first you should go out today and get a digital read out Co meter
alarm, nighthawk or equivilant. make sure you are not poisoning
yourself, that little fan is pulling to much and is pulling through your
house, you definatly need more attic venting or perhaps a smaller fan.
This could make you very sick, not having your apliances vent properly.
A heating repairman can test your equipment, even your fire dept will
give advise on this. I had this problem and everything is now
powervented