Provided is a wet-use plane heater using a positive temperature coefficient (PTC) constant heater-ink polymer, wherein the wet-use plane heater has unique characteristics in that it may not only be safe from the damage to the heater and the risk of fire due to self-temperature control characteristics, but a plane heater, which has been mainly installed in dry-use applications due to limitations of leakage current and induced current caused by an increase in contact area with an installation floor, may also be used for wet installation which uses a mortar.