Heat detector in an unfinished attic

I have an old conventional fire alarm system in my commercial building. I plan on replacing it with an addressable system but I have one problem that needs to be corrected ASAP. The system has 135 degree 2-wire heat detectors throughout the building. One place is in an unfinished attic and it gets very hot there on 90+ degree days and, I believe, one heat detector has triggered twice causing the fire department to make a visit. From what I have previously read, I can simply replace it with a 194 degree heat detector. I’ve also read not to replace it with a smoke detector. Is this correct? Assuming that, are there heat detectors that somehow are marked that they got triggered? Or is this a feature of addressable systems only?

Thanks,
Kevin :slight_smile:

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Around here (Mid-Atlantic Region), I would not install a 135°F heat detector in an attic. On a nice hot summer day, you could be pushing that 135°F mark, and I’ve seen them false alarm from that. So you are within reason to want the 194°F heat detectors in your attic. I would also check a couple of other things. First, all of the heat detectors should be mounted in a electrical backbox - I prefer plastic boxes if the cabling between the detectors is FPL type (red plastic). If it’s in conduit, obviously the boxes should be metal. Too many times attic heat detectors are just screwed directly onto a joist. Second, check all the wiring running through the attic. It’s very easy for someone to step on wiring that isn’t properly protected. People get lazy, and just run the wire on top of the joists where everyone walks. I have always stapled the wire up and out of the way. Also check how the wire is fastened. It should be secured with “Romex” staples, not the small T25 staples from a staple gun. And the staples should not be “driven home”, the wire should wiggle in the staple a little. The reason why I’m putting so much focus on the wire is how the circuit works. A short ANYWHERE on the wire will case a false alarm. And as temperature changes, building materials expand and contract. That little but of a change with a wire that’s pinched, can cause the short, causing the false alarm.

Do not install smoke detectors in the attic. Too dirty, too much heat, not rated for the environment. Heat detectors are your choice. Most of the conventional heat detectors are fixed temperature or rate of rise. The fixed temperature units “pop” at their rated temperature. Literately, the disc on the bottom will fly off when activated. Then the unit has to be replaced. The rate of rise units still have the fixed element, but also incorporate a sensor that will trip if the temperature rapidly increases under a certain time frame. These have no indication that they tripped. So if your concern is pinpointing a tripped detector, stick to the fixed temperature units only.

You should be able to incorporate conventional detectors into the new addressable panel. You would need to install a module that would supervise the heat detector circuit. Put the module someplace accessible (can even be inside or next to the new fire alarm panel) to make troubleshooting easy. The only downside is that it won’t tell you exactly which heat detector was activated in the attic, only that the circuit was activated.

Wow! Thank you for your very detailed answers to my questions. Much appreciated, thanks. :smiley: