AHU vs RTU: Difference and Comparison

ATU and RTU are air heating units. To be precise, RTU is a type of ATU.

Their function is to circulate purified air inside the building. The difference lies in their mounting type.

The indoors in its are already safe since they are kept inside the building but consume space. The outdoor units are robust but need proper care to function properly in weather conditions.

Hence it is known the different kinds of units. They have different internal constructions and need to be handled accordingly.


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Key Takeaways

  1. AHU stands for Air Handling Unit, while RTU stands for Rooftop Unit.
  2. AHU is installed indoors, while RTU is installed on the rooftop.
  3. AHU is suitable for large commercial buildings, while RTU is more suitable for smaller ones.


AHUs are centralized air conditioning systems used in large buildings to provide heating, cooling, and ventilation. RTUs are air conditioning systems installed on the roof of smaller buildings, containing all the necessary components for air conditioning. They are designed for ease of installation, and replacement.


AHU is defined as a device that is used to circulate and control the air in a building. It has a process of heating, ventilation as well as air conditioning.

This process is abbreviated as the HVAC system. It sets the temperature to an ideal degree which is 55 degrees Fahrenheit or 13 degrees Celsius.

On the other hand, RTU is a subtype of AHU. It is mounted on the rooftop.

It needs extra care since it is exposed to all the air and weather conditions. All its components are packaged as a single unit and are fixed on the roof. It is also a type of HVA equipment.

Comparison Table

Parameters of DifferenceAHURTU
AbbreviationIt is the short form for an air handling unit.It is the short form for a rooftop unit.
Mounting TypeIt can be mounted indoors as well as outdoors.It can only be mounted outdoors.
ProcessThey have condensation pipes attached to them.They reject the heat to the outside directly.
Set upMost of the AHUs are placed indoors and take up extra space.RTUs are set up outdoors; hence, they do not take up any inside space.
ProtectionNormal ATUs do not need extra care since they are already kept inside the building.RTUs do not need extra care since they are exposed to strong weather conditions.

What is AHU?

AHU means air handling unit. The function of an AHU is to re-condition and circulate the air to create an optimum temperature, and it is a huge metal box which is connected o the ductwork.

The main function of AHU is to collect the outside air. Pass it through the condensation unit and then supply the fresh and purified air to the building.

The ductwork henceforth channels the conditioned air through an indoor structure at the end of the process, and it returns the fresh and purified air to the room. They are used for commercial purposes.

They are extensively used with HVAC systems. It is the abbreviation for heating, ventilation, and air-conditioning.

The box comprises various components, such as. Heating and cooling elements, a fan or a blower, humidifier, mixing chambers, filters, vibration isolators, and devices for heat control.

ATUs can be indoor or outdoor units, depending on their type. There are three types of air handling units.

They are rooftop air handlers, mall air handlers, and makeup air handlers. The first is an outdoor unit, whereas the other two are indoor units.

What is RTU?

RTU stands for rooftop unit. It is an air-handling unit which is mounted on top of the roof.

They have all the components as one unit, and that is why they are often referred to as packaged air conditioners. They are more compact and budget-friendly.

They are used for commercial purposes. Mostly found on the roofs of small buildings and shops to provide air conditioning.

They are the small, compact, user-friendly, all-in-one setups of HVAC units. Their purpose is to circulate conditioned air throughout the building.

The whole setup is done outdoors. Hence it does not consume any extra space inside the building.

The units are connected to the ductwork. It provides a well-set path for the conditioning process.

They are more robust and need more care as compared to other kinds of AHUs. This is because it has to deal with the sun and extreme weather conditions; hence it needs to be weather-proof.

The compact unit includes components like the condenser, fans, evaporating coil, condenser, and compressor. The evaporating coil and fan are not separated from the condenser and compressor.

The function is very simple. It keeps the building warm during winter and cools during summer by regulating its temperature.

Main Differences Between AHU and RTU

  1. The main difference between AHU and RTU is that all RTUs are AHUs, but all AHUs are not RTUs. AHUs can be outdoor or indoor units, whereas RTUs are only outdoor units. They are mounted on top of the roof.
  2. AHU is the abbreviation for air handling units, whereas RTU is the abbreviation for rooftop units.
  3. Most of the AHUs are placed inside the building and take up extra space. On the other hand, RTUs are set up outdoors; hence, they help in space management.
  4. They have condensation pipes attached to them to carry out the condensation process for the collected air. RTUs reject the heat to the outside directly.
  5.  The common ATUs do not need extra care since they are already kept inside the building. However, RTUs do not need extra care since they are exposed to strong sun and all kinds of weather conditions.
Difference Between AHU and RTU
  1. https://www.sciencedirect.com/science/article/pii/S0306261919320616
  2. https://www.sciencedirect.com/science/article/pii/S0378778818302305
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