How Do You Design Makeup Air for Exhaust-Heavy Buildings?

Makeup air design replaces exhausted air with tempered, filtered outdoor air to maintain proper building pressure relationships. The engineering covers a complete building air balance, makeup air quantity and tempering strategy (heating, cooling, energy recovery), distribution locations that avoid short-circuiting to exhausts, and controls that track exhaust operation — including variable exhaust systems. The mental model is simple: buildings are not sealed boxes, and exhaust without makeup is a vacuum cleaner attached to the envelope. Designing the replacement air path deliberately — instead of letting it infiltrate through cracks — is what separates engineered buildings from problematic ones.

I treat the building air balance as a first-class design deliverable, not a contractor's field exercise. It tabulates every supply and every exhaust — HVAC supply, kitchen hoods, toilet exhaust, process exhaust, infiltration allowances — and shows the resulting pressure relationship for each zone and the building overall. On complex facilities this is a spreadsheet with dozens of line items, and it gets updated as the design evolves. Distribution design follows the balance. Makeup air should be introduced where it serves the space — near the exhaust source but not so close it short-circuits, tempered enough not to create comfort complaints, and distributed to avoid dead zones. In kitchens, introducing makeup air through perforated diffusers around the hood perimeter improves capture; dumping it across the room wastes it. These are design decisions with measurable performance consequences.

Good makeup air design is invisible — the building just works: doors open normally, hoods capture, pressures hold. Getting there requires covering the fundamentals. What every makeup air design needs.

• Complete air balance: every exhaust and supply tabulated with resulting zone pressures
• Tempering strategy: heating and cooling approach justified by climate, application, and energy code
• Thoughtful distribution: introduction points that serve the space without short-circuiting
• Tracking controls: makeup air following variable exhaust via pressure or direct tracking
• Energy recovery evaluation: exhaust heat recovery where volumes and runtimes justify it