I appreciate the offers. We are looking at a tank less water heater at Menard's, The problem with it is it requires a 5" class b vent pipe, our original water heater vet is 4". is it as simple as replacing the y pipe with a 5" or is there more to it? Our furnace also vents with it. there it a 8" pipe that comes into the house and has a y that splits into 2 4" pipes.