The most common ventilation complaint we take is some version of “it runs but it does not pull”. The blower is audible, the lights work, and a tissue held at the edge of the hood barely moves.
In an older Mandarin kitchen the blower is rarely the reason. Air has to leave the building, and the path it takes decides how much of the appliance’s rating you actually get.
What takes airflow away
These are cumulative, and in a kitchen where the hood was upgraded but the duct was not, most of them are present at once.
Diameter. A duct narrower than the hood outlet is a restriction from the first inch. Reducing to fit an existing hole in a soffit is the single most common compromise made during a kitchen renovation, because the alternative is opening the ceiling.
Flexible duct. Corrugated flex has far more internal resistance than smooth-wall metal at the same nominal diameter, and it sags between supports, which adds more. It also traps grease in every corrugation.
Elbows. Every ninety-degree turn costs airflow. A run with three of them in it is not the same as a straight run of the same length, and older kitchens with a soffit route rarely go anywhere in a straight line.
Length. Horizontal runs to an exterior wall on a larger lot — common out toward Loretto — add resistance the whole way.
Crush damage. A duct pushed through a soffit or between joists during construction is often flattened somewhere along its length. You cannot see it and it never gets better.
The termination. A wall cap or roof cap with a screen fills with grease and lint. It is outside, nobody looks at it, and it can halve the effective airflow on its own. It is also the cheapest thing on this list to fix.
Make-up air
The other half of the problem is that a hood cannot exhaust air the house has no way to replace.
A high-capacity hood moves a serious volume of air, and many jurisdictions require a make-up air provision above a certain airflow for exactly that reason. Where none exists, one of two things happens.
In a tightly built house the hood stalls against its own vacuum: the blower turns at full speed, the pressure difference climbs, and the actual flow collapses. In a leakier older house — most of Mandarin’s 1970s stock — the replacement air arrives down whatever else is open, which can mean pulling air backwards down a water heater or fireplace flue. That is a safety matter, not a performance one.
A simple test: crack a window in the kitchen and run the hood again. If it suddenly performs, the house was the restriction.
What we can and cannot do about it
We diagnose and repair the appliance. We can tell you what the duct is doing, what the termination looks like, and whether the hood is being defeated by the building. We can replace blower motors, wheels, dampers, switches and lamp holders, and we can service filters and correct their seating.
We do not run new ductwork or install make-up air systems. What we will do is describe honestly, in the written estimate, what is appliance and what is house — because a new blower motor fitted to a duct problem is money spent to change nothing.
One boundary worth drawing hard, because this page is full of the word duct. The duct written about here is kitchen exhaust: a run from the hood, through a soffit or a roof, carrying grease and steam out of the house. It is not the duct that carries conditioned air around it. Heating and air conditioning — furnaces, heat pumps, air handlers, mini-splits and their ductwork — are a separate trade with a separate licence, and none of it is work this shop takes on or quotes for. If the room is the wrong temperature rather than the hood the wrong performer, the call you want is an HVAC contractor’s.
The things that are the appliance
Not every complaint is the duct, and these are worth knowing.
A hood that has become much louder at the same setting usually has grease built up unevenly on the blower wheel, which puts it out of balance. That noise climbs for months before anything fails.
A blower that hums but does not turn is generally seized rather than dead — a motor that sat through a humid summer, or a wheel jammed with hardened grease.
Speed settings that fail one at a time point at the switch, not the motor. Lamp positions that flicker are usually corroded or loose holders rather than failing lamps.
Air blowing down through the hood on a windy day is the backdraft damper not closing: a flap fouled with grease, a lost counterweight, or a stuck damper at the wall cap. Small part, large comfort effect, and in this climate it also lets humid outside air into a conditioned kitchen all summer.
Filters
Baffle filters work by forcing air to change direction sharply so grease is thrown out of the stream. They only do that when they are clean and correctly seated. A wash every few weeks keeps them working. A set that has not been washed in a year is both a performance problem and a fire load sitting directly above a professional range.