I recently installed a 40 gallon GE natural gas water heater in my basement. I was planning on getting this inspected this week. I hooked it up and turned everything on after checking connections, etc. Everything was fine until today. It has been running for ~4 days. Today I noticed a smell in the house that seems to be stronger near the basement. I have a CO monitor down there and it hasn't gone off and when tested it reports 0 ppm. I've double checked the gas connections, and this definitely doesn't seem like a natural gas smell. I have it currently turned off at the valve on the gas line. I'm thinking this may be some sort of spill from the vent, but I can't figure it out. The vent rises about 1/2 inch in 10 inches into a brick chimney. It rises slightly less than the original water heater because the new one is taller. Per the inspectors requirements I installed 2 100 sq inch vents in the wall to provide combustion air into the room. I've soaped all the connections and no bubbles, and conducted the flue spillage test as outlined in the installation guide. My clothes dryer is in the same room. No issues with the older water heater. This has me a little freaked out and I'm thinking of just switching over to an electric model for peace of mind. Higher costs though. I'm also considering renting the home in the future. Any thoughts?