When Custom Kitchen Hood Fabrication Makes Sense
Custom kitchen hood fabrication makes sense when a standard length, depth or shape will not fit the cook line, the ceiling or the route into the building. Catalog hoods come in set increments. Real kitchens have soffits, columns, sloped roofs and appliance lines that end 4 inches from a door frame.
Typical triggers for a custom build:
- A cook line that wraps a corner or follows an angled wall
- A display kitchen where the hood is part of the dining room design
- Low ceilings that need a shallow hood profile with the duct collar shifted to clear a beam
- A historic or high-rise building where every section has to fit a freight elevator or a stairwell
- A request to combine the hood, make-up air plenum, utility cabinet and lighting into one assembly
Custom does not mean unregulated. A fabricated hood still has to meet NFPA 96 and the locally adopted mechanical code, and the authority having jurisdiction (AHJ) reviews it like any other hood. For background on the hood categories themselves, see our Type I grease hood page.
Stainless Steel Gauges, Grades and Finishes
Most custom hoods are built from stainless steel, and the three choices that matter are thickness (gauge), alloy grade and surface finish. The code sets minimum material thicknesses for hoods; designers often specify heavier sheet than the minimum on exposed faces so the panels stay flat and resist dents.
| Choice | Common options | Where it is used |
|---|---|---|
| Gauge | 18 gauge for exposed canopy panels is a common shop standard; heavier sheet for large flat faces | Thicker sheet reduces oil-canning on wide, unbroken panels |
| Grade 430 | Ferritic stainless, magnetic | Standard hood bodies in dry kitchens; cost effective |
| Grade 304 | Austenitic stainless, better corrosion resistance | Wet or humid areas, coastal sites, exposed show kitchens |
| No. 4 finish | Brushed, directional grain | The usual exposed finish; hides scratches and cleans well |
| No. 2B or mill finish | Dull, non-directional | Concealed panels, tops and interior parts |
Grain direction is easy to overlook. On a long hood, all exposed panels should run the brushed grain the same way, and joints between sections should line up. Ask that the shop drawings note grain direction for show kitchens.
Confirm the minimum thickness required by the code edition your jurisdiction uses before releasing drawings, especially if the design calls for carbon steel or a material other than stainless.
Listed Hoods vs. Hoods Built to Prescriptive Code Requirements
A custom hood can be built one of two ways: as a listed hood produced under a manufacturer's UL 710 listing, or as a hood built to the prescriptive construction rules in NFPA 96 and the mechanical code. Both can pass inspection. They differ in how airflow is set and what the inspector looks for.
Listed hoods
A listed hood has been tested as a design, and the label tells the inspector the tested exhaust rates, clearances and filter arrangement. Many listed manufacturers can vary length, depth and some features within the limits of their listing. Exhaust rates are often lower than the code tables because the design was proven in testing. Fabricators without their own listing can sometimes source listed components or partner with a listed manufacturer; we do not represent our shop work as carrying a UL listing.
Prescriptive (unlisted) hoods
An unlisted hood is built to the construction requirements written into the code: material thickness, liquid-tight welded seams, grease troughs, filter installation and clearance to combustibles. Exhaust rate comes from the code tables for the appliance duty class, which usually means more airflow than a comparable listed hood. In return, the geometry is limited only by the code and the room.
Which route fits depends on the shape you need, your energy goals and what your AHJ prefers. Some jurisdictions are comfortable with either; others ask for extra documentation on unlisted hoods. Our kitchen hood design and engineering team can help decide before drawings are drawn.
Shop Drawings: The Document Everything Else Waits On
Shop drawings are the fabricator's dimensioned drawings of the hood, and nothing gets cut until they are approved. They are where the owner, the architect, the mechanical engineer and the suppression contractor all see the same hood for the first time.
A complete set of custom hood shop drawings typically shows:
- Plan, elevation and section views with overall and panel dimensions
- Appliance line under the hood, with overhangs dimensioned
- Duct collar size and location, plus make-up air collar if integrated
- Filter sizes, quantity and arrangement
- Light fixture locations and electrical connection points
- Suppression piping penetrations and utility cabinet layout
- Hanger locations and the weight to be carried by the structure
- Section breaks and field joint details if the hood ships in pieces
- Material grade, gauge and finish callouts
Review the hanger loads with the structural engineer early. A long custom hood with an integrated plenum can be heavy, and hanging it from a roof deck that was never designed for the load is a problem better found on paper.
Field Dimensions and Oddly Shaped Spaces
Field dimensions are measurements taken in the actual space after framing, and a custom hood should be built to them rather than to the architectural plans. Walls end up an inch off square, ceilings vary along a long run, and a column shown as 12 inches is furred out to 16.
