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📘Rooftop Unit (RTU) Basics

📷 RTU System Diagram

 


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Figure 1: Basic RTU layout showing supply/return air, compressors, and heat exchangers.

 

🧰 What is a Rooftop Unit?

A Rooftop Unit (RTU) is a packaged HVAC system installed on the roof of a commercial building. It combines heating, cooling, ventilation, and air distribution into a single cabinet, making it ideal for spaces that lack mechanical rooms.

RTUs condition air and deliver it through ductwork connected from the roof to interior zones.

Used in:

  • Retail stores

  • Schools

  • Office buildings

  • Gyms and warehouses

🔧 Key Components

🔹 Cabinet

  • Weatherproof housing for all major components

🔹 Supply & Return Fans

  • Drive airflow through the building’s ductwork

🔹 Compressor & Refrigeration Circuit

  • Provides cooling via a refrigerant cycle

🔹 Gas Furnace or Electric Heat Section

  • Provides space heating

🔹 Economizer (Optional)

  • Allows use of outside air for “free cooling”

🔹 Filters & Dampers

  • Clean air and control intake/exhaust

 

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Figure 2: RTU maintenance access.

 

📏 Typical Specs

  • Tonnage Range: 3 to 60 tons

  • Voltage: 208/230V, 460V 3-phase

  • Mounting: Roof curb or rail

  • Airflow: Side or bottom discharge/return

🧱 Installation Considerations

 

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Figure 3: RTU being installed on curb via crane lift.

 

  • Requires roof curb and structural reinforcement

  • Duct cutouts must match RTU supply/return layout

  • Condensate drain and electrical connections needed

  • Consider local code compliance (curb height, seismic, clearance)

🧼 Maintenance Requirements

 


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Figure 4: Service panel access for quick maintenance.

 

✅ Advantages

  • All-in-one solution (heat, cool, ventilate)

  • Saves indoor mechanical room space

  • Easy access for service via roof

  • Works well with zone VAV systems

⚠️ Disadvantages

  • Requires crane for installation

  • Exposed to weather—must be maintained

  • Large units may require roof reinforcement

  • Not ideal for multistory duct risers

🛠️ Common Issues

  • Tripped high-pressure switch

  • Dirty condenser coil reducing efficiency

  • Worn fan belts causing poor airflow

  • Economizer failure (stuck damper or sensor fault)

📎 Training & Resources

🧠 Summary

RTUs are versatile, self-contained HVAC systems ideal for commercial buildings needing reliable, rooftop-mounted climate control. They simplify installation, reduce mechanical room needs, and are accessible for service—making them a go-to option for many HVAC designs.

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