A faulty heat exchanger can cause carbon dioxide gas leaks, leading to headaches and allergy-like symptoms.

“what we didn't know was that the gas company had installed a faulty heat exchanger in this house and there was a carbon dioxide gas leak so we move in in the dead of winter and it's an energy-efficient house so the whole thing is just locked up tight and we all start breathing in these invisible fumes I get a little sick you know headaches and just some kind of allergy spring up my dad gets a little sick but we were only doing nights in the house and we were doing upstairs my mom unfortunately was doing all 24 hours in the house unpacking boxes fixing up the house fixing up the basement actually”