Range hood not pulling smoke? Diagnose weak vent hood suction
Cooking
Photo: Hồng Quang Official / Pexels A hood that runs loudly but leaves haze hanging over the range is doing almost nothing useful. Airflow problems have a short list of causes, and you can rule out most of them in an afternoon without any tools beyond a screwdriver and dish soap.
Degrease the baffle or mesh filters
Grease-saturated filters are the single biggest cause of lost suction. Baffle filters pull out and can go in the dishwasher or soak in hot water with degreaser and a scoop of baking soda for thirty minutes. Aluminum mesh filters should be hand-washed since dishwasher detergent discolors them. Do this every one to three months depending on how much you fry.
Check the damper flaps
There is a damper at the hood outlet and usually another at the exterior wall or roof cap. Grease gums them shut, and birds and insects nest behind the outside cap. With the blower off, look up into the transition and verify the flap swings freely. A stuck damper can cut airflow dramatically while the motor sounds perfectly normal.
Look at the duct run itself
Every elbow and every foot of flexible duct costs airflow. Smooth rigid metal duct moves far more air than corrugated flex. A hood rated for 600 CFM connected to a long flex run with three elbows and reduced from eight-inch to six-inch may deliver less than half its rating. Shortening the run or converting to rigid duct makes a bigger difference than a new motor.
Make-up air and tight houses
A powerful hood cannot exhaust air a sealed house will not replace. In newer tight construction, a 900 CFM hood can starve itself and even backdraft a water heater. Cracking a nearby window during heavy cooking is a quick test. If suction improves noticeably, the house needs a make-up air solution, not a hood repair.
Blower motor and speed control
If filters are clean, dampers move, and ducting is reasonable, listen to the motor. A rattling or grinding blower wheel, a motor that only works on one speed, or one that hums without spinning points to the blower motor, capacitor, or speed switch. Blower motor replacement generally runs $260 to $500 installed depending on hood type.
Hood size and mounting height
A hood should be as wide as the range and ideally three inches wider on each side, mounted 24 to 30 inches above the cooking surface for most electric ranges. A hood mounted too high loses capture regardless of CFM. Undersized over-the-range microwaves in particular struggle with a wide gas cooktop no matter how well they are maintained.
Frequently asked questions
How many CFM do I need for my range?
A common guideline is about 100 CFM per linear foot of range width for electric, and roughly one CFM per 100 BTU of total burner output for gas.
Are ductless recirculating hoods worth using?
They filter grease and odor through charcoal but remove no heat or moisture. Replace the charcoal filters every six to twelve months or performance drops off sharply.
Can I clean the blower wheel myself?
On many hoods the wheel is accessible after removing filters and a cover plate. Cut power at the breaker first, and stop if the motor must come out.