What to measure
- Wall lengths at hood mounting height, not only at the floor
- Ceiling height at several points along the hood length
- Locations of beams, joists, sprinkler mains and existing ductwork above the hood
- Corner angles where the line turns
- Door, corridor and elevator openings on the delivery path
Common odd-shape solutions
An L-shaped or angled cook line can be served by a hood built with a mitered corner section. A sloped ceiling can be handled with a stepped top or a filler panel that follows the slope while the capture edge stays level. A column in the middle of the line can be wrapped with a stainless enclosure and the hood notched around it, as long as the notch does not reduce coverage over cooking surfaces.
Every unusual feature needs to be checked against capture: a hood can look perfect and still spill smoke if a notch or a short section leaves an appliance edge uncovered.
Integrated Make-Up Air Plenums and Utility Cabinets
A custom hood can include a make-up air plenum along its front or sides, delivering replacement air close to the hood without blowing across the capture area. The plenum style changes how the air enters the room, and that affects capture.
| Plenum style | How air is delivered | Notes |
|---|---|---|
| Front face (perforated) | Low velocity, downward and outward from the hood front | Common choice; keeps air away from the plume |
| Back supply | Down the back wall behind the appliances | Needs space behind the line; check with appliance clearances |
| Short-circuit (internal) | Released inside the hood | Often restricted; confirm with the AHJ before specifying |
Utility cabinets are enclosures built onto one end of the hood to house the suppression tank and controls, fan and light switches, or a fan control panel. They keep wall space free and put the controls where cooks can reach them. Plan the cabinet with the suppression contractor so the tank, piping and pull cable all fit.
Sizing and tempering the air itself is covered on our make-up air system page.
Shipping a Custom Hood in Sections
Large custom hoods are often built and shipped in sections, then joined in the field. Section length is chosen to fit the truck, the loading dock and, most often, the narrowest point on the path to the kitchen: a door, a corridor turn or an elevator cab.
Field joints are typically bolted and sealed, with the joint located so that grease does not collect in it. The exterior trim is designed so the finished hood reads as one piece. Each section should arrive labeled to match the shop drawings, with hanger points and the joining sequence marked.
- Confirm delivery path dimensions before the shop sets section lengths
- Arrange equipment to lift sections into place (lifts or rigging)
- Protect finished faces in transit with film that comes off cleanly
- Keep filters, light lenses and loose trim in separate labeled crates
Our commercial kitchen hood installation crews handle sectional assembly, leveling and sealing on site.
Getting a Custom Hood Priced and Built
Pricing a custom hood starts with drawings and an equipment list, not a length in feet. The more the fabricator knows about the room and the cook line, the fewer revisions the shop drawings go through.
- Send the floor plan, reflected ceiling plan and equipment schedule.
- Note any architectural requirements: exposed finish, lighting, color or trim.
- Identify constraints such as structure above, delivery path and existing duct.
- Review preliminary shop drawings and mark up changes.
- Verify field dimensions once framing is complete, then release for fabrication.
When you are ready, send drawings for a custom hood quote.
Custom Hood Fabrication Questions
- Is a custom fabricated hood harder to get approved?
- Not necessarily. Inspectors approve custom hoods routinely, provided the construction follows NFPA 96 and the local mechanical code and the submittal shows materials, seams, filters, clearances and exhaust rates clearly. Unlisted hoods may need more documentation than listed ones. Talking to the AHJ during design avoids surprises at plan review.
- Should I choose 430 or 304 stainless for my hood?
- Grade 430 is common for hood bodies in typical kitchens and costs less. Grade 304 resists corrosion better and suits humid kitchens, coastal locations and exposed show hoods where appearance must hold up for years. Many hoods mix the two, with 304 on exposed faces and 430 on concealed parts, so long as the drawings call out each one.
- Can a custom hood be painted or clad in another material?
- Decorative cladding or powder coating on exterior surfaces is sometimes possible, but anything near the capture area or inside the hood must stay bare, cleanable steel. Combustible decorative materials need clearance from the hood just like any combustible construction. Confirm with your AHJ before committing to a finish other than stainless.
- Why build to field dimensions instead of the architectural plans?
- Plans show design intent, while the built space always differs a little. Walls drift, columns are furred out and ceilings vary. A hood built to plan dimensions may not fit between walls or may hit a beam. Measuring after framing removes that risk and lets the shop build trim and filler panels that close gaps cleanly.
- How are hood sections joined in the field?
- Sections are usually bolted together through flanges and sealed with a material suited to the location, with the joint arranged so grease does not pool in it. The exterior is trimmed to look continuous. Joining details appear on the shop drawings so the inspector and installer know what to expect before the hood arrives.
- Can you build a hood to match an existing one in my kitchen?
- Usually yes, if the existing hood can be measured and its construction matched. For an addition next to an older hood, the new section is often built as a separate hood with its own collar, or the whole line is reviewed so airflow and suppression still work together.