Why the Plenum Behind Your Grease Filters Needs Cleaning
Most kitchen staff know the grease filters need regular cleaning. Fewer realise there is a whole chamber behind them that collects grease as well. That space is the plenum, and it is one of the most commonly missed parts of a commercial kitchen exhaust system.
If the plenum is never cleaned, grease keeps building up just out of sight, even when the canopy and filters look spotless.
What is the plenum?
The plenum is the enclosed space between the grease filters and the start of the exhaust duct. Air drawn through the filters passes through the plenum before it travels up the duct to the exhaust fan. You only see it when the filters are taken out.
Why grease collects there
Grease filters catch a large share of airborne grease, but no filter catches all of it. Fine grease particles and vapour pass through and settle on the plenum walls, especially in high-volume kitchens or where filters are damaged, poorly fitted or overdue for cleaning.
Why it matters
- Fire load. AIRAH’s commercial kitchen exhaust guidance notes that accumulated grease can allow a kitchen fire to spread through an exhaust system. Grease in the plenum sits right above the cooking line.
- Drips. Built-up grease can drip back onto filters, the canopy or cooking surfaces.
- Airflow. Heavy deposits and grease-loaded filters can reduce how well the canopy captures smoke.
- Records. If an insurer or auditor asks what was cleaned, “the filters” is a weaker answer than a report showing the whole system.
How a professional clean handles the plenum
During a kitchen exhaust and canopy clean, filters are removed, the plenum is degreased and cleaned, and the work continues into the duct and fan where accessible. With our service, the plenum is included in the job photos and recorded in the PDF report in your service records.
What your team can do between cleans
- Keep filters on a regular cleaning or filter exchange schedule.
- Replace damaged or poorly fitting filters, since gaps let more grease through.
- Report any dripping or grease that returns quickly after cleaning.
- Do not try to clean inside the plenum yourself while equipment is hot or without safe access.
New to the terms? See our kitchen exhaust glossary. To book a full-system clean in Melbourne or Victoria, call (03) 9303 9661 or request a quote below.