By Kai Nakamura · Production roaster & equipment editor · Updated 2026-09-17
How to Size and Install an Afterburner for a 12kg Commercial Roaster
Afterburners for 12 kg-class gas roasters (Diedrich IR-12, Probat P12 III, Mill City 10kg scaled) typically operate at 1,400–1,800 °F combustion chamber temperature with 0.5–0.7 s residence time to destroy coffee roasting VOCs.
Sizing ties to roaster exhaust CFM (900 baseline for IR-12) plus 15% headroom — this guide covers thermal input, electrical service, and regulatory triggers in US and EU jurisdictions.
Decision box
| Option | When to use | Notes |
|---|---|---|
| Catalytic oxidiser | Low batch frequency | Lower gas, higher capex |
| Thermal afterburner | Production volume > 300 kg/wk | Industry standard |
| Integrated (Loring) | New Loring purchase | Factory matched CFM |
Procedure
Step 1: Determine regulatory requirement
Check local BACT guidelines — California SCAQMD Rule 1133 applies to coffee roasting > 10 kg/batch in some districts. EU IED annex cites 50 mg/Nm³ PM limit in dense zones. Permit first, purchase second.
Step 2: Match CFM to roaster outlet
Diedrich IR-12: 900 CFM roaster + 135 CFM afterburner addition = 1,035 CFM fan total. Loring integrates afterburner — skip if purchasing Loring S15 with factory unit.
Step 3: Calculate thermal input
Afterburner burner sized at 150,000–250,000 BTU/h for 12 kg exhaust stream. Under-sizing causes visible smoke; over-sizing wastes gas. Request burner turndown ratio ≥ 4:1 for idle periods.
Step 4: Plan electrical and gas service
Afterburner adds separate gas line (often 150,000 BTU/h) and 30–60 A three-phase electrical for ignition and fan. Combined with roaster, verify total site capacity.
Step 5: Install and compliance test
Stack test after 50-hour burn-in. US: opacity < 20% Ringelmann (where required). EU: third-party emission test per EN 13792. Archive results for permit renewal.