Rooftop Units, commonly referred to as RTUs, are self-contained HVAC systems designed to heat, cool, and ventilate buildings—primarily commercial spaces such as offices, shops, and schools. As the name suggests, they’re installed on the roof to save interior space and simplify ductwork distribution.
These compact units combine all essential HVAC components—compressors, condensers, fans, and filters—into one packaged system. Their modular design makes them easy to install, maintain, and replace compared to traditional split systems.
2. Purpose of a Rooftop Unit
The primary purpose of an RTU is to distribute conditioned air—either cooled or heated—through a defined duct network within a building.
Air is drawn into the system, filtered, conditioned to the desired temperature, and then distributed via ducts to various zones. This ensures consistent temperature control and indoor air quality, improving comfort and energy efficiency.
3. RTUs vs. AHUs (Air Handling Units)
While both systems manage air distribution, RTUs differ from Air Handling Units (AHUs) in a few critical ways:
- Location: RTUs are always roof-mounted, while AHUs are typically installed indoors.
- Integration: RTUs are self-contained “packaged” systems with built-in heating and cooling mechanisms, while AHUs often rely on external chillers or boilers.
- Durability: RTUs are weatherproof, designed to withstand harsh outdoor environments.
In short, every RTU is an AHU, but not every AHU is an RTU.
4. Construction and Housing of RTUs
The housing of an RTU acts as a protective shell, safeguarding its internal mechanical and electrical components from rain, wind, UV exposure, and temperature fluctuations.
Typically, these housings are made from galvanized steel or aluminum, with insulated panels and access doors for service personnel. This robust design ensures long-term performance and simplified maintenance.
5. Air Intake System: The Air Hood
At one end of the RTU sits the air hood, responsible for pulling in outside air. Its design helps prevent rain, snow, and debris from entering the system.
A protective mesh screen at the inlet keeps out leaves, wildlife, and other obstructions. This ensures clean airflow and prevents potential blockages or fan damage.
6. Role of Dampers in Airflow Control
Dampers are metal flaps that open and close to control airflow. Modern RTUs use motorized dampers that automatically adjust based on air temperature, CO₂ levels, or occupancy needs.
They can:
- Allow 100% fresh air in (for free cooling)
- Close completely to seal the unit
- Mix return and fresh air to save energy
7. Importance of Air Filters
Filters play a crucial role in maintaining indoor air quality and protecting system components.
Without filters, dust and dirt would accumulate on coils, fans, and ductwork, reducing performance and eventually causing equipment failure. RTUs typically use pleated or HEPA-grade filters that can be easily replaced during routine maintenance.
8. Heating and Cooling Coils Explained
RTUs rely on coils to transfer heat energy. These can either absorb heat to cool the air or release heat to warm it.
Depending on design, RTUs may feature:
- Evaporator coils (for cooling)
- Condenser coils (for heat rejection)
- Electric or gas heating coils (for heating)
Some systems even combine both heating and cooling functions into a single coil via a heat pump system.
9. Types of Heating and Cooling Systems in RTUs
There are typically three configurations:
- Cooling-Only RTUs – Ideal for warm climates, using refrigeration systems.
- Heating-Only RTUs – Used in cold regions, often with gas or electric heating.
- Combined Heating & Cooling RTUs – Versatile systems that switch modes automatically.
Hybrid versions with heat pumps can reverse the refrigeration cycle to provide both heating and cooling efficiently.
10. The Role of the Fan in Air Distribution
Fans are the driving force behind airflow in RTUs. Most use centrifugal or EC (electronically commutated) fans, which are quieter and more efficient.
The fan draws air through filters and coils, then pushes the conditioned air through ducts to various rooms, ensuring even air distribution.
11. Recirculation Systems in RTUs
RTUs with recirculation capabilities reuse a portion of the building’s return air. This helps save energy, especially during winter, by mixing warm indoor air with fresh cold air from outside.
Adjustable return air dampers regulate the mix between fresh and return air to maintain proper ventilation and comfort levels.
12. Free Cooling and Airside Economizers
When outdoor temperatures are low enough, the RTU can utilize 100% outside air for cooling instead of mechanical refrigeration—a process known as free cooling or airside economization.
This feature significantly reduces energy consumption and prolongs compressor lifespan.
13. RTUs with Heat Wheels (Energy Recovery Units)
Heat wheel RTUs incorporate a rotating heat exchanger that recovers waste energy from exhaust air.
It transfers this heat (or “coolth”) to the incoming fresh air without mixing the two streams. This improves energy efficiency and reduces heating or cooling loads—making it ideal for sustainable buildings focused on reducing CO₂ emissions.
14. Advantages of Using RTUs
- Compact and self-contained design
- Easy installation and maintenance
- Energy-efficient operation
- Space-saving rooftop placement
- Reduced ductwork complexity
- Lower installation costs
15. Common Applications of RTUs
RTUs are most commonly used in:
- Retail stores and shopping malls
- Restaurants and supermarkets
- Office buildings
- Educational institutions
- Small industrial facilities
Their modular nature allows flexibility for both single-zone and multi-zone environments.
16. Maintenance and Troubleshooting Tips
To ensure optimal RTU performance:
- Replace filters every 3–6 months
- Inspect belts, coils, and fans regularly
- Clean coils to maintain heat transfer efficiency
- Check for refrigerant leaks and proper pressure levels
- Schedule annual professional maintenance
17. Frequently Asked Questions (FAQs)
Q1. What is the main function of an RTU?
A rooftop unit conditions and distributes air within a building for heating, cooling, and ventilation purposes.
Q2. How does an RTU differ from a split HVAC system?
RTUs are single, packaged systems installed outdoors, while split systems have separate indoor and outdoor units.
Q3. Can RTUs provide both heating and cooling?
Yes, many RTUs use reversible heat pumps or dual coils to handle both functions.
Q4. What is “free cooling” in RTUs?
It’s when outside air is cool enough to be used directly for conditioning, saving energy by bypassing the compressor.
Q5. How often should RTUs be serviced?
At least once per year, though quarterly checks are recommended for commercial systems.
Q6. Are RTUs energy-efficient?
Modern RTUs with variable-speed fans, economizers, and heat recovery systems are highly energy-efficient.
18. Conclusion
Rooftop Units (RTUs) are compact, powerful, and efficient HVAC systems that play a vital role in modern commercial buildings. They combine all the essential functions of air conditioning—cooling, heating, and ventilation—into one weatherproof package.
With proper maintenance, RTUs offer long service life, low operating costs, and consistent comfort control—making them a cornerstone of energy-efficient building design.
Contact EZ Temp for all your RTU needs!