Before and After Hood Cleaning: What Professional Service Looks Like

If you have never had your commercial kitchen hood professionally cleaned — or if you suspect your current provider is cutting corners — understanding what a proper cleaning looks like will help you evaluate the job. This article walks through the full process from initial assessment to final documentation.

What You Are Looking At: Before the Cleaning

A commercial kitchen exhaust system that is due for cleaning shows several telltale signs. Knowing what to look for helps you understand why professional cleaning is necessary and why your staff’s filter washing is not a substitute for the real thing.

The Hood Interior (Plenum)

Behind the grease filters, the hood’s interior chamber — called the plenum — collects grease-laden vapors that pass through the filters. Before cleaning, you will typically see:

• A thick layer of brown, yellow, or black grease coating the interior walls
• Grease dripping downward and collecting in the trough or drain at the bottom
• In severe cases, grease deposits thick enough to change the airflow characteristics of the hood
• Discoloration and staining on stainless steel surfaces

This is the area most people never see because it is behind the filters. It is also where a significant fire hazard develops — accumulated grease in the plenum is fuel for a fire.

Grease Filters

Even when staff clean filters weekly (as they should), there is always some residual grease. Before a professional cleaning:

• Filters may have a visible grease glaze even after staff cleaning
• Mesh or baffle openings may be partially clogged, reducing airflow
• In neglected kitchens, filters can be so loaded with grease they are nearly opaque

Ductwork

You cannot see inside the ductwork without opening access panels, but a professional cleaning company will. Before cleaning:

• Duct interiors have a coating of condensed grease, ranging from a thin film (well-maintained kitchens) to thick, tarry deposits (neglected systems)
• Horizontal runs and elbows accumulate the most grease because gravity causes it to settle
• In extreme cases, grease deposits can narrow the duct’s effective diameter, reducing airflow

Rooftop Fan

The exhaust fan on the roof pulls air through the entire system. Before cleaning:

• Fan blades are coated in grease, reducing efficiency and increasing motor strain
• The fan housing has grease pooling in the bottom
• The grease drain or catch pan may be overflowing
• Grease may be leaking onto the roof surface around the fan base

The Professional Cleaning Process

Here is what happens during a proper hood cleaning, step by step:

Step 1: Assessment and Setup

The crew arrives (typically during off-hours, between 10 PM and 6 AM) and begins with:

• Initial inspection: Walking through the kitchen, examining the hood, removing filters to look at the plenum, noting system condition
• Before photos: Timestamped photos of the hood interior, filters, accessible ductwork, and fan — these become part of your compliance record
• Kitchen protection: Covering all cooking equipment, food prep surfaces, and the floor with plastic sheeting. The cleaning process involves chemicals and water, so protecting the kitchen is essential
• Electrical and gas safety: Turning off cooking equipment and verifying the system is safe to work on

Step 2: Filter Removal and Cleaning

All grease filters are removed from the hood:

• Filters are soaked in a hot degreasing solution
• Heavily soiled filters are scrubbed with specialized brushes
• Filters are rinsed thoroughly and inspected for damage
• Damaged filters are noted in the technician report — warped or broken filters need replacement

Step 3: Hood Interior Cleaning

This is the core of the job. The hood interior (plenum) is cleaned using a chemical-first approach:

• Chemical application — dirtiest areas first: Industrial-strength degreaser is sprayed on the heaviest grease buildup before anything else. Corners, seams, and the worst spots get chemical first so it has maximum dwell time on the toughest grease. The technician works methodically — by the time they finish spraying the full hood, the first areas are already breaking down
• Monitoring during dwell: While chemical sits, the crew watches the protective plastic over your equipment for bubbling or displacement, and avoids saturating fire suppression components
• Pressure washing: High-pressure hot water removes the chemical and dissolved grease. One pass usually knocks off the majority of buildup. Heavily soiled areas get additional passes
• Water containment: All dirty water is captured in containers and monitored throughout — when they fill up, the crew drains them into the mop sink (or a customer-specified location). Off-site water transport is available for an additional fee
• Dry and shine: After washing, the crew squeegees excess water off every surface, then hand-dries with clean towels using a mop stick to reach every area. Once completely dry — this step cannot be rushed, because any remaining moisture causes streaking — a professional stainless steel finish is applied with fresh towels. This finish acts like a wax, giving the hood a uniform polished look. New towels are used for every hood to prevent cross-contamination

The goal is bare metal with a professional shine. After proper cleaning, you should see the stainless steel surface with no grease film, and the hood should look better than the day it was installed.

