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I've just moved into a new house and it doesn't have a smoke alarm on the main floor yet. The main floor is a long rectangular open concept design, with living room at the front near the front door, kitchen at rear with rear door, and dining in between. About 37 feet long, and 12 feet wide for the most of the length. I'm trying to figure out a good number of fire alarms and where to place it/them.

Here is a rough sketch, side and top view, not to scale:

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Those stairs go up to the second floor and have an alarm at the top already, i.e. in the upper hallway. I see three candidate locations: A,B, and C. Based on what I've read online, it seems alarms are not recommended right in the kitchen area (too many false alarms?), so I'm leaning away from A. I'm seeing recommendations to have an alarm in both the dining and living room, but in my case those are one continuous space. So I'm wondering should I do B (middle of the house length-wise), C (front of the house, further from kitchen, or both? Or all three?!?

Note that there's a bulk-head with some duct work that segments the ceiling of the kitchen from the rest of the floor. It spans the width of the main floor.

Thanks in advance.

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  • How wide is the duct soffit between the kitchen and the dining room?
    – ThreePhaseEel
    Aug 3 '20 at 23:42
  • @ThreePhaseEel It's about 2'8". I've updated my sketch. Thanks.
    – SSilk
    Aug 4 '20 at 13:19
  • I would put it right between B and C.
    – Z4-tier
    Aug 4 '20 at 18:44
  • and test it with windows open and closed: burn some paper in an old pot, placed on the stove. Keep the lid and some water handy.
    – P2000
    Aug 4 '20 at 20:39
  • @P2000 I wouldn't go that far -- easy to create a bigger problem than you're trying to solve that way, I reckon. (If nothing else, imagine trying to get the smoky smell out of the house...)
    – ThreePhaseEel
    Aug 4 '20 at 23:54
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I would place it halfway between B and C as well

I would place the smoke alarm halfway between B and C, or in other words, about in the middle of the living/dining space. If we look at the NFPA 72 prescriptive criteria for smoke alarm/detector siting, we first note that we can't place the alarm within 10' of the range (29.8.3.4 point 4), which means that A is right out. This is indeed for the reason you state: a smoke alarm in a kitchen would have far too many nuisance alarms to be useful, even though modern alarms are better at rejecting nuisance smoke than older units thanks to enhanced UL testing.

Likewise, B would be a bit nuisance-alarm-prone as well, as it's within the 20' radius that requires enhanced nuisance smoke rejection, while C is out of range of the back of the dining area. (No point in the room can be over 21' away from a typical smoke alarm as per the 17.3.2.3.1 point 2 prescriptive criteria.) As a result, roughly midway through the living/dining area is probably going to be the best place for the smoke alarm to go.

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