Metals are most likely because they conduct heat well
Answer:
Water heaters must have vent to the outside of the heater to remove exhaust air from the water heater, the vent go directly through it walls. It is likened to the vent in natural gas water heater which have a vent to the outside that remove by products of combustion and can also bring in air combustion.
The edifice from the hot water vent are made of metals or plastic materials depending on the venting systems.
The element you are looking for is Scandium, the 4th element in the third group.