Step 4: Ductwork Cleaning

Ductwork cleaning works from both access panels and from below through the hood opening:

• Access panels are opened at each point (every change of direction and at regular intervals)
• Chemical degreaser is applied inside the duct
• The technician works the pressure wand up into the duct and sprays each side individually — this is physically demanding work, but it is the only way to clean duct interiors thoroughly from below
• The crew works systematically from the hood to the fan, ensuring no section is missed
• Long horizontal runs require the most attention — gravity causes grease to settle and accumulate here

If your ductwork does not have adequate access panels, a thorough cleaning is difficult or impossible. This is a common issue in older NYC buildings and should be corrected. Your cleaning company should note any access deficiencies in their report.

Step 5: Fan Cleaning

The rooftop fan is cleaned last:

• The fan housing is opened (hinged fan assembly tilted up)
• Fan blades and housing interior are scraped and degreased
• The catch pan or drain is cleaned
• The fan is inspected for mechanical condition (belt tension, bearing wear, motor condition)
• The fan is reassembled and tested for proper operation

Step 6: Reassembly and Documentation

With all components cleaned:

• Filters are reinstalled in the correct orientation
• Plastic sheeting is removed from the kitchen
• The kitchen is inspected to ensure no water or chemical residue is left behind
• After photos are taken of every area that was cleaned
• The technician completes the compliance report
• A compliance sticker is placed on the hood with the date, company name, and next scheduled cleaning date
• A signed NFPA 96 compliance certificate is provided

What You Should See After: The Results

After a proper professional cleaning:

Hood Interior

• Stainless steel surfaces are visible and clean
• No grease film, discoloration, or residue
• The grease trough is empty and clean
• All seams and joints are free of grease

Filters

• Clean and free-flowing — you can see clearly through the baffle openings
• Properly oriented and seated in the hood
• No warping or damage (damaged filters should be flagged for replacement)

Ductwork

• Interior surfaces are clean to bare metal where accessible
• No grease buildup at elbows or horizontal runs
• All access panels are properly closed and sealed after cleaning

Fan

• Blades and housing are clean
• Catch pan is empty
• Fan is operational and running smoothly
• No grease leakage at the base

Documentation

• Before-and-after photos clearly showing the condition change
• Signed compliance certificate with date, technician name, and company information
• Sticker on the hood visible during any inspection
• Notes on any issues found (damaged filters, missing access panels, equipment concerns)

Red Flags: Signs of a Substandard Cleaning

Not all cleaning services deliver the same quality. Watch for these indicators that the job was not done properly:

• No before-and-after photos provided: A company that does not document its work has no accountability
• Residual grease visible on the hood interior: If you can see grease on the plenum walls after cleaning, the job is incomplete
• Filters still greasy after reinstallation: Filters should be clean
• No compliance certificate: Without documentation, you have no proof of cleaning for the FDNY or your insurer
• Quick service time: A single-hood system takes 3-4 hours minimum. If the crew was in and out in an hour, they did not clean the full system
• Kitchen is wet or dirty after service: A professional crew cleans up after themselves — the kitchen should be ready for operation
• No rooftop fan service: Some companies skip the fan entirely. This is unacceptable — the fan is part of the system
• Ductwork not addressed: If the company only cleaned the hood and filters but not the ductwork, the job is incomplete and your system is not compliant

For more guidance on evaluating cleaning providers, see our guide on how to choose a hood cleaning company.

Why Documentation Matters

The before-and-after documentation from your hood cleaning is not just a nice-to-have:

• FDNY compliance: Inspectors ask for certificates and may ask for photos. Having them ready demonstrates professionalism and compliance
• Insurance: If a fire occurs, your insurer will want to see maintenance records. Photo documentation is strong evidence of due diligence
• Dispute resolution: If you ever need to challenge a vendor’s work quality, photos from both parties provide an objective record
• Maintenance tracking: Comparing photos from cleaning to cleaning helps you understand how quickly your system accumulates grease, which informs your maintenance schedule

Bottom Line

A professional hood cleaning is a thorough, multi-hour process that leaves your entire exhaust system — from hood to rooftop fan — clean to bare metal. The documentation is as important as the cleaning itself. If your current provider is not delivering this level of service, it is time to switch.

Want to see what a proper cleaning looks like in your kitchen? Get a free estimate from Empire Hoods — we document every job with before-and-after photos and provide full NFPA 96 compliance certification.