The uncased, 1.5–5 ton 4PXA coil is designed for upflow installations. Also known as an evaporator coil or an indoor coil, this piece is the unsung hero of your heating or cooling system. Our all-aluminum coils are designed to work with your outdoor condensing unit or furnace. They are matched in size, efficiency and capacity to ensure optimal performance of your home comfort system. The coil serves as a heat exchanger—working with your heating system in the winter and your cooling system in the summer—featuring a new, enhanced fin design for greater heat transfer.