PVC pipe on right is for the 90% furnace. Metal pipe on left is for the water heater. This was done as new construction and somehow passed inspection. Single wall pipe thru the wall, heater is about 4' from the wall so it is a nice, short & hot flue. Homeowner acted suprised when he was told this is improper AND unsafe, didn't seem to care since it "has been like that for years".