Kiln Vent

What it is

Firing clay and glaze releases gases that you do not want in the room. Organic matter in the clay burns off as carbon monoxide and smoke. Sulphur compounds come out of the body. Metal oxides and fluxes in the glaze vaporise. At cone 6 and above, lead-free does not mean fume-free — there are still volatile compounds in the exhaust.

A downdraft vent is the standard solution. A small fan pulls air from the room, through the kiln chamber via a slotted manifold under the floor, and out through a duct to the outside. Because the chamber is under slight negative pressure, fumes travel out rather than leaking into the room. The side benefit is more even firings and better glaze colour, since oxygen circulates through the load.

An overhead hood with a fan is the alternative, and it is cheaper but less effective: it captures fumes as they rise out of the kiln rather than preventing their escape. For any kiln indoors, the downdraft vent is the better choice. It should be ducted to the outdoors with metal ducting, and the exhaust point must be away from windows and air intakes.

How to use it well

• Run the vent for the entire firing plus 30 minutes of cooling, not just the peak.
• Inspect the manifold slots and duct annually for dust and blockage.
• Keep the duct run short and straight — long runs with bends lose most of the airflow.
• Log the vent running alongside the firing schedule so you can spot a failed fan early.

Safety notes

• Firing without ventilation in an enclosed space can produce dangerous carbon monoxide. Never rely on an open window alone.
• Duct the exhaust outside, away from windows, doors and air intakes.
• Fit a carbon monoxide alarm in any room containing a kiln.
• Check the fan runs whenever the kiln is on — a failed fan is an invisible hazard.

Compatible materials

Clay bodies

• All bodies

Glazes & surface

• All glazes — especially those with metal oxides

Where it sits in the process

Bisque, glaze and specialty firings in the kiln.

Firing  Kiln & Firing  Pro tier

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