How Is Makeup Air Designed for Dealership Service Bays?

The air balance is an accounting exercise with real consequences. The engineer lists every exhaust stream — general shop exhaust, tailpipe capture reels, welding and paint-prep exhaust, restroom and parts exhaust — at its design flow, then sizes makeup air to replace the total, holding the shop slightly negative to the showroom and offices but never starving. The calculation is documented as the balance schedule so future exhaust additions trigger a makeup recheck. Unit selection follows the load: direct gas-fired units where gas is available and the application suits, indirect-fired or hydronic where combustion products in the airstream are a concern, electric where gas is absent. The engineer sizes heating for the design-day temperature difference at full airflow — the worst credible hour — and verifies turndown so the units also behave on mild days.

Delivering the air well matters as much as heating it. The engineer designs low, distributed supply — ducted drops or fabric duct along the shop — so tempered air washes across technician work zones and migrates toward exhaust points, rather than short-circuiting from a single grille to the nearest exhaust fan. Discharge temperature control holds the supply in the comfort range regardless of outdoor conditions. Interlocks make the system foolproof: makeup air units start with the exhaust systems they serve and prove operation before the shop goes to work. The control sequence includes morning warm-up, occupied and unoccupied modes, and freeze protection that shuts the units down safely rather than letting coils freeze. Commissioning measures the actual balance and adjusts sheaves, dampers, and controls to the documented intent.

A complete makeup air package balances the shop honestly: • Air balance schedule totaling every exhaust stream at design flow • Makeup air units sized to match exhaust with the intended pressure cascade • Heating sized for design-day tempering with discharge temperature control • Low, distributed supply washing work zones toward exhaust points • Interlocks proving makeup air with exhaust before shop operation • Freeze protection, warm-up, and occupied/unoccupied sequences • Commissioning verification of balance with doors open and closed