Why don't my heater get hot

Even though this is solved, one more thing to add.

My first car was a 73 Satellite with a 318. The heater never worked, even after replacing the core. Years later, when I yanked the engine, i found out why.
Where the heater hose goes back into the engine, it was completely clogged with rust.
Strange that the car never ran hot, but the hoses would get warm. I just gave up and froze. I was 16.