Heat detectors

Are they ever used in buildings with fire alarm systems that have sprinklers? I would think buildings with sprinklers wouldn’t have heat detectors since sprinklers pretty much function the same detectionwise as a heat detector. Both are set off by heat.

I know my high school has heat detectors in the kitchen even though there is some form of a suppression system in there. The rest of the school is sprinkler-less.

A lot of old buildings I’ve been in (1950s-1970s) have heat detectors installed near sprinklers. In all the ones I’ve seen the heat detectors were the Chemtronics dome shaped detectors.

This was before they had smoke detectors of course.

Nowadays, there’s a clause in the fire alarm code that says smoke / heat detectors are usually not required in low risk buildings if the building is fully sprinklered and the air ducts have detectors.

Smoke detectors are required, though, in higher risk facilities like dorms/apartments, hospitals, schools, etc.

Also, if smoke detector coverage isn’t a requirement and the building owner wants them, they can still have them installed.

My building has a Chemtronics - style heat detector in the elevator mechanical room as well as the boiler room.

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you’ll still see them in attics, mechanical rooms, elevator hoistways, and kitchens.

elevator hoistways and machine rooms, for example, will have a smoke detector and a heat detector. the smoke detector will initiate elevator recall, and bring the elevator to the ground floor and lock it out, delivering the passengers to safety.

the heat detector is expected to activate before the sprinkler and after the smoke detector. the heat detector will cause the shunt trip breaker to trip, instantly disconnecting power to the elevator motor, stopping the car if it’s still moving.

with power to the elevator disconnected, the high (30-50 gpm) flow from the machine room or hoistway sprinkler will not affect the electrical operation of the elevator motor and controls, nor will it affect the elevator car brakes. The lesser of two evils, yes, if the heat detector activated before the elevator bank was recalled, the car has passengers trapped (you cannot exit the car from the roof hatch, no matter what you saw in the movies) but at least the brakes won’t fail or the controller won’t cause erratic elevator operation - they’re trapped safely while the sprinkler controls the fire and keeps the smoke, heat, and lethal gasses to a minimum. The fire department will already be on the way, and they will see the elevator detectors in alarm and are able to perform an elevator rescue.

Codes requiring/not requiring heat detectors are not a national standard - your local AHJ may have adopted that. Overall, you’ll still see heat detectors anywhere a full detection system is installed - hospitals, nursing homes, etc, regardless of a sprinkler system. No AHJ will likely want to lessen any protection. Especially when a waterflow alarm from a sprinkler can be delayed up to 90 seconds, whereas a heat detector is an instant, unverified alarm.

I guess this makes sense. Also if the heat detector is rate-of-rise it will detect heat faster than a sprinkler will be set off by it.

Another place where I’ve seen heat detectors is my school’s stage.
This is to prevent a potential smoke machine incident.

With the exception of my middle school (which had no ceiling detectors), the schools I went to had heat sensors in many areas. My high school even had them in hallways! The K-8 school I had kindergarten at had duct smoke detectors installed in many areas (after the school was built), but it also has the dome-shaped heat detectors (rebranded by Simplex as the 4255-1) in many classroom pods, restrooms, offices, the kitchen, electrical/boiler rooms, etc. There is also unusually only ONE “regular” smoke detector in the entire school building (an old Simplex 4262 ionization heat detector) in the cafetorium.

Heat sensors also used to be very common at Massasoit Community College, but have since become rare. Only the Student Center and the Field House buildings still use heat sensors for the most part (though the Student Center does have Notifier FSP-851 smokes for elevator recall, and the Field House has Fire-Lite SD-355T detectors near the panel and in the main electrical room. Other buildings may have newer heat detectors in restrooms, but most of the others were replaced with smoke detectors over time (mostly System Sensor i3s and 2151Ts.) When they replaced the heat sensors in the Fine Arts building auditorium in early 2010 with smoke detectors, they even tested the fog machine to see if the detectors would be activated by mistake, and they weren’t, luckily.
Unusually, the Fine Arts building is also the only building on campus with sprinklers, located only in the actors’ dressing rooms and the basement (heat sensors are also present in the basement, and they also used to have them in the dressing rooms, but they were replaced in 2009 with smoke detectors…)