A Hood That Moves Less Air Than It Should

A hood that has quietly weakened over two or three seasons is one of the most frequently misdiagnosed appliances in the kitchen. The motor still runs, so the owner concludes it is tired and asks for a new one. Replacing it usually changes very little, because the resistance the old motor was fighting is still there.

Extraction is a system property. The fan is one component of it.

The four places airflow actually goes

Filters. Baffle filters work by forcing greasy air to change direction sharply so the grease separates out. As grease polymerises inside the baffles, those channels narrow. Airflow falls off well before the filters look convincingly dirty, which is why people are surprised when a dishwasher cycle restores half the performance. Run them through on a regular schedule and a hood will hold its rated performance for years.

The duct run. Every elbow and every foot of horizontal run costs pressure. A hood that was correctly specified at installation can become undersized after a remodel that added two bends to get around a new soffit, or that reduced the duct diameter at a transition to fit a joist bay. We measure the actual run rather than assuming the original one is still there.

The termination. The cap on the roof or the wall is where the appliance meets the weather, and it is the component most likely to have been forgotten. A damper flap that has corroded part-open, screening blocked with debris, or a bird screen doing its job thoroughly will throttle a perfectly healthy blower. On the lakefront elevations along Doctors Lake this is the first thing we inspect, because those terminations take wind-driven rain and constant damp and their moving parts seize.

Make-up air. A professional hood moves a serious volume of air out of the house, and the same volume has to come back in from somewhere. In a tightly built house — and most of Oakleaf Plantation is tightly built — there may be no adequate path. The hood then pulls against the building envelope rather than through it. The signs are recognisable: doors that resist opening while the hood is on high, a hood that is loud but ineffective, and, most importantly, any change in the behaviour of a gas appliance elsewhere in the house when the hood goes to full speed.

That last symptom is a safety matter and not a comfort one. If you can hear or see a combustion appliance change when the hood goes to high, stop using the high setting until the make-up air path has been looked at properly. We will document what we find in writing whether or not the remedy is something we can supply.

When it is the blower after all

Blowers do fail, and the pattern is usually legible before anything is disassembled.

Running on one speed only points at the speed control or the switch, not the motor. Humming without starting points at a capacitor or a seized bearing. A new rattle at high speed, after years of quiet running, is normally a wheel that has loaded unevenly with grease or a mount that has worked loose — and it deserves prompt attention, because an out-of-balance wheel destroys its own bearings.

Configuration matters here. When the blower is mounted remotely — in the attic or on an exterior wall rather than inside the canopy — everything at the canopy can test correctly while the fault sits thirty feet away. Telling us which arrangement you have when you book genuinely saves an hour.

What is not the cause

The motor, most of the time. What accumulates in a hood is grease, and it loads the baffles, the canopy, the blower wheel and the first few feet of duct in roughly that order. Every one of those raises resistance without touching the motor at all, and every one of them responds to cleaning rather than to parts.

There is a second non-cause worth naming: the hood’s rated airflow. A figure on a specification sheet is measured on a test rig with a short straight duct, not on your roofline with four elbows and a damper in the way. A hood that has never extracted well in a particular kitchen is usually describing its installation rather than a defect, and the fix is in the duct rather than in the canopy.

Terms

Flat $129 diagnostic, credited toward the repair when you approve the work. A written estimate before any part is ordered. Genuine OEM parts, 90 days on labour and 365 days on parts.