Yes, plecos need a water heater. Plecos are tropical fish and do best when kept in warm waters between 75-82 °F (24-28 °C). A heater is necessary to maintain this temperature range as the ambient air temperature may not be enough to keep them at an ideal level. If you have a large tank, it can help to use two heaters so that there’s one on each side of the tank allowing for more even heating. Additionally, some owners choose to use an aquarium chiller during summer months or if they live in warmer climates where temperatures get higher than 82°F (28°C). While plecos don’t require any additional lighting set up other than what would normally come with your aquarium setup, their natural habitat often includes lots of hiding places such as caves or logs which should also be provided if possible. Finally, since many pleco species grow quite large, tanks over 50 gallons are recommended for these larger species while those under 4 inches can happily stay in smaller tanks around 20 gallons or more depending on bioload and filtration needs.