We installed a 40-gallon gas fired hot water heater in 2004. The vent is a 3" pipe that goes to the chimney stack along with the vent for the gas fired heater. The 3" vent pipe is pitting and needs to be replaced. The local service company is quoting a large dollar amount to replace the 3 feet of pipe and saying it needs to be replaced with a 4" pipe to meet current building codes and that it requires refitting the vent into the chimney. If we stick with 3" pipe it is a straightforward swap. Price aside can anyone let me know what code requires assuming my town in Northern NJ doesn't deviate from the state code. I will check with town hall just wanted to get some insight in advance as it takes a day or two to get a response from the inspector.