future articles.


  • Types of initiating devices include:
  • Manual fire alarm boxes / Manual Pull Station / Manual Call Point
  • Smoke detectors
  • Heat detectors
  • Flame detectors
  • Sprinkler waterflow detectors
  • Switches indicating actuation of fire suppression systems
  • Valve supervisory devices
  • Pressure supervisory devices
  • Level supervisory devices