Hood not pulling smoke?
Five questions, one plain-English answer about what's wrong.
Smoke rolling into the kitchen, grease dripping from filters, roaring fans, and slamming back doors each signal a different failure in your exhaust system. Answer five quick questions about what you're seeing and we'll tell you whether it's a cleaning issue, a fan problem, a makeup-air imbalance, or a fire code violation waiting to happen, plus the right service to book before it becomes a kitchen fire.
Hood problems look similar. The fixes are not
Smoke backing into the kitchen, grease dripping from the filters, a burning smell, weak suction, an expired tag — all of these show up as "something is wrong with my hood." But they point to different parts of the system and require different responses, some urgent and some routine. The diagnostic above identifies which one you have and routes you to the right service. Here is what each failure mode actually means.
The four ways a commercial hood system fails
Hood system failures cluster around four causes. Each one looks slightly different at the equipment, and each one has a different urgency response. Knowing which one you have before you call avoids paying for the wrong service.
NFPA 96 sets cleaning frequencies based on cooking type: quarterly for high-volume solid-fuel and wok cooking, semiannual for most standard operations. These are minimums. High-volume fryer kitchens frequently need cleaning every 6 to 8 weeks regardless of the NFPA schedule.
Filter exchange is a separate service from hood cleaning — and it needs to happen more frequently. Most commercial kitchens should exchange filters every two weeks. High-volume operations may need weekly exchange. A filter that is exchanged regularly dramatically slows grease accumulation in the duct, reducing how often full cleanings are needed.
Signs of fan trouble: unusual noise from above the ceiling during service, a noticeable drop in suction that happened recently rather than gradually, or the fan running but not pulling. A hood cleaning will not fix a fan motor problem. This requires a repair diagnosis.
The compliance issue is often administrative rather than a performance problem — the hood may be clean and functioning correctly, but if the paperwork is missing, the kitchen is exposed. Every Boh hood cleaning affixes a compliant tag and files a full service report to your account automatically.
What NFPA 96 actually requires — and what LA County enforces on top of it
NFPA 96 is the national standard for commercial kitchen ventilation maintenance. It sets minimum cleaning frequencies based on cooking type: monthly for solid-fuel cooking such as wood and charcoal, quarterly for high-volume cooking including wok stations and char broilers, semiannual for standard operations with moderate grease output, and annually for low-volume cooking such as cafés and bakeries.
These are national minimums. LA County Environmental Health and the Los Angeles Fire Department both enforce NFPA 96 compliance as a condition of operation — and they have authority to cite violations and require corrective action during routine inspections. A hood cleaning tag that has lapsed, or a duct system with visible grease accumulation, is a citable violation under both authorities.
The documentation requirement is specific: inspectors want to see a dated tag affixed to the hood after each cleaning, signed by a certified technician, along with a service report on file that documents the scope of work. A receipt from a vendor is not sufficient. Every Boh hood cleaning produces both — the tag is affixed on-site and the service report is filed to your account before the technician leaves.
Cities with independent fire departments — including Long Beach, Pasadena, Glendale, Burbank, Santa Monica, Torrance, Inglewood, Beverly Hills, Hawthorne, and Pomona — enforce their own fire code compliance programs. The compliance authority is not interchangeable between cities. Boh routes to the right certified provider for the jurisdiction of your kitchen.
How often should a restaurant clean its hood system
The honest answer is: more often than the minimum, and more often than most operators are currently doing.
NFPA 96 sets the floor. Your cooking volume, menu, and equipment set the real interval. A high-volume kitchen running multiple fryers and a char broiler six days a week generates grease accumulation at a rate that a semiannual schedule cannot keep up with. Stretching the interval saves money on cleaning visits and costs it back on emergency calls, citation responses, and — in the worst case — fire damage.
The filter exchange schedule and the full cleaning schedule are separate questions. Filters should be exchanged every one to two weeks regardless of the full cleaning interval. Filters that are exchanged regularly slow duct accumulation, which means full cleanings can be spaced further apart without increasing fire risk. Treating filter exchange as optional and then cleaning quarterly is the pattern most likely to produce a fire code violation.
A practical rule for Southern California restaurant operators: if your hood produces visible grease on the baffle filters within two weeks of a full cleaning, you are either exchanging filters too infrequently or your full cleaning interval is too long for your cooking volume. Boh can advise on the right schedule based on your kitchen output after the first service visit.
Common questions
What is the difference between a hood cleaning and a filter exchange?
Hood cleaning is a full service of the entire exhaust system — hood interior, ducts, exhaust fan, and all accessible surfaces — performed by a certified technician to NFPA 96 standard. It happens quarterly or semiannually depending on cooking volume. Filter exchange is the routine swap of baffle filters every one to two weeks — dirty filters out, clean ones in. The two services address different parts of the system and both are necessary. Doing one does not replace the other.
My hood was cleaned three months ago but there is grease dripping from the filters. Does that mean the cleaning was done wrong?
Not necessarily. Visible grease on or dripping from baffle filters between full cleanings almost always means the filter exchange interval is too long for the cooking volume. Filters that are not exchanged frequently enough saturate and allow grease to pool in the drip trough. The full cleaning may have been performed correctly — the gap is in the weekly filter maintenance, not the quarterly service.
Do I need a hood cleaning if I only have a light-cooking menu?
Even low-grease cooking environments accumulate grease in the duct over time, and NFPA 96 still requires annual cleaning for low-volume operations. The more relevant question is whether your current interval matches your actual cooking output. If your menu has changed — more frying, more volume, a new char broiler — and your cleaning schedule has not, you are likely under-cleaning relative to what the hood is processing.
My suppression system went off. Do I need a hood cleaning before I can reopen?
Yes. After a suppression system discharge, the hood, duct, and suppression system all need to be serviced and re-certified before the kitchen can resume operation. The suppression system must be recharged and re-tagged. The hood and duct need to be cleaned — the discharge agent leaves a residue that must be removed. LA County will require documentation of both before permitting reopening. Boh can dispatch both services and coordinate the timing.
What happens if I get a grease violation during a health inspection?
LA County issues a major violation for visible grease accumulation on hood surfaces, filters, or ducts. The violation requires documented corrective action — a professional cleaning with a service report — before a re-inspection. The re-inspection must occur within the timeframe the inspector specifies. Failing the re-inspection can result in a grade downgrade or a conditional permit that puts your operation at risk. Boh can dispatch a certified technician for a same-day or next-day cleaning with full documentation to present at re-inspection.
How do I know if my exhaust fan needs repair rather than just a cleaning?
The key signal is whether the performance change was sudden or gradual. Grease accumulation causes a slow, progressive reduction in suction over weeks or months. A fan motor or belt problem tends to produce a noticeable drop that happens over days — along with unusual sounds from above the ceiling. If suction dropped suddenly and you can hear noise from the fan housing, the issue is mechanical. If suction has been gradually declining and the filters are saturated, the issue is grease. The diagnostic tool above helps distinguish between the two.