I've got a steam heat system with radiators for my 3-family building. The hallway radiator right by the front hall entrance just seems like a total waste of energy- can I just turn the valve off? ...

The steam does not have to be trapped, because the radiator valve has an internal adjustment to allow a fixed amount of steam into the radiator which is equal to or less than the size of the radiator.

Think you already know how to use a radiator? Gelasio Lechuga has the lowdown on what you're doing wrong – and essential safety tips to follow.

This thing on the end of a radiator consists of a valve body that screws into the normal tapping, with an air vent and an actuator screwed into the body. They look a bit bulky, but are quite effective ...