Heat transfer within a solid material, such as a metal tube wall, occurs via conduction.
Conduction describes heat transfer occurring within a solid or between solids in direct contact.
In refrigeration and air conditioning coils, heat traverses the metal tubing wall by conduction.
Subsequently, convection transports heat to or from the fluid internal or external to the tube.
Radiation is the transfer of heat via electromagnetic waves, requiring no contact.
Transmission is a broad term, not a specific technical mode of heat transfer.
Therefore, conduction is the accurate description for heat flow through metal.