Commercial Hood & Ventilation Guide: Type I vs. Type II, CFM Sizing, and Makeup Air

Ventilation is the piece of a commercial kitchen buildout that everyone budgets last and everyone regrets first. A cook line is only as good as the air moving over it — undersized exhaust turns your grill into a smoke machine, oversized exhaust starves the space of makeup air and slams doors on hinges, and the wrong hood type over the wrong equipment fails inspection before you serve your first plate.

This guide walks through what actually matters when you're spec'ing hoods and ventilation for a restaurant, ghost kitchen, bar, or school cafeteria: the Type I vs. Type II distinction, how to size CFM the way engineers actually size it, why makeup air is the piece nobody warns you about, and where NFPA 96 draws hard lines you don't get to negotiate. Pair this with our commercial range buying guide and fryer buying guide — the equipment on your cook line dictates the hood above it, not the other way around.

Type I vs. Type II: the only distinction that actually matters

Every commercial kitchen hood on the market falls into one of two categories, and the difference is not cosmetic — it's what's coming off the equipment underneath.

• Type I hoods handle grease-laden vapor. That means anything that produces smoke or aerosolized fat: ranges, fryers, griddles, char-broilers, salamanders, wok ranges, rotisseries, and heavy-duty broilers. Type I hoods are required to have grease-baffle filters, a code-listed exhaust duct, and a UL 300 fire-suppression system (usually Ansul R-102).
• Type II hoods — sometimes called condensate or heat/vapor hoods — handle steam, heat, and non-grease vapor. That means dishwashers, steamers, kettles, some combi ovens (in steam mode), pasta cookers, and pan-warmers. Type II hoods don't need grease filters and don't require fire suppression; they're a lot cheaper, and they can vent into simpler ductwork.

The rule of thumb: if smoke or grease vapor rises off it, you need a Type I hood. If it's only steam or dry heat, a Type II condensate hood is code-compliant and half the money.

You cannot substitute a Type II for a Type I. The reverse — putting a Type I over a dishwasher — is legal but wasteful; you're paying for fire suppression and grease filters you'll never use. Match the hood to the equipment.

The "combi oven grey area"

Combi ovens are the one place spec engineers argue. Boilerless combis in convection-only mode produce almost no grease-laden vapor; the same oven in combi mode with proteins can produce meaningful grease over time. Manufacturer guidance controls: Rational and Alto-Shaam both publish hood-type requirements for each model. Ventless combi ovens (with internal grease and carbon filtration) sidestep the question entirely and are a huge deal for tenant buildouts where cutting the roof isn't an option. See our combi oven buying guide for the full breakdown.

Sizing CFM: what "700 CFM per linear foot" actually means

Every hood spec sheet gives you a CFM rating — the volume of air the exhaust fan pulls, measured in cubic feet per minute. Undersize it and grease vapor rolls into the dining room. Oversize it and you'll burn energy exhausting conditioned air you paid to heat or cool. Both mistakes are expensive.

There are two ways engineers calculate required exhaust CFM. Most restaurant projects use the duty-classification method, which sizes CFM based on the type of equipment under the hood:

Duty class	Typical equipment	CFM per linear foot (wall canopy)
Light-duty	Ovens, steamers, kettles, pasta cookers	150–200 CFM/ft
Medium-duty	Ranges, fryers, griddles, tilt skillets	200–300 CFM/ft
Heavy-duty	Char-broilers, upright broilers, chain broilers	300–400 CFM/ft
Extra-heavy-duty	Solid-fuel (wood, charcoal), open-flame woks	400–550 CFM/ft

The hood length is the horizontal run of hood in feet — not the equipment length. Code (IMC and NFPA 96) requires a 6-inch overhang on each end for wall-canopy hoods, so a 60-inch range battery needs a 72-inch hood minimum. A 48-inch char-broiler needs a 60-inch hood.

Worked example: a small diner cook line

Say you're spec'ing a Type I wall-canopy hood over a 36-inch Vulcan range, a 36-inch flat griddle, and a 15-inch single-tank fryer. That's an 87-inch equipment run, so you need a 99-inch (roughly 8'3") hood with 6" overhangs.

• Range and griddle are medium-duty — call it 250 CFM/ft × 6 feet = 1,500 CFM.
• Fryer bumps the local rate at that end. Some engineers pull the whole hood at the highest duty class present; a conservative sizing lands around 275 CFM/ft × 8.25 ft ≈ 2,270 CFM.

Round up to ~2,300 CFM and spec a hood/fan combo that hits that at the fan curve after static-pressure losses. If you swap the fryer for a char-broiler, you're at 300 CFM/ft or higher for the whole run and pushing 2,500–2,800 CFM.

Wall canopy vs. island vs. back-shelf vs. proximity

Once you know the CFM you need, the hood style is driven by where the cook line lives in the room.

