Range Hood Repair
Nameplate CFM Is Not What You Get: Title 24 Ducting and Make-Up Air in Los Angeles Kitchens
Written by
Noor Haddad
Cooking-appliance technician — induction and electric · 8 years in the trade
The call we take most often here
“It runs, and the smoke still crosses the kitchen.” The hood is audible, the lights are on, nothing is broken, and the cooking surface is not being cleared. In most of these visits the equipment is performing to specification. The specification simply never described the duct it was hung on.
That gap between a rating and a result is where nearly every Wolf ventilation complaint in this part of the city actually lives.
Why this address produces it
Start with the rule, because it is unambiguous. Title 24 Part 6, Section 150.0(o) of California’s Energy Code governs every dwelling-unit kitchen in the state, additions and alterations included. An installed range hood has to be HVI- or AHAM-certified and listed in the directory; it has to deliver its required airflow at installed conditions rather than at nameplate; it must not exceed 3.0 sones at that airflow; and it has to be ducted to the exterior, which means a recirculating hood does not comply. The duct itself has to be smooth rigid metal — the California Mechanical Code prohibits flexible duct for kitchen exhaust. HVI publishes certified airflow at 0.1 inch water column, and that is the figure that matters.
None of that is a Los Angeles rule; it applies in Sacramento identically. What is local is the duct you inherit. Larchmont Village kitchens behind pre-1940 Spanish Revival and Craftsman fronts, and the post-war Mar Vista bungalows, commonly still run the original path: a 3-1/4 by 10 rectangular duct in the wall, or a 6-inch round, sized for a 1950s vent fan and never touched since. Compact original kitchens in Cheviot Hills, and Encino ranch houses reworked around a big range, land in the same place — new equipment, inherited airway.
The envelope tends not to be negotiable either. The R1 variation zones adopted in March 2017 under master Ordinance 184,802 reached nearly twenty neighbourhoods in the initial rollout, Mar Vista among them as Ordinance 184,814, and they constrain what can simply be added to a house. When the walls cannot move, the duct has to be solved where it is.
The chain, from cause to complaint
A certified rating is measured against a defined resistance. The further an installed run departs from that condition, the further delivered airflow departs from the label, and there is no adjustment on the hood that recovers it.
The departures accumulate quietly. A long horizontal run to reach the only available exterior wall. Four elbows where the drawing showed two. A transition from the hood’s round collar into a rectangular wall duct. A short length of flex somebody added to make the last connection line up, which is both a restriction and not permitted for this use. Each one is small; together they can put the hood well outside the conditions its rating describes.
Capture geometry then finishes the job. A hood hung too high above the cooking surface, or narrower than the range beneath it, loses the plume at the edges no matter how much air it moves. That is why smoke drifts sideways while the blower is plainly working.
The sone limit closes the loop in an unhelpful way. An installer trying to reach a required airflow through a restricted duct ends up specifying a hood that has to live at the top of its speed range every evening. That is the vibration, the metallic rattle at the top setting, and the bearing wear that arrives a few years early.
Ruling out the obvious first
Take the filters out and wash them. Loaded baffles alone can account for a large part of a “it stopped working” complaint, and they cost nothing to eliminate.
Then check what is actually installed. Note the hood model and confirm it against the range width beneath it and against its listing. A hood narrower than the appliance it serves will never capture properly and no repair changes that.
Then follow the duct as far as you can see it. You are looking for three specific things: any flexible section, the number of direction changes, and the point where a round collar meets a rectangular wall duct. Photograph what you find; it is the most useful evidence a technician can be handed.
Then the exterior cap and its damper, which should open fully when the blower starts and not part-way.
Only then the equipment: blower wheel loading; then the run capacitor, since a motor that hums while shifting nothing points straight at it; then the speed control. Two symptoms name themselves — a blower that keeps spinning after the switch is off is the speed control or a delay circuit rather than the motor, and buzzing or half-dead lighting is the driver or transformer rather than the lamps.
When it stops being a homeowner job
Anything inside the wall or the ceiling. Replacing a mid-century duct run with compliant smooth rigid metal, resizing a termination, or working out whether the hood you own can legally and physically serve the range you bought is a permit-and-plan-check conversation as much as a repair one, and it is worth having before money is spent on a bigger blower that the same duct will strangle.
On the equipment side the published ranges are: convection fan or motor $280 to $620, control board or touch panel $450 to $880, and a $89 diagnostic visit. Mention on (310) 742-8625 what you have already tried; it shortens the visit.
Common follow-ups
Does a recirculating hood meet code in a California kitchen?
No. Title 24 Part 6, Section 150.0(o) requires an installed range hood in a dwelling-unit kitchen to be ducted to the exterior, so a recirculating unit does not comply. It also has to be HVI- or AHAM-certified and listed in the directory, deliver its required airflow at installed conditions, and stay within 3.0 sones at that airflow. Ductless filtration also does nothing for moisture or grease-laden vapour.
Why does my hood move less air than the box says?
Because the box quotes a rating and your kitchen provides resistance. HVI publishes certified airflow at 0.1 inch water column, and a run with extra elbows, a long horizontal leg, a round-to-rectangular transition or an added flexible section pushes the installed condition well past that. The hood is not faulty; it is working against a duct the rating never contemplated, and no speed setting recovers the difference.
Can I keep the existing duct from my old Mar Vista kitchen fan?
Often not, if you are fitting a serious range hood. Post-war Mar Vista and pre-1940 Larchmont Village kitchens commonly still have the original 3-1/4 by 10 rectangular or 6-inch round path, sized for a mid-century vent fan. Kitchen exhaust also has to be smooth rigid metal under the California Mechanical Code, so any flexible section has to go. Have the run assessed before choosing the hood, not after.
