Difference Between AHU and RTU (With Table)

The full form of AHU is Air Handling Unit and the full form of RTU is Roof Top Unit. Both of these circulate air and control its processing. Both of these are very similar to each other and have mostly similar components, but some properties make them different from each other.

AHU and RTU are water-cooled chillers. RTU is a type of AHU. But there is something that differentiates them.


The main difference between the AHU and the RTU equipment is that the AHU helps in circulating and conditioning the air. On the other hand, the RoofTop Unit is a type of Air Handling Unit in which RTU is fixed at the rooftop of the box.

A huge metallic box, which creates an ideal environment by circulating and conditioning the air, is termed Air Handling Unit. The AHU has a fan or a blower, filters, mixing chambers, cooling elements, and heating elements. There are three types of RU present in the market, whose names are Mall Air Handler, Makeup Air Handlers, and RoofTop Handling Unit.

A RoofTop Unit has similar components, the only difference is that it is kept on the rooftop of the box. It is an outdoor Air Handling Unit. As in other types of AHU, it does not create extra spaces for fitting.

Comparison Table Between AHU and RTU

ComponentsThe components of AHU air filter, heating or cooling elements, humidifier, mixing chamber, fan or blower, balancing, heat recovery device, controls, vibration isolators, sound attenuators, The main components of the RoofTop Unit are – an air-cooled condenser, evaporator, compressor, and expansion device. 
PlacementThe AHU is placed inside the building and does not need any special care. The RTU is placed on the roof of the building. Therefore, it needed special care as it is exposed to the weather.
SpaceThe AHU is placed indoors therefore it is important to create extra space for it. The RTU is mounted on the roof of the building. Therefore, there is no concern about creating extra space.
SystemIt is one part system and requires another part to move anything other than the air.It has all the components fixed in one packet. There is no need for a second system.
Full-Form Its full form is the Air Handling Unit. Its full form is RoofTop Unit.

What is AHU?

An air handling unit is a device made for controlling, regulating, and circulating air for heating, air-conditioning, and ventilating systems. It is usually made up of a large box that contains filter tracks, a cooling system, a heating system, chambers, dampers, sound attenuators, and a blower. 

The air handlers of this device are connected to the ductwork ventilation system, whose work is to distribute the conditioned air to every part of the building and return the air to the air handling unit. Sometimes it transfers and returns the air directly from the space provided. 

Terminal units are small air handlers for use. This part includes only an air filter, blower, and coil. The fan coil unit or blower coil is called a simple terminal. There are different types of AHU. The larger air handler that does not contain any recirculated air is termed Makeup Air Unit (MAR) or FAHU (Fresh Air Handling Unit). The air handler that is designed for outdoor use, typically for roofs, is termed Heating and Cooling Unit or PU (Packaged Unit) or RoofTop Unit (RTU).

What is RTU?

The RoofTop Unit or RTU is a kind of HVAC. In a small box, it contains all the needed parts to provide conditioned air such as an air-cooled condenser, evaporator, compressor, and expansion device. 

This rooftop unit connects directly to the ductwork system, whose work is to distribute the conditioned air to the surrounding and return the air to the rooftop unit.

The unit is ventilating when the conditioned air returns to the rooftop. In some of the units, the returning air and the outdoor air are mixed up to produce fresh air. The air now will move through the filters. From here, it will move to the cooling coil. The cooling coil chills air by running it through the refrigerant. The refrigerant then gets cooled by a process known as the standard refrigerator cycle. The cooled air will blow through the bower. From here, the air gets conditioned and ready to leave for space. 

In some of the units, for further adjusting the air humidity, small heating elements are present near the blower. In this unit, there is a presence of clear and insulated divide between the evaporators coils. Its work is to cool the return air. The compressor coils and the condenser eject heat into the atmosphere.

Main Differences Between AHU and RTU

  1. Air Handling Unit is the full form of AHU. On the other hand, the full form of RTU is RoofTop Unit. 
  2. AHU is an air controlling and regulating device used inside the building. On the other hand, RTU is a type of AHU that is used outside the building such as the roof.
  3. Air Handling Unit is more than one system package. On the other hand, RoofTop is one system package.
  4. Both devices regulate air, but AHU needs space. On the other hand, there is a concern for space in RTU.
  5. RTU is just a kind of AHU. On the other hand, AHU is one of its kind.


Most people think that the RTU (RoofTop Handling Unit) and the AHU (Air Handling Unit) work the same. To one point, it is true. As both of these do the work of circulating and controlling the air. And both of these sucks the air and pass it through the cooling coils. But some properties create differences between them. To protect oneself from future confusion, It was important to know the differences between the AHU and RTU.


  1. https://www.sciencedirect.com/science/article/pii/S0378778803001178
  2. https://www.sciencedirect.com/science/article/pii/S0378778818302305