Micro-Roaster Head-to-Head

By Mateo García · Reviewed by Yuki Tanaka · Updated 10 Mar 2026

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 matrix for this setup task
OptionWhen to useNotes
Roof stack directSingle-storey bayLowest static loss
Horizontal run to wall fanMulti-tenant buildingCheck lease restrictions
Afterburner inlineStrict emission limits+15% CFM, +$18k USD

Step-by-step procedure

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

This setup guide supports roaster selection and install decisions documented in our head-to-head comparisons.

Frequently asked questions

Q1: Can W6A share exhaust with café HVAC?
No — dedicated roast exhaust required. Chaff and VOC load contaminates general HVAC.
Q2: What filter before fan?
Giesen cyclone separator standard; add baghouse only if local code requires PM limits below 50 mg/m³.
Q3: EU vs US stack codes?
EU references EN 13792 for coffee roasting emissions; US uses local BACT. Netherlands often requires afterburner in urban zones.
Q4: How often to clean duct?
Inspect quarterly; full chaff clean every 500 roast hours or 6 months, whichever first. NFPA 664 applies to combustible dust.

References

  1. Giesen Coffee Roasters. "W6A installation manual GEX-W6A-2024." Accessed 10 Mar 2026. giesen-coffee-roasters.com/support/
  2. NFPA 82. "Standard on Incinerators and Waste and Linen Handling Systems." 2024 ed. Accessed 10 Mar 2026. www.nfpa.org/codes-and-standards/nfpa-82

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