Traditional Vented Dryer
Traditional vented dryers draw in room temperature air from your laundry room, heat it, tumble your clothes in it, and then blow the exhaust—full of evaporated moisture—outside.
Condenser dryers draw a small amount of air into the dryer—much less than is needed in a traditional unit. The air passes through the condenser for initial heating. The heated air is then pushed into the drum, where it heats up the wet laundry and causes water to evaporate. Instead of venting that hot, wet air outside, the air is looped back into the condenser where it's cooled down. The evaporated water either goes down the drain, or collects in a tray that the user must empty after a cycle. Since condenser dryers don't get as hot as vented models, they can also be more gentle on clothes.
Heat Pump Dryers
These ventless machines replace the condenser with a heat pump, which works like an air conditioner running in reverse: As they recirculate hot air in the drum, they also remove moisture from laundry. Heat pump dryers are more efficient, since they can achieve the same result at even lower temperatures than a condenser. The average heat pump dryer uses half as much energy as a vented model, but they also take longer to get your clothes dry. A vented dryer might finish a Normal load in about 45-50 minutes, but a heat pump dryer could run for an hour and a half. Bulky items like a blanket or comforter could be more than three hours. The clothes also come out of the dryer much cooler than other dryers, barely warmer than room temperature.