Any unauthorized changes can compromise the safety of the units, AHRI officials said, potentially exposing homeowners to carbon monoxide. 

The Air-Conditioning, Heating and Refrigeration Institute is telling consumers to stay away from altering gas furnaces themselves or permitting contractors to make unapproved changes.

Any unauthorized changes can compromise the safety of the units, AHRI officials said, potentially exposing homeowners to carbon monoxide or other harmful gases. Always check with local manufacturer’s representatives before OKing any modifications.

“Any unauthorized modification to a gas burning appliance voids its safety certification and may expose consumers to a risk of property damage, personal injury, or even death," said the institute’s chief technical adviser, Frank A. Stanonik.  "AHRI is committed to providing consumers with information on the proper installation and safe and efficient use of gas-fired appliances.”