On Monday, January 8, 2018 at 2:14:34 PM UTC-5, wrote:
Low or high?


Neither.

https://www.safety.com/carbon-monoxi...lacement/#gref

The instructions that came with my Kidde CO detector said to place it on a wall at least six inches from the ceiling to avoid dead spots. The "high" recommendation is that the CO you're detecting is almost certainly a product of combustion, therefore heated and (a little) lighter than air.

At a customer site, the fire inspector said I needed to install a CO detector outside the boiler room. I asked him how high to place it on the wall, and he was pretty well stumped, as if he had never thought about it before. Gave me a real warm fuzzy feeling.