Most restaurants have their kitchen exhaust systems "Hoods" cleaned every 3, 6 or 12 months per NFPA 96 fire code to remove the grease from the system. Cleaning per NFPA 96 requires the system to be cleaned from top to bottom. That means, from the fan on the roof or side of building, the ducts that lead to the hood and the hood itself.
Following the completion of the job, your cleaning company will issue a certification of services performed by placing a service sticker on your hood with when the service will expire.
It is not standard for professional exhaust cleaning companies to include cleaning your filters on-site as part of the service, however, they are required to be cleaned per NFPA 96, 12.6.2 Hoods, grease removal devises.....shall be cleaned to remove combustible contaminants prior to surfaces becoming heavily contaminated with grease or oily sludge.
But why should we need filters exchanged/cleaned more regularly if our hood cleaners have been doing this for years?
Grease filters are made to capture between 35%-98% of the effluent that goes up toward the duct and fan. In order to keep them functioning properly, you need to avoid them becoming heavily soiled, they need regular cleaning.
Captive-Aire and Greenheck hoods post in their manuals recommended cleaning frequencies based on cooking type, but regardless, if you are cleaning your filters in-house, they need to be cleaned the proper way at least 1x per week. Grease filters are harder to clean the longer in between cleaning sessions because they are subjected to constant heat, continued accumulation and baffles that allow the grease to hide from the un-trained eye.
If you are using a Filter Exchange Company, you can often go longer between cleaning because the system they use to clean the filters will allow for 99%-100% cleaning even on fairly dirty filters.
The responsibility, per the fire code, falls on the owner/tenant to ensure the fire-readiness of those filters.