A Dedicated Outdoor Air Systems (DOAS) is a ventilation system that handles a building’s fresh air requirements separately from its space heating and cooling equipment. Rather than relying on a single system to both condition indoor air and bring in fresh outdoor air, a DOAS is designed specifically to treat and deliver ventilation air — supporting indoor air quality without forcing the primary HVAC system to do double duty.
How Does a DOAS Work?
Dedicated outdoor air systems draws in outdoor air, conditions it (typically dehumidifying it and adjusting temperature), and delivers it directly to occupied spaces, while a separate system handles the building’s sensible heating and cooling load. Because ventilation and space conditioning are decoupled, each system can be optimized for its specific job rather than compromising on both at once. Many DOAS units also incorporate energy recovery ventilation (ERV) or heat recovery ventilation (HRV) technology, which captures energy from the outgoing exhaust air stream and uses it to pre-condition incoming outdoor air — reducing the energy cost of ventilation significantly.
Why Use a DOAS Instead of a Standard HVAC System Alone?
Standard HVAC systems are primarily designed to manage temperature, and ventilation is often treated as a secondary function layered on top — which can lead to inconsistent humidity control, uneven air quality, and wasted energy conditioning more outdoor air than necessary at the wrong times. A DOAS addresses these gaps directly:
- Improved humidity control — a DOAS is specifically engineered to dehumidify incoming outdoor air, which is one of the most common weak points in standard HVAC ventilation.
- Better indoor air quality — because ventilation is handled by a dedicated, precisely controlled system, buildings can consistently meet fresh air requirements rather than depending on a shared system to balance ventilation against temperature control.
- Energy efficiency — energy recovery components reduce the cost of conditioning outdoor air, and decoupling ventilation from space conditioning allows each system to run more efficiently at its specific task.
- Reduced load on primary HVAC equipment — with ventilation handled separately, primary heating and cooling equipment can be sized and operated based on the building’s actual sensible load, rather than oversized to compensate for humidity and fresh air demands.
- Consistent code compliance — a dedicated system makes it easier to verify and maintain compliance with ventilation standards, since air changes and fresh air delivery aren’t dependent on how the primary HVAC system happens to be cycling.
What Facilities Benefit Most from a DOAS?
DOAS installations deliver the most value in facilities with high ventilation requirements, tight humidity control needs, or variable occupancy that makes shared ventilation and conditioning inefficient. Common applications include:
- Schools and educational facilities, where consistent fresh air delivery supports both air quality and code compliance
- Healthcare and senior living facilities, where humidity control and air quality directly affect occupant health
- Multi-family buildings, where individual unit ventilation needs to be delivered consistently and efficiently
- Restaurants and food service facilities, where makeup air requirements from kitchen exhaust hoods create significant ventilation demand
- Office buildings and commercial real estate, particularly in high-density or high-occupancy spaces
- Manufacturing and industrial facilities with specific air quality or humidity control requirements
- Any facility pursuing LEED certification or aggressive energy efficiency goals, since decoupled ventilation is a recognized strategy for reducing overall HVAC energy use
DOAS and Building Automation
DOAS are often integrated with a building’s automation system, allowing facility managers to monitor and adjust ventilation rates, humidity levels, and energy recovery performance alongside the rest of the building’s HVAC operations. This integration supports both energy efficiency and easier troubleshooting, since ventilation performance data is available in the same place as the rest of the building’s HVAC data.
Installation, Maintenance, and Service
Level One HVAC provides full lifecycle support for commercial DOAS installations, including:
- System design and sizing — calculating ventilation requirements based on occupancy, code requirements, and building use to properly size dedicated outdoor air systems for your facility.
- Installation — coordinated installation designed to integrate cleanly with existing HVAC infrastructure and minimize disruption to building operations.
- BAS integration — connecting DOAS performance data and controls to your building automation system where applicable.
- Preventive maintenance — routine inspection of energy recovery components, filters, coils, and controls to maintain performance and efficiency over time.
- Repair — diagnosing and resolving issues with airflow, dehumidification performance, or energy recovery components.
Frequently Asked Questions
What’s the difference between a DOAS and a standard rooftop unit? A standard rooftop unit typically handles both space conditioning and some ventilation together, while a DOAS is dedicated specifically to treating and delivering outdoor air, working alongside a separate system that handles space heating and cooling.
Does a DOAS save energy compared to standard ventilation? Yes, in most cases. Energy recovery components capture energy from exhaust air to pre-condition incoming outdoor air, which typically reduces the energy cost of meeting ventilation requirements compared to conditioning 100% outdoor air without recovery.
Is a DOAS only useful for large commercial buildings? No. While DOAS are common in large commercial and institutional buildings, they’re also used in multi-family buildings and smaller commercial facilities with specific humidity control or air quality needs.
Can a DOAS be added to an existing building? Yes. DOAS can often be integrated into existing buildings as part of a renovation or HVAC upgrade, particularly when a facility is looking to improve indoor air quality or address humidity control issues with its current system.
Request a DOAS Assessment
If your facility is dealing with humidity control issues, inconsistent air quality, or you’re planning a new construction or major renovation project, a Dedicated Outdoor Air System may be worth exploring. Level One HVAC can evaluate your building and recommend a ventilation strategy that fits your facility’s needs.
Contact us today to schedule a DOAS assessment or consultation.
Serving all of Michigan
Toll Free: 844-616-4822
Grand Rapids: 616-616-4822
New Hudson: 248-486-6500
West Branch: 989-999-4822