By Kai Nakamura · Production roaster & equipment editor · Updated 2026-09-17
How to Design a Commercial Roaster Exhaust System for Giesen W6A
The Giesen W6A requires 520 CFM minimum exhaust at the stack connection per Giesen factory spec (document GEX-W6A-2024).
Exhaust design must account for afterburner add-on (+15% CFM), make-up air, and local AHJ separation distances from air intakes. This guide sizes ducting, fan static pressure, and make-up air for a typical 6 kg production roastery bay.
Decision box
| Option | When to use | Notes |
|---|---|---|
| Roof stack direct | Single-storey bay | Lowest static loss |
| Horizontal run to wall fan | Multi-tenant building | Check lease restrictions |
| Afterburner inline | Strict emission limits | +15% CFM, +$18k USD |
Procedure
Step 1: Confirm CFM requirement
Base W6A: 520 CFM. Giesen afterburner option: add 78 CFM (15%). Size fan at 110% of total for filter loading degradation over 6 months.
Step 2: Calculate duct diameter
At 600 CFM and 10 m/s velocity, minimum round duct ID = 180 mm (7"). Rectangular equivalent: 200 × 150 mm. Reduce elbows — each 90° adds 0.3" static loss equivalent to 3 m straight run.
Step 3: Select fan and motor
Target 1.2" WC static at fan inlet. Typical selection: backward-inclined centrifugal, 0.75 kW motor, VFD for balance. Avoid axial fans in chaff service — clogs blade pitch.
Step 4: Design make-up air
Provide 510 CFM make-up (85% of 600) via dedicated louvre or HVAC interlock. Negative pressure > 5 Pa in roast room pulls café odours into drum — unacceptable for QC.
Step 5: AHJ submission and install
Submit Giesen exhaust diagram, fan curve, and separation distances. Typical US requirement: 3 m from air intakes, 1 m above parapet. Schedule pre-inspection before insulation wrap.