1.fan of forced exhaust 2.apply to7L, 8L,10L,12L,13L,14L,16L,18L,20L's capacity 3.plastic and metal of raw materials 1.fan of forced exhaust 2.apply to7L, 8L,10L,12L,13L,14L,16L,18L,20L's capacity of balanced type(constant temperature type)3.plastic and metal of raw materials gas water heater parts