Dedicated Outside Air Systems vs Traditional Makeup Air Units
Feb 9
4 min read
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Choosing the Right Ventilation Strategy for Performance, Comfort, and Efficiency
Ventilation design plays a bigger role than ever in large commercial and institutional buildings. Engineers are balancing indoor air quality targets, energy codes, electrification goals, and construction budgets all at the same time. The equipment selected at the start of a project can shape comfort, operating costs, and long-term system flexibility.
Two of the most common solutions for delivering outdoor air are Dedicated Outside Air Systems (DOAS) and traditional makeup air units. Both move fresh air into a building, but they support very different HVAC strategies. Knowing where NexGen DOAS systems shine and where makeup air units still make sense can help prevent design headaches later in the project.
Understanding the Difference
Dedicated Outside Air Systems (DOAS)
A DOAS unit is built to deliver 100 percent outdoor air that is fully conditioned before it enters the building. These systems are designed to manage:
Ventilation airflow requirements
Humidity and latent load control
Precise air delivery to multiple zones
With a DOAS approach, space heating and cooling are handled by terminal equipment such as fan coils, heat pumps, VRF systems, chilled beams, or radiant systems. NexGen DOAS units integrate easily into these modern designs, making them a strong fit for large buildings with multiple zones and changing occupancy patterns.
Traditional Makeup Air Units
Makeup air units are primarily used to replace air that is being exhausted from a building. They are commonly applied in spaces that require high airflow volume and consistent exhaust replacement.
Typical applications include:
Industrial facilities
Warehouses
Commercial kitchens
Process-driven ventilation systems
While makeup air units can temper incoming air, they are not built to provide the same level of zone-level comfort control or humidity management that a DOAS system offers.
Key Differences for Large Buildings
1. Ventilation Control & Code Compliance
Large buildings often struggle to maintain consistent ventilation across multiple spaces with different occupancy levels.
NexGen DOAS systems are engineered to:
Meet ASHRAE ventilation requirements
Deliver measured outdoor air to each zone
Simplify compliance in offices, schools, healthcare facilities, and mixed-use buildings
Makeup air units are typically sized to offset exhaust volume rather than manage ventilation distribution across multiple zones. This can limit flexibility in buildings with varied space requirements.
2. Humidity Management at Scale
As buildings grow larger, humidity control becomes more critical. Excess moisture leads to comfort complaints, condensation, and long-term building performance issues.
DOAS systems handle latent load centrally and supply dry, conditioned air regardless of individual zone demand. This stabilizes indoor conditions and reduces moisture-related challenges.
Makeup air units often deliver neutral or lightly tempered air, leaving humidity control largely dependent on downstream equipment. In humid climates or high-occupancy spaces, this difference becomes especially noticeable.
3. System Integration & Zoning Flexibility
Most large buildings operate across multiple thermal zones with different usage patterns and schedules.
NexGen DOAS systems integrate well with:
Fan coil systems
Heat pump equipment
Radiant heating and cooling
VRF and hybrid system designs
Separating ventilation from sensible heating and cooling improves zone-level control and allows easier system adjustments in future renovations or expansions.
Traditional makeup air units perform best in open, uniform spaces where zoning needs are minimal and airflow demands remain consistent.
4. Energy Performance & Part-Load Operation
Large buildings rarely operate at full load for extended periods. Equipment efficiency during part-load operation has a major impact on annual energy use.
DOAS systems are designed to adapt to changing airflow and load conditions. This allows connected heating and cooling equipment to operate more efficiently and supports energy code compliance.
Makeup air units often run at steady airflow rates and are less optimized for fluctuating occupancy or variable ventilation demand.
5. Electrification and Long-Term Building Strategy
Many commercial projects are planning for electrification, even if full conversion is phased over time.
NexGen DOAS systems pair well with heat pump-based designs and support all-electric or low-carbon HVAC strategies. They also integrate cleanly with electric heating and cooling equipment as building standards continue to evolve.
Makeup air units can still be part of electrified projects, but they typically offer less flexibility as system design requirements change.
Where Traditional Makeup Air Units Still Make Sense
Despite the advantages of DOAS in many large buildings, makeup air units remain the right choice for certain applications. These include:
High-exhaust industrial environments
Warehouses with continuous airflow demands
Commercial kitchens
Process-driven ventilation systems
The most effective designs match the equipment to the application rather than forcing one solution across every project type.
The Takeaway
For large commercial and institutional buildings, choosing between NexGen DOAS systems and traditional makeup air units comes down to system intent and long-term building goals.
DOAS systems are well suited for projects that prioritize ventilation accuracy, humidity control, zoning flexibility, and future-ready HVAC design.
Makeup air units remain a strong solution for replacing large volumes of exhausted air in open or process-driven environments.
Making this decision early helps avoid performance issues, inefficiencies, and costly redesigns later in construction.
How VHF Sales Can Help
At VHF Sales, we work alongside engineers and contractors to evaluate ventilation strategies based on building size, occupancy patterns, climate conditions, budget targets, and long-term operational goals.
If you’re planning a large building project and weighing DOAS versus makeup air options, our team is ready to help you size, select, and budget the right equipment with confidence.