• Wall canopy — mounted against a wall, cooking equipment against the wall too. Cheapest to fabricate, easiest to capture vapor because the wall does half the work. Default choice for 80% of restaurant buildouts.
• Single-island canopy — the cook line is in the middle of the room. No wall to catch drift, so island hoods run ~25% higher CFM than an equivalent wall-canopy at the same duty class. Common in show kitchens.
• Double-island canopy — cooking equipment on both sides of a shared island hood. Same higher CFM penalty; use only when the floor plan actually requires it (rare).
• Back-shelf / low-proximity — a shorter, closer hood that sits directly behind and low over the equipment. Very efficient at capturing vapor with lower CFM (sometimes 30% less than a wall canopy), but only works with lower-profile equipment (griddles, small fryers, sandwich units) and won't fit over anything with a tall salamander or oven back. Excellent for tight footprints.
• Pass-over — a specialized back-shelf variant for pizza and display cooking lines.

Makeup air: the trap that fails inspections

Here's the piece nobody warns first-time restaurant owners about: every cubic foot of air your exhaust hood pulls out of the building has to be replaced. If it isn't, the kitchen goes into negative pressure, and bad things happen — front doors are hard to open, back doors slam, HVAC systems fight themselves, gas appliances back-draft (a real safety issue), and cooking odors get pulled into the dining room instead of pushed out the roof.

The mechanical code (IMC 508) requires makeup air (MUA) for any hood exhausting over 400 CFM — which is essentially every commercial hood. The MUA unit is a separate piece of rooftop equipment that draws outdoor air, filters it, tempers it (heats or cools it in extreme climates), and delivers it back into the kitchen so the building stays in slight positive or neutral pressure.

How MUA is sized

Rule of thumb: MUA delivers 80–90% of exhaust CFM, with the remaining 10–20% coming from the building's HVAC transfer air (dining room supply pushed toward the kitchen). If you're exhausting 2,300 CFM, you need a MUA unit delivering roughly 1,900–2,050 CFM. In cold climates, MUA also has to be heated — a natural-gas fired MUA unit sized for a Chicago winter can add real capital and operating cost, so factor it into your true equipment budget from day one.

Short-circuit MUA vs. properly tempered MUA

You'll see spec packages offering "short-circuit" or "in-hood" MUA — a plenum that dumps cool outdoor air right at the front lip of the hood, on the assumption it gets sucked straight up without ever entering the kitchen. It sounds elegant. It's largely fallen out of favor: capture efficiency suffers, cooks stand in the cold air draft, and in humid climates you get condensation problems. Most modern designs put MUA through a ceiling diffuser or a wall-mounted grille several feet away from the hood, tempered to a reasonable temperature.

Fire suppression, NFPA 96, and what the AHJ actually checks

Every Type I hood in the United States has to have a UL 300–listed wet-chemical fire-suppression system. In practice, that means an Ansul R-102 or Amerex KP system integrated with the hood, with nozzles aimed at each cooking appliance, a fusible-link detection line running through the plenum, and interlocks that shut off gas and electric to the cook line when the system discharges.

The relevant code is NFPA 96 ("Standard for Ventilation Control and Fire Protection of Commercial Cooking Operations"). The bullet points that matter for someone spec'ing a system:

1. Fusible-link detection over every appliance under the hood. If you add a fryer or move a char-broiler after install, the suppression nozzles have to be re-aimed. This is not a "we'll figure it out later" line item.
2. Semi-annual inspection and cert (UL 300). A licensed fire-suppression contractor has to inspect the system every six months. Miss a cert and your insurance and your permit both go sideways.
3. Grease-duct cleaning frequency depends on cooking volume. Solid-fuel operations: monthly. Heavy-use fryer/broiler lines: quarterly. Moderate use: semi-annually. Light use (pizza, low-volume): annually. Keep the invoices — inspectors ask for them.
4. Duct construction is spelled out to the inch. 16-gauge welded black-iron or 18-gauge welded stainless, continuous slope back to the hood, cleanouts at every change of direction, minimum clearances to combustibles (or listed grease-duct wrap to reduce them).

None of this is optional. Talk to your AHJ (Authority Having Jurisdiction — usually the local fire marshal) before your plumbing is finalized, because ductwork routes and fire-rated shafts are much cheaper to plan than to retrofit. The OSHA workplace-safety rules layer on top of NFPA 96, particularly around interlocks and emergency-shutoff placement.

Ventless hoods: when cutting the roof isn't an option

Not every kitchen has the option to punch through the roof to an exhaust fan. Ghost kitchens, food halls, historic buildings, hotel-suite tenant spaces, and second-floor buildouts often forbid new roof penetrations. That's where ventless hood systems come in.

A ventless system self-contains all filtration — grease baffles, HEPA-grade or ESP (electrostatic precipitator) stages, and activated-carbon odor filters — and recirculates the cleaned air back into the kitchen. Fire suppression is integrated. Because there's no exhaust duct, there's no makeup-air unit either. The tradeoffs:

• Equipment cost is higher up front. A ventless setup with UL 710B or KNLZ listing runs $12,000–$40,000 depending on cooking load — comparable to a vented setup including MUA and roof work, but you pay it all as capital equipment instead of splitting it across trades.
• Filter replacement is real. Carbon and HEPA filters need periodic replacement (every 3–12 months depending on volume), and the filtration cartridges aren't cheap.
• Equipment is constrained. Ventless hoods are UL-listed to specific equipment lists — often ventless combi ovens, ventless fryers (fully enclosed with integrated filtration), and low-emission electric griddles. You can't just put any range under a ventless hood.

