P1 also known as Type 10, is a type of radiator with 1 radiator panel and no convection fins.
K1 also known as Type 11, is a type of radiator with 1 radiator panel and 1 set of convection fins.
P+ also known as Type 21, is a type of radiator with 2 radiator panels and 1 set of convection fins.
K2 also known as Type 22, is a type of radiator with 2 radiator panels and 2 sets of convection fins.
K3 also known as Type 33, is a type of radiator with 3 radiator panels and 3 sets of convection fins.