I'm wiring in 7 smoke detectors on 1 circuit in a home. I will link them together. The first run would be 14-2 to bring power in and the rest would be 14-3 to intereconnect them so they all go off together. This is the best way, correct? What is the best type or brand smoke detector to use?
The Golden Rule - "The man with the gold makes the rule"
That's exactly the setup that I'm using in my house. The one exception is that my wife insisted upon a combination CO/smoke detector in the garage (vehicle exhaust fears). I'm using Firex units and haven't had any trouble with them at all.
I don't know about your area but here where I am in Canada the fire department recommends they get changed out every 10 years even if they still test OK. What smoke detector you buy now might not be around at replacement time.
You may want to have the hall lights run off the otherwise dedicated smoke detector circuit. That way, it becomes obvious if the circuit breaker or other problem has the power to that circuit shut off, deactivating the smoke detectors.
I won't reccommend a brand .... while there ARE differences, there are too many other things going on; it seems that the source of supply is at least as important as the brand.
Hard wire with battery back-up? Gee, maybe someone will make that a code proposal (It already IS code, axcept for existing dwellings).
Your manner of interconnecting them is perfectly fine. NEC aside, many locales do not require smoke alarms to be on AFCI circuits; check your local rules.
As for type .... "ionization" types are cheapest, and most readily available. They are fine for most locations. Most makers also make a "photoelectric" type, which is used where there are things that can cause false alarms for the ionization type .... things like the 'plume' of hot air off the furnace, cooking vapors from the kitchen, etc.
Personally, I would not choose a combined smoke / CO detector. I have two basic reasons for this: 1) The placement of CO detectors is nowhere near as 'settled' as is the placement of smoke detectors, and I have little reason to think they should be placed in the same locations; and, 2) CO detectors have a definite 5 year life, and will simply not work 5 years after you turn them on. Smoke detectors, by comparison, are 'estimated' to last ten years (for the ionization type), and a photoelectric type might last forever (yea, right!)
Another quirk to CO detectors is that they are limited to operating at what are essentially 'normal room' temperatures. They simply aren't suited for humid or cold locations.
Personaly, I recomend Photoelectric for any dwelling unit setting. Most fires in this enviroment will start by smoldering. Ionization is more for a rapid heat type fire ( this is why they go off with steam, outside of a bathroom door etc).
I also recomend a co detector, where fossil fuels are burned. Reno, Not sure about the claim for temps, but any electronic device will have issues in the extreme.
Any life safety device should be replaced after ten (10) years.
Photos do require some maintanence, Vacuum once a year. The LED is very atractive to spiders and such in the cooler seasons, This will most definately cause "INADVERTANT" alarms. ( In this end of the trade... We don't call them "false", the detector did it's job. It just had an outside influence!
Your wireing/install plan sounds fine. As stated Heats in the garage (attached) and co detectors. Co is close to the weight of o2, so placement should be close to the smokes placement.
Standard smokes will cover 900sq ft. (15' radious from center). However the radiant rise of the smoke from a fire would dictate that the smoke be 3' from a doorway and no closer than 1 ft from the wall/corner (2' Is best).
I just cannot stress enough that smoke detectors and CO detectors are different beasts, and that fact alone argues agains incorporating them in the same device.
CO detectors are not simply "electronic." The sensing media is described by the industry as having a 'biological element.' While I have no idea just exactly what that means, the result id the same: instant alarm at freezing (so much for having one in the car or RV), and a very definite 5 year life. So, having one is an unheated garage is a bad idea.
Placement of smoke alarms has been pretty well figured out, since the 70's. I'm not quite sure what you mean by 'the radiant rise,' but no matter ... placement is pretty well explained by the instructions, and defined by code.
There is absolutely no such consensus as to the placement of CO detectors. The relevant NFPA standard simply says 'follow the instructions,' and the instructions essentially say 'put it anywhere you like.' This thread is not really the place for me to go into my ideas on the subject.
There is also an enormous difference in performance between the battery powered and line powered versions of CO detectors, and some value in the continual read-out that some models have. It's a bit hard to read that display if it's on the ceiling. Finally .... there are also a number of things that can fool a CO detector - one being natural gas itself. These complications are another reason why I resist joining CO detectors with smoke detectors in the same discussion.
Biomemetic CO detectors have a small disk of synthetic hemoglobin gel that reacts with CO to change colors. This apparently only lasts 3 years or so, and is supposed to be replaced when the battery is replaced.