NICET Study Guide – 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.

Heat Detectors General Requirement

  • Heat detectors shall be classified by the temperature of operation and marked with a color code according to the following table
Temperature ClassificationTemperature RatingMax Ceiling TempColor Code
Low100-134 F80 FUnclolored
Ordinary135-174 F115 FUncolored
Intermediate175-249 F155 FWhite
High250-324 F230 FBlue
Extra High325-399 F305 FRed
Very Extra High400-499 F380 FGreen
Ultra High500-575 F480 FOrange
  • Heat detectors shall be marked with the listed operating temperature.
  • Spot type heat detector shall also be marked with the response time index.
  • Combination heat smoke detector shall be listed for no less than 50ft spacing.Heat Detector Mounting

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
Ceiling Height Above (Feet)Up to and Including (Feet)Multiply Listed Spacing By

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 (watch the video on how to use NFPA72 Book). 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.






Comments on this entry are closed.

  • Thank You for your site and practical ways to get started for studying and preparing. I am trying for my level 3 fire alarm and need as much help as I can get.

  • John,
    Your video’s and study guides are great! Keep up the good work. Many technicians have no idea what they are stepping into. The one thing that they are sure of is that they haven’t taken a test (other than their driver license renewal test) since their days in college and it’s intimidating for them.
    Best Regards,

  • So I am a little confused about the the smooth ceiling spacing and it being .7 times the the listed spacing…if I could give you an example and maybe you could walk me through it.. That would really help…ex-An octagonal room with a smooth ceiling measures 60 ft. wide, 60 ft long, and each side of the octagon measures 25 ft..How many heat detectors are needed?

    • Jason,
      the 0.7 rule basically states that any point on the ceiling should be within 0.7 times the listed spacing of a detector. if we take a typical 30×30 listed spacing, that means any point on the smooth ceiling should be within 21ft of a detector. so in your example start drawing circles with a radius of 21ft and put the detector in the center of the circle make sure that your circles cover the entire octagon. I would say 4 detectors should cover the area. also bear in mind that this is for ceilings 10ft and lower. if ceiling is greater than 10 feet, than you have to adjust the spacing.

  • Great site! there’s a wealth of information on here. But I have a question, if you don’t mind answering, did you ever go through the certification process with NICET, or did you just take the exam?

    • Thanks tucker for stopping by, I got my Level I certificate and working towards level II and Level III at this moment. I will document my journey in this site.

  • can we install these detectors by hanging them on a pipe of length 75cm from the roof level?

  • You’ve got a great site here, thank you for all your diligent work! I’m testing for my Nicet II in August (likely thanks to having stumbled upon your page whilst mindlessly pouring over my code books preparing for I), and have used several of your posts as launching points for my training program with apprentices. Keep up he good work, and thanks again!

  • I just wanted to thank you for taking the time to create theses post. It really myself and I’m sure people like me who have difficulty studying whole books and trying to figure out key points. I’ve been in this industry for 12yrs but there is so much I still don’t know. Thanks again.

  • Hello John,

    How do you calculate 0.7 times the listed spacing on a 30 and 50 foot radius? Or 2/3 smooth ceiling spacing? Thanks

  • Do smoke detectors on high ceilings (75+ feet) get de-rated?

  • Thanks for all the info. Just took and passed my level 1 yesterday. It was harder then I expected. Going to start on level 2 immediately while the rest and info are still fresh. Thanks again. Looking forward to seeing your new posts!!!

    • Congratulations Brandon,
      Yes it is usually harder then what we anticipate. best of luck for level 2, my recommendation will be to go for level 2 and 3 at the same time, if you qualify, even if you don not pass level 3 then you will have some understanding on how it is structured.

Previous Post: