The question that I have is this. Where is the proper placement for a co / smoke detector in the mechanical room. I was always under the impression that it should be within 6 ft. of the furnace unit on the ceiling or ceiling joist.
A to Z Home Inspection Services LLC
"Places to Avoid
Most importantly you want to avoid false positive readings from your detectors. To ensure your alarm goes off only when needed, you should place your detectors at least 15 feet away from any fossil fuel burning appliances such as:
Gas powered Kitchen Stove/Oven
Quoted from here http://www.carbonmonoxidedetectorplacement.com/
Always follow the manufacturers installation instructions that are supplied with the unit. Instructions vary between manufacturers.