Cause its bleedair and not combusted air the CO level should be of no concern
that's what they said many years ago about the problems of the exhaust gases and particulates - 'the wrong size to cause health issues' they said - it's the same particulates that are being blamed fro inner city pollution and poor air quailty.....
Having the heating on for extended periods always left me feeling flush-faced and with a slight headache - classic symptoms of mild CO poisoning - some of the air came from around the combustion chamber ISTR.