Placement of heat detectors in garage

[newalarm]

I was starting my install of heat detectors in my garage. The inside is CMU with exposed roof joists. There is a slight slope on garage. We have typical roll up (sectional) garage doors. My first thought was centering them in the garage bay at highest part of  ceiling, on the ceiling, but thought it was probably a bad idea due to when garage door is open, it may take longer to trigger. I read that you can place them on wall, 6"-12" from ceiling (or bottom of joist in my situation?)
 
Any thoughts or recommendations?
 
Thank you.

 

[Del91574]

Ceiling is better due to spacing.
 
If you have a ROR unit the OHD's affecting the units should be minimal. Really, how long are you intending on leaving the doors open?

 

[newalarm]

Probably not long. And they are really there to catch something that might happen while we are away, or have stepped away. We have three garage doors and I was going to place them at the highest part of each ceiling, at bottom of the joist, about 12" away from the wall. Highest part of ceiling is near the OHDs.

 

[Del91574]

They should not be placed near the wall. The best location is centered on the room....they get a 30' radius detection for almost every one I know of.
 
Assuming a normal car sized "bay" or maybe a little deeper, they should be placed as close to center as possible.

 

[ano]

I may be going out on the limb with this one, but you may want to install your heat sensors by items in your garage that could potentially catch on fire. A water heater, furnace, over your car hood, above where you store flamable liquids, etc.  You can't catch everything, but if you know potential problem spots, I'd definitly take that into consideration.

 

[newalarm]

Del, Garage is 35' long by 20 deep, with two garage doors on the long side. Would you still locate them in center if there was a slope to the roof/joists? It is essentially a flat roof with enough slope to get the water off, 1/4" per foot more or less.
 
Ano, I don't have any particular fire starting devices. I would assume it could start anywhere.

 

[ano]

Ano, I don't have any particular fire starting devices. I would assume it could start anywhere.

Unless you know something about spontaneous combustion that I don't, fires don't just start from nowhere. If you don't have any heat sources in your garage like a water heater, that pretty much leaves your car (which could combust) or electric wiring, so keep that in mind when planing sensor layout. Although the sensors don't need to be close to the fire start source to work, it sure does give you a quicker notification. It may mean the difference between catching the fire at the very start, vs. after your garage is fully in flames.

 

[NeverDie]

I was starting my install of heat detectors in my garage. The inside is CMU with exposed roof joists. There is a slight slope on garage. We have typical roll up (sectional) garage doors. My first thought was centering them in the garage bay at highest part of  ceiling, on the ceiling, but thought it was probably a bad idea due to when garage door is open, it may take longer to trigger. I read that you can place them on wall, 6"-12" from ceiling (or bottom of joist in my situation?)
 
Any thoughts or recommendations?
 
Thank you.

 
This seems like it may well provide the steering you're looking for:
https://www.inkling.com/read/nfpa-72-national-fire-alarm-signaling-handbook-2013/chapter-17/17-6-heat-sensing-fire-detectors
 
In particular, notice section 17.6.3.4* Sloping Ceilings (Peaked and Shed) and whatever subsections match your situation.
 

 

[Del91574]

Del, Garage is 35' long by 20 deep, with two garage doors on the long side. Would you still locate them in center if there was a slope to the roof/joists? It is essentially a flat roof with enough slope to get the water off, 1/4" per foot more or less.
 
Ano, I don't have any particular fire starting devices. I would assume it could start anywhere.

Technically the space would only necessitate 1 for 100% coverage (900 sq ft), but in the interest of coverage, you'd technically place one at about the 11' mark and a second at the 22' mark at 10' centerline.
 
The location is insignificant as far as what would pick up "faster" contrary to what is stated. If you require something that is faster acting, you pick up a combination ROR and fixed unit.

 

[newalarm]

The thermals I am using are system sensor 5602 (194F RoR). I have used the lower (135F i think) 5601P in other parts of the house, but since garage can get hot in summer, and i weld, i thought the 194 would be safer.
 
So essentially, I should not be too concerned with OHDs, even if open, and the slope is not significant enough to affect sensors. Is that right? I will locate on bottom of joists.
 
Thanks for location tip DEL.

 

[Del91574]

Thermals should be selected to be at least 20 degrees above the highest ambient temperatrure possible in the space. Picking one that is too high a temperature would be a poor design choice.

 

[newalarm]

That is the tricky part. In uninsulated space (attic or garage), You would have to wait till the hottest day on record to measure. Unless I take a reading inside, and outside on a warm day and calculate difference. Then look at hottest day on average in the area and add the difference.
 
Our attic crawlspace is not very accessible unfortunately, making this more difficult. I bought a thermal to go there as well.

 

[Desert_AIP]

My attic will get above 120 in summer, and I'm in Washington.
Almost anyplace else will get hotter.
I used 194s in the attic.

Heat of combustion for wood is ~400 degrees.

 

[newalarm]

DC or state? That would be big difference in temp i would think.

 

[Desert_AIP]

State
I'd expect D.C. to top 150 in summer.
 
That's in the attic space.
The 194s may be a bit high, I was worried about a heat spike on an abnormally hot day (90s) going over 150 and tripping the lower rated sensors.
 
In the interior of a garage or shop, I use a lower rating like ~150 IIRC.