Heater Core Inlet and Outlet [How to Tell Apart]

If you are changing the heater core then you need to know which is inlet and outlet.

The warm hose connected to radiator is outlet. The other one is the inlet.

Video explaining that they are not labelled and how to know which is inlet:



A heater core is a device that heats the vehicle cabin by transferring some heat from radiator. Here is what one looks like: