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Before and after pictures of commercial kitchen hood in North Bay, Ontario.
Before and after pictures of commercial kitchen hood in North Bay, Ontario.

Kitchen exhaust cleaning (often referred to as hood cleaning) is the process of removing grease that has accumulated inside the ducts, hoods, fans and vents of exhaust systems of commercial kitchens. Left uncleaned, kitchen exhaust systems eventually accumulate enough grease to become extreme fire hazards.[1][2] Exhaust systems must be inspected regularly, at intervals consistent with usage, to determine whether cleaning is needed before a dangerous amount of grease has accumulated.

Cleaning processes

The exhaust system is first scraped clean; sometimes scraping isn't necessary if the grease exhaust system has been maintained properly chemical and hot water, then washed clean with food-safe caustic chemicals and hot water pressure-washing where possible to safely collect the dissolved grease and water. The actual commercial kitchen exhaust system cleaning guidelines are outlined in the National Fire Protection Association (NFPA). The cleaning frequency depends on the type of food being cooked and volume of grease laden vapors drawn up through hood plenum. For example, one church may require less servicing because they use the system 10 times a year, while another church would require more frequent attention because they have a weekly Friday night fish fry. Typical cleaning intervals are monthly, every two months, quarterly, semiannually and annual.

Caustic chemicals

Caustic chemicals can be applied to break down the grease. After that, hot water can be used to rinse away the residue. Chemicals are generally applied with either a garden-type sprayer, downstream injection through a pressure washer or with a chemical foamer.[3]

Once the chemicals are applied, they are allowed to dwell on the surface of the grease for a period of time, before being washed off of the surface with hot water. In extreme situations, where grease buildup is too heavy for a chemical application and a rinse, scrapers may be used to remove excess buildup from the contaminated surfaces, before chemicals are applied.[4]

Hot water pressure-washing

Machines can be used that both boil water and then apply this water under pressures up to 2,000 pounds per square inch (14,000 kPa). In a common method of preparation, heavy-duty tarps are first clipped to the hoods and then angled into plastic garbage cans to catch the run-off. As the cans are filled the contents are disposed of successively. The grease should be removed rather than just emptied into the local drains to avoid clogging. Some problems that can arise from improper horizontal duct cleaning include excessive grease buildup up in inaccessible ductwork. Steam cleaners tend to move the grease further in to the grease duct work, which can cause massive grease accumulations in areas of the duct work between the hood and fan on the roof. Companies using hot water methods should be using a caustic chemical degreaser to break down grease, so that the build up in inaccessible areas becomes removed by flushing the system with both hot water and caustic degreaser agents.


Cleaners often polish hoods for easier cleaning and improved appearance. Cleaners apply a certification sticker to the hood of each cleaned kitchen exhaust system to enable the authority having jurisdiction as well as insurance adjusters and health inspectors to check for compliance with the local, county and state fire codes. Vinegar and warm water can be used to remove any white residue left from the commercial kitchen grease cleaning process.


Many jurisdictions have adopted this nations minimum available standard, National Fire Protection Association Standard 96, Standard for Ventilation Control and Fire Protection of Commercial Cooking Operations,[5][6] and require compliance to it by Kitchen Exhaust Hood Cleaners and operators of commercial kitchens.

Industry education

A properly cleaned kitchen exhaust duct.
A properly cleaned kitchen exhaust duct.

Several associations have been formed to educate kitchen exhaust cleaners on the provisions of NFPA 96 standard and on the best standards and practices for kitchen exhaust cleaning. Among these are:


  1. ^ "Boston fire's fuel apparently missed". 2007-09-07. Retrieved 2013-12-01.
  2. ^ "3D FIREFIGHTING - LATEST NEWS". 2007-08-29. Archived from the original on 2014-04-06. Retrieved 2013-12-01.
  3. ^ "Cleaning to a higher standard". IKECA. 2013-10-03. Retrieved 2013-12-01.
  4. ^ "Cleaning to a higher standard". IKECA. 2013-10-03. Retrieved 2013-12-01.
  5. ^ "NFPA 96: Standard for Ventilation Control and Fire Protection of Commercial Cooking Operations: About the Codes". Retrieved 2013-12-01.
  6. ^ "NFPA 96: Standard for Ventilation Control and Fire Protection of Commercial Cooking Operations". Retrieved 2013-12-01.