All the Thetford Compressor fridges are surrounded by a frame that has a built-in vent at the top or bottom of the fridge. This vent is used to expel warm air that has passed over the cooling unit system. The cooling unit system is built into the rear of the fridge. Cool air is pulled through the bottom of the fridge and passed across the cooling unit. The warm air is expelled out of the top vent on these models: T1090, T1152, T1274, T2152. The warm air is expelled out of the bottom vent on the T2175.
Please see Product/Installation Manual for more information.