Chimney suction gone weak? What each cause actually means

When smoke starts drifting sideways instead of being pulled up, the motor is rarely the first suspect. In most kitchens the cause is something blocking the path the air has to take: loaded filters, a grease-caked blower wheel, a duct that has narrowed, or a flap that no longer opens. Motors and capacitors do fail, but they come later in the list.

Work through the causes in the order below, because that is roughly the order of how common they are, and the first three cost you nothing to check.

1. Filters loaded with grease

The most common cause by a distance. Baffle filters push air through narrow curved channels, and once those channels are coated the resistance rises sharply. Pull a filter out and look at it against the light. If the gaps look glazed or you can feel a tacky film, that alone can halve the airflow.

Wash them in hot water with dishwashing liquid and a spoon of baking soda, dry fully, refit. If suction jumps back, you have your answer and a cleaning schedule to fix.

2. Grease on the blower wheel

If clean filters made no difference, the grease has gone past them. The blower wheel sits behind the filter frame and its blades are small and closely spaced. A coating a few millimetres thick changes the blade shape enough that the wheel stops moving air properly, and the imbalance makes the unit noisier at the same time.

This needs the wheel off its shaft and cleaned by hand — not a job to attempt over a live gas hob.

3. A blocked or narrowed duct

Grease vapour condenses on the inside of the duct and hardens over the years. Aluminium flexible duct is worse than rigid PVC pipe because the corrugations trap it. In Nellore homes the outdoor end matters too: birds nest in an uncovered duct outlet, and insects and leaves collect there through the monsoon.

A tell-tale sign is a chimney that sounds completely normal but moves no air.

4. The non-return flap stuck shut

Most chimneys have a light flap at the duct outlet that stops outside air, rain and insects coming back in. Grease glues it shut, or the monsoon swells and jams it. The motor then runs against a closed door. This is a five-minute fix once someone gets to it, and a common one after the rains.

5. Wrong installation height or a duct with too many bends

If suction was never good — not weak, just never right — stop looking for a fault. A hood mounted too high above the hob loses the smoke to the room before it arrives. A duct run with three or four bends, or one that travels several metres before it exits, costs a large share of the rated airflow. Every ninety-degree bend takes a bite.

6. Motor or capacitor weakening

A tired capacitor makes the motor start slowly, run below its proper speed, or hum before picking up. Evening voltage dips, common across Nellore in summer, are hard on both. You will usually hear this rather than see it: a lower pitch, a slow spin-up, or a speed setting that no longer sounds different from the one below it.

7. The kitchen has nowhere to draw air from

A chimney can only push out as much air as the kitchen can let in. Close every window and door in a small kitchen and the unit is trying to pull a vacuum. If suction is clearly better with the window open, that is not a fault — leave a window or the door ajar while cooking.

What you can check safely

Switch the chimney off at the socket or the MCB and turn the gas off at the regulator first. Then:

• Take out the filters and check them against the light.
• Look at the underside of the hood for a brown or shiny film.
• Check the duct outlet from outside, from a safe position, for a nest or blockage.
• Note whether the noise has changed and whether the speed settings still sound different from each other.

Do not open the motor cover, and do not spray water or degreaser into the motor housing.

When to call a technician

If clean filters have not restored suction, the cause is inside — blower, duct, flap or motor — and it needs the unit opened. Our weak-suction job covers a motor check and duct clearance at ₹499. If it turns out the filters are past saving, a baffle or mesh filter swap is ₹699. Any part is charged at MRP and shown to you before it goes in.