There are two types of tumble drier - condenser and vented.

Philip - if your machine is just a drier with the hot air escaping through a hose into a hole in the wall, then it's vented.

The condenser type is when you have a combined washer/drier. It uses the condensing system because a hose into a hole in the wall would make a big puddle outside when you're using the machine on a wash cycle!