There are two types of tumble dryer, including condenser and vented models. Condensers work by separating moisture from the air and storing it in a water container. You’ll need to empty this container after each cycle. Vented models come with a large hose that’s designed to transfer the moist air outside. This saves you having to empty a container, but may require some installation if you wish to vent through a wall.
Think about where you're going to put your new tumble dryer before you buy. Keep in mind that it may not heat up as it should if it has to withstand cold temperatures in a garage or other outdoor space. The product manual will tell you the recommended operating temperatures, so it's worth a quick read.