Chimney installation: height above the hob, duct length and bends

A kitchen chimney's performance is decided at installation, not at the shop. The same unit that clears a kadai of smoke instantly in one kitchen will look useless in another, and the difference is almost always height above the hob, duct diameter, run length and the number of bends. If a chimney disappointed you from the first week, it was installed wrong, not sold wrong.

The three numbers worth knowing: mount the hood roughly 60 to 75 cm above the cooktop, keep the duct as close to a straight three-metre run as the kitchen allows, and never reduce the duct diameter below what the chimney's outlet was designed for.

Height above the hob

Too high and the smoke plume spreads and cools before it reaches the hood — you see it drift sideways past the edges. Too low and you cannot get a tall vessel onto the back burner, and the hood picks up heat that shortens the life of the electronics.

Set it for the person who cooks most. A shorter cook is better served nearer 60 cm; a taller one nearer 75. If a wide kadai is in daily use, check the clearance with that kadai on the burner before the bracket goes on the wall.

The hood should also cover the burners, not sit behind them. A 60 cm chimney over a wide four-burner hob will always miss the outer burners; a 90 cm hood is the usual answer.

Duct diameter, length and bends

The duct is where most of the rated suction quietly disappears.

• Diameter. Use the size the chimney outlet is built for, usually 150 mm. Squeezing it down to fit an existing hole in the wall throttles the whole unit permanently.
• Length. Under three metres is comfortable. Beyond that the losses add up and grease has more surface to settle on.
• Bends. Each ninety-degree bend costs a meaningful share of the airflow. One is normal, two is acceptable, three is a problem. Two gentle 45-degree turns beat one sharp right angle.
• Material. Rigid PVC or a smooth-walled duct outperforms corrugated aluminium flexi duct, which is both more restrictive and much better at trapping grease in its ridges.
• Slope. A slight downward slope towards the outside end means condensed oil and monsoon water drain out, not back into the motor.

The outside end

This matters more in Nellore than people expect. The duct outlet needs a cowl or a non-return flap. Without one, north-east monsoon rain drives straight in, birds nest in the pipe during the dry months, and insects collect in it. A blocked outlet makes a healthy chimney behave like a dead one.

On the coastal side of the district, salt air corrodes exposed clamps and screws faster. Ask for stainless fixings where they are visible outside, and check that spot at service time.

Power point and clearances

The chimney needs its own switched socket, ideally behind or beside the hood rather than directly above the burners, and it should be reachable so you can switch off before cleaning. Keep the LPG hose or pipeline run away from the chimney body and from the socket — the hose should never touch a hot surface or sit where oil drips onto it.

Leave enough clearance from adjacent cabinets that the hood can be taken down for service without dismantling the modular kitchen around it.

What good installation looks like on the day

• Bracket fixed into solid wall with the right anchors, not into a hollow panel alone.
• Hood level, checked with a spirit level, so oil runs to the collector cup and not to one corner.
• Duct joints clamped and sealed with proper tape, no loose sleeve.
• Duct sloping slightly outward, cowl or flap fitted at the wall.
• Unit run at full speed at the end and tested with a paper napkin held against the filter face.
• Old unit, if any, taken down and the old wall hole capped so it does not become an insect route.

Our installation job — chimney mount, duct run and power — is ₹799, and taking down an existing unit with the duct capped off is ₹399. Ducting material and any part are charged at MRP and shown to you before the work starts.

If it is already installed badly

Height can usually be corrected. A duct run with too many bends can sometimes be shortened, sometimes not, depending on where the outside wall is. It is worth having someone look before you conclude the chimney itself is weak — replacing a unit that was only ever fighting its own ducting changes nothing.