For ghost-kitchen operators and food-hall tenants, ventless is often the only path to opening. Pair it with a ventless fryer and a boilerless combi oven and you can run a serious menu without a single roof penetration.

Hood filters, cleaning, and the maintenance nobody plans for

Filters are the maintenance item everyone underestimates. Every Type I hood has a row of stainless-steel baffle filters — mandated by NFPA 96, listed under NSF Standard 2, and required to be washable. Aluminum mesh filters are illegal for grease capture (they don't drop hot grease back into a collection trough, they clog and drip). If you inherit a used hood with aluminum mesh, replace it — Alto-Shaam Ventech, Kason, and generic replacement stainless baffles all drop in for well under $200 each.

Cleaning schedule that keeps you inspection-ready:

• Daily: wipe the hood exterior and drip trough. Empty the trough into a grease-collection container.
• Weekly: pull the baffle filters, run them through the dishwasher on a heavy cycle (or hand-degrease in a sink), reinstall.
• Quarterly to semi-annually: licensed grease-duct cleaning per NFPA 96 based on cooking volume. Certificate stays posted near the hood.
• Semi-annually: UL 300 fire-suppression inspection. Also inspect fusible links (they get replaced on schedule).

Skip any of these and you're one grease fire away from a total loss. Insurance companies check.

Brand landscape: the manufacturers that show up on real drawings

Hood manufacturing is more consolidated than you'd think. In the US, three brands dominate large commercial jobs, plus a handful of specialists for smaller or ventless applications:

• CaptiveAire — the largest US commercial-hood manufacturer. Complete packages (hood + fan + curb + MUA + controls) with quick lead times. Standard on most mid-market restaurant projects; not sold direct through us, but the design language is the reference point.
• Halton — Finnish, premium tier. Capture Jet technology reduces required CFM 20–40%, which pays back on energy over a few years. Used on high-end fine-dining and hospitality jobs.
• Accurex — a Greenheck brand, mid-market, strong integrated packages.
• Vulcan — for condensate hoods matched to specific Vulcan Mini Jet steamers and other Type II applications.
• Advance Tabco and John Boos — Type II condensate-hood specialists, well-known for stainless fabrication quality. USA-RS carries Advance Tabco 42x42 condensate hoods, John Boos 60-inch box-type condensate hoods, and other stock sizes for dishroom and low-heat applications.
• Krowne — back-bar and underbar exhaust-only hoods for glass washers and bar equipment. See the exhaust-only hoods collection for stock sizes like the Krowne A1616.
• Alto-Shaam — filters and ventless hood accessories for their Vector and Ventech lines; their Ventech Type I hood washable grease filter is a common drop-in replacement.
• Unox — ventless carbon-filter hood systems designed for their ChefTop combi ovens; increasingly common for tenant buildouts.

Common ventilation mistakes and how to avoid them

1. Buying a hood before you've picked your cook line. The equipment sets the CFM, the duty class, the length, and whether you need Type I or Type II. Do the equipment list first.
2. Skipping the MUA. The exhaust price gets a green light because "it's just the hood," and the MUA quote arrives after the mechanical inspection. Don't. Bid both together.
3. Undersizing the hood length. A 6" overhang each side is minimum — some jurisdictions want 12" on the fryer end. Read the local amendment.
4. Cheap hood, no fire suppression package. The hood is only part of the equipment package. Ansul (or equivalent) is 15–25% of the ventilation total, and it's non-negotiable for Type I.
5. Ignoring roof structural. A 3-ton MUA plus a big exhaust fan plus a curb is 1,500+ pounds of dead load. Have the roof looked at before you buy.
6. Buying an oversized hood "for the future." Oversized hoods pull too much conditioned air, waste energy, and destabilize the kitchen. Right-size for today, plan a re-spec if you ever add heavy-duty equipment.

Keep reading

• Commercial Range Buying Guide: Gas vs. Electric, BTUs, Burners, and the Brands That Actually Last
• Commercial Fryer Buying Guide: Gas vs. Electric, Tube-Fired vs. Flat-Bottom, and Real ROI
• Combi Oven Buying Guide: Boiler vs. Boilerless, and the Brands Worth the Premium
• Char Broiler Buying Guide: Radiant vs. Lava Rock vs. Ceramic

Ready to spec your ventilation package?

Ventilation is the trade where cheaping out shows up as failed inspections, back-drafting appliances, and doors that won't stay closed. Start by picking the cook line — then let the equipment dictate hood type, CFM, filter class, and makeup-air. Browse our hoods and ventilation collection, the commercial kitchen hoods lineup, Type II condensate hoods for dishrooms and steam equipment, ventless hood systems for tenant buildouts, or the full USA-RS catalog. For a project-scale bid — hood, fan, MUA, ducting, and fire suppression as one package — contact our team and we'll match the spec to your cook line and your local code officials.