A house carbon monoxide detector has a 0-999ppm meter, Dont know how this
will corrospond with percentage of CO though. I duct taped one to my
expantion tank opening to see if I was getting any CO in my exhaust. I cut
open a 1 gallon milk jug and placed it inside and then taped it shut and to
the tank opening. Then  Iplugged in the extention  cord and waited. No CO
was present.Do you suppose one could place a meter near the exhaust and get
an accurate ppm of CO, without melting the detector?