Chimney Suction Power Explained: How Much m³/hr Do You Need?

Chimney suction power is measured in cubic metres of air moved per hour (m³/hr). To find what you need, multiply your kitchen’s volume in cubic metres by ten. For most Kolkata kitchens that lands between 1200 and 1500 m³/hr. But the number on the box is a laboratory figure — what you actually get depends heavily on how the chimney is installed.

Key takeaways

• m³/hr = cubic metres of air the chimney can move per hour.
• Rule of thumb: kitchen volume (m³) × 10 = minimum suction needed.
• Indian cooking needs more than European guidance suggests — add headroom.
• Rated figures are measured with no ducting. Every bend costs you real airflow.
• A clogged filter can cut effective suction more than choosing a lower-rated model would.

What the number actually means

A chimney rated 1200 m³/hr can, under test conditions, move 1200 cubic metres of air through itself in an hour. Since a typical Kolkata kitchen holds somewhere around 20–30 cubic metres of air, that rating implies the chimney could exchange the room’s entire air volume roughly 40–60 times an hour.

That sounds like enormous headroom — and it is, in the laboratory. Real installations do not achieve it, which is why the rest of this article matters more than the rating.

How to calculate what you need

1. Measure your kitchen — length × width × height, in metres. A 3m × 2.5m kitchen with a 3m ceiling is 22.5 m³.
2. Multiply by 10 for a baseline: 225 m³/hr — but that is the bare minimum air-change figure, not a purchase spec.
3. Apply the cooking multiplier. Indian cooking, especially frying and tempering, needs substantially more than the baseline. In practice this puts most kitchens in the 1200–1500 m³/hr band.
4. Add headroom if the kitchen is enclosed, has one small window, or opens onto a living area.

Why the rated figure is not what you get

This is the part manufacturers do not advertise, and it is the most useful thing on this page.

Rated suction is measured with the motor running free — no ducting attached, no filter loaded, no back-pressure. Your installed chimney has all three.

Duct length and bends. Every bend forces air to change direction, and each change costs airflow. A duct with three or four turns can lose a substantial fraction of the rated figure. A short, straight run keeps far more of it. This is why a well-installed 1200 m³/hr unit routinely outperforms a badly ducted 1500.

Duct diameter. Narrowing the duct below the chimney’s outlet size throttles it. If an installer reduces the diameter to fit an existing hole, you lose performance permanently.

Filter loading. A grease-saturated filter is a restriction. This is the biggest variable of all over time, and entirely within your control.

The practical conclusion: installation quality and maintenance affect real suction more than the difference between two adjacent model ratings.

Suction is not the only thing that captures smoke

Two other factors decide whether smoke actually reaches the chimney.

Width. A chimney narrower than the hob lets smoke escape past both ends no matter how strong the motor is. Match or exceed the cooktop — 90cm for three or four burners.

Mounting height. Roughly 65–75 cm above a gas hob. Mounted higher for headroom, smoke disperses before it is captured. This is one of the most common reasons a correctly specified chimney underperforms.

Keeping the suction you paid for

In Kolkata this needs more attention than elsewhere. The long humid season keeps deposited oil tacky rather than letting it dry and flake off, so grease and dust build a restrictive layer faster than the generic service interval assumes.

Clean or replace filters on schedule, and book a professional deep clean yearly to clear the blower housing and duct — the parts you cannot reach. A chimney run choked makes its motor work against back-pressure, which is the usual path to premature failure.

Written by RS, RS Appliances / GITA, the authorised Kutchina dealer and service partner in Kolkata.