ACHR News covered HEMCO's Corner Canopy Hood, a laboratory product that fits into a corner. The outlet describes it as "a compact option for capturing corrosive vapors, heat, steam, and odors." You will not be installing a lab canopy over your range, but it describes the same job your kitchen hood has. A hood works only when it catches the plume at the source, moves it through a duct that passes air freely, and gets replacement air to replace what it removes. Each of those conditions can be measured before you buy a new fan or blame the appliance.
Start With the Smoke Test
Light an incense stick or hold a strip of thin tissue at the front edge of the hood, then run the fan on high. Watch the path. Smoke should bend into the hood face and disappear into it. If it drifts past the sides, rolls off the front toward your face, or hangs over the cooktop, the hood is not capturing the plume. Check the mounting height next. Many hoods sit higher than the manufacturer's spec, and a hood mounted high pulls less from the pan. Find the height on the spec sheet, then measure from the cooking surface to the bottom edge of the hood.
Measure the Pull, Then Read the Rating
A vane anemometer held across the filter face gives a usable airflow number. Take readings at several points across the face, average them, and compare the result to the fan's rated airflow on the nameplate or spec sheet. A reading well below rating means something is restricting flow. The restriction usually sits in one of three places: the filter, the duct, or the outdoor termination. Take the readings with a clean filter so you know whether cleaning restores capacity or whether the problem is further down the line.
Trace the Duct
Follow the duct from the hood to the exterior. Count the elbows, note every horizontal run, and check whether flexible duct sags or gets crushed in a joist bay. Each elbow and each stretch of flex adds resistance. A short, straight metal run to an exterior cap moves air far better than a long, crooked run ending in a plastic cap. Go outside and look at the damper while someone runs the fan. The flap should lift freely and close fully when the fan stops. A stuck flapper feels like a weak fan from inside the kitchen, and it is easy to mistake for a motor problem.
Check the Replacement Air
A hood that exhausts hard in a tight house pulls air from wherever it can find it. Close the kitchen door, run the hood on high, and check for a draft at the nearest door gap or return grille. Listen for the change in room pressure when the hood starts. If another exhaust fan, such as a bath fan, runs at the same time, the house pulls harder. If a gas water heater, furnace, or fireplace flue backdrafts when the hood runs, stop running that combination and have a qualified technician evaluate the venting before you use it again. Replacement air is a building question as much as a fan question, and a dedicated intake may be the real fix.
Run It the Way a Lab Would
Lab hoods capture at the source, which is why they sit close to the process instead of across the room. Your version is simple. Turn the hood on before the pan heats, keep the heaviest steam on the front burners where the hood face can reach it, and leave the fan running for a few minutes after cooking so residual heat and odor clear. Clean the filter on a schedule you can name out loud. Grease loading narrows the path through the filter, and a loaded filter quietly cuts the pull you just measured. If the filter is a baffle type, wash it in hot water with a degreaser. If it is a mesh type, check that it still seats tightly in its frame, because a gap there lets air bypass the filter altogether.
Keep the Numbers
Write down the date, the fan speed, the anemometer average, the filter condition, and the result of the smoke test. Repeat the same tests after a filter cleaning, a duct change, or a fan replacement. Without a baseline, you cannot tell whether the hood got weaker or your memory did. A simple log on the inside of a cabinet door is enough, and it turns the next service call from a guess into a comparison.