Originally Posted by
Bruce Breedlove
A TIFF is used to detect combustible gas leaks (e.g., natural gas), not CO. (Some models may also detect CO but mine only detects combustible gas.)
A tiff will detect CO as well as many other gasses, not just combustible.
Try this tip on gas furnaces. Fire the furnace upo and let run for a while. Ensure that the burner is currently lit and speed up the tiff a bit so that the ticks are faster than normal. If you stick this into the path of moving air (try fanning it with cardboard) it will slow down. If there is CO present, it will speed up. Unfortunately this also will detect styrofoam, plastic etc. in the ducts. I do carry a digital CO detector that I use if the Tiff detects anything to verify if it is actually CO and provide the buyer and HVAC tech with an actual numerical reading at the time of the inspection. If the Tiff detects something but no anctual CO is detected, it may be time to clean the dicts and retrieve the vintage hotwhells, barbies, etc.
As far as the high efficiency furnace venting. Don't forget about the fact that these are condensing furnaces and will coat the cool chimney, flue, ets with the corrosive condensate and cause possible moisture issues with the chimney and/or any surrounding objects as well as possibly leak CO due to the power vent feature.