Hood airflow and makeup air

A hood that does not clear steam is usually not a broken hood. It is a hood attached to a duct that cannot carry what the blower can move, or installed in a house that cannot supply the air the blower is trying to remove. Both problems look identical from the kitchen, and neither is fixed by a new motor.

A fan can only move air that can get in

This is the part that surprises people. Exhaust is not a one-way process — for every cubic foot the hood pushes out of the house, one cubic foot must come in from somewhere. In a leaky old building it arrives through the building itself and nobody notices. In a tight modern envelope there is nowhere for it to come from, and the fan simply stalls against the pressure it has created.

Nocatee houses were built from 2007 onward to a considerably tighter standard than the 1920s stock in the historic Duval neighbourhoods. That is excellent for cooling bills and it is precisely what makes powerful kitchen ventilation require planning here.

The symptoms of a house with no makeup air path are recognisable:

• Exterior doors are noticeably harder to pull open while the hood is on high
• A whistle or draught at a closed window or a door frame
• The hood works visibly better with a window cracked
• The dryer or a combustion appliance struggles to vent
• The hood is quiet and moving nothing, rather than loud and moving nothing

Widely adopted residential mechanical code requires a makeup air path once exhaust capacity exceeds 400 cfm, and professional hoods routinely exceed that figure on their top speed. If your house shows the symptoms above, this is a building question for a licensed mechanical contractor, not a repair. We will identify it and tell you, because selling you a blower for it would be selling you nothing.

The duct is half the system

Manufacturer airflow figures are measured on a test rig, not on your duct run. What your hood actually delivers depends on the path.

Diameter. Airflow resistance rises sharply as duct diameter falls. A blower sized for a large-diameter duct loses a great deal of its capacity through a transition that necks the run down — which happens routinely when a bigger hood is fitted to an existing duct.

Material. Flexible duct has several times the resistance of smooth-wall rigid duct of the same diameter, and a flex run that sags between joists is worse than that. If a hood has never performed since move-in, look here first.

Length and elbows. Every foot of duct and every change of direction adds resistance. Two ninety-degree elbows close together cost far more than the same two elbows separated by a straight section.

Termination. The cap at the roof or wall has a backdraft damper. Grease stiffens it, exterior paint seizes it, and a damper that does not open fully throttles the whole system.

What we can actually service

The hood itself is straightforward. Baffle filters go through the dishwasher on a four-week cycle in a household that cooks most nights, and a loaded set is frequently most of an airflow complaint on its own. Blowers that have changed pitch usually have a bearing going or a wheel unbalanced by accumulated grease, and cleaning and rebalancing the wheel is often enough. Speed faults split cleanly: one speed working and the others not points at the switch or the speed board, and nothing working at any speed points at the supply. Canopy lighting is generally a low-voltage circuit with a driver, so a whole side going dark is a driver or a connector rather than lamps.

What we will not do is replace a working component to compensate for a duct or a building. That is the whole point of measuring before quoting.

Salt air is not a factor at this ZIP

Corrosion of hood hardware, fasteners and exterior caps is a genuine issue on the coastal ZIPs — 32082, 32250, 32266, 32233 and 32084 among them. Nocatee’s 32081 is not one of them. Hardware here corrodes at ordinary inland rates, and we do not bill time looking for a problem the geography does not produce.