I have a Crown (Waterair) "78" forced hot air system by oil. We at my household have be complaining about dizzyness and congestion. Also my daughter has had a cough for some time. I have had a oil fired tech do a CO test, and a smoke test. When doing the CO test the efficence was 70% and the CO was 9.2. He said the unit was running fine but we still are complaining about the headaches and congestion, also my daughter is still coughing. I suspect a cracked heat exchanger. I was also talking to someone who said that with a low efficency reading of 70% that they thought that was a red flag for a possible heat exchanger problem!! PLEASE HELP!