There is no big difference between AHU and RTU; this is because RTU is just a type of AHU. AHU is the acronym for Air Handling Unit, while RTU is the acronym for Rooftop unit. AHU is a machine which helps in circulating and conditioning the air in order to create a perfect atmosphere that is not too warm or too cold. There are so many parts of AHU like cooling component, heating component, and there is a part called mixing component. Also, there is humidifier, vibration isolator and a device for heat control and recovery.
Since RTU is a type of AHU, all the various components and devices present in AHU are also present in RTU. The slight difference between them is that RTU is mostly fixed on the rooftop, and that is why it is called a rooftop unit. There are other types of AHU. They are; Makeup Air Units, Mall Air Handlers.