Two questions:
1) What is the standard that covers installation of CO detectors in homes?
2) What is the best location? (I have seen the combo fire/co detectors on the market, but I am not convinced that CO and smoke are distributed in the same manner).

Question 1: NFPA 720.

Question 2: Carbon monoxide has the same vapor density as air (1.0), meaning that it neither sinks nor rises. In my opinion, it is a crap shoot as far as location goes. Here in Utah they are required in new dwelling units, and I typically see the combonation type (c/o plus smoke) installed, so they are always at the ceiling.

I bought two to go in my home. After reading the instructions on where not to locate them, I had to return them where I bought them, because it said not to put in within certain area near an air return, or near an entrance, near any gas appliance, etc. The way my house is laid out, there was no place for them Maybe another brand might work? Steve

Thanks, Ryan. I am inclined to place one at sleeping-to-thermostat level, near the beds. After all, aren't we primarily concerned with the risk while we're sleeping?

An earlier experience, with a first-generation model, had nuisance tripping from the "bloom" of gas released when the wall-mounted heater kicked on. I believe that the unit was located too close to the heater, and the tendency of the "bloom" to rise before dispersing contributed to the problem. (The heater has a direct outside air source, as well as a direct vent).