Choosing the wrong laboratory fume hood exhaust duct is an expensive mistake: the duct run carries every chemical fume the hood collects, and it has to survive them for the life of the lab. The mistake usually comes from treating duct selection as a single “which material” question. In practice the decision chain starts with airflow, then material, then duct type and size, then installation and review boundaries. This guide walks that chain for a laboratory fume hood exhaust duct: face velocity and airflow, a material decision matrix for PP, PVC, CPVC, FRP, and stainless steel, round versus square sizing, installation details, and the checklist to hand your engineer or manufacturer. One boundary up front: face velocity, fan, and pressure-drop design stay with the system engineer — this page gives the screening numbers, not the final design.
Key Takeaways
- A laboratory fume hood exhaust duct is the rigid ductwork that carries chemical fumes from the hood to the roof outlet, and PP is the practical default for most acid and base lab exhaust.
- Design from airflow first. Face velocity × open sash area sets the CFM you must move; a typical 4 ft hood at 100 fpm needs about 450 CFM.
- Match the material to the worst-case medium and temperature. PP to about 90°C, PVC to about 60°C, CPVC to about 93°C, FRP and stainless steel for the cases that outrun them.
- Size the duct between about 1,000 and 2,000 fpm, then confirm with your engineer. 450 CFM at 1,500 fpm works out to a 7.4 in round duct, or a 200 mm PP duct.
- Ductless hoods need institutional approval and filters matched to your chemical list. Corrosive, high-hazard, or unknown mixtures stay ducted.
Direct Answer: What Duct Do Laboratory Fume Hoods Need?
A laboratory fume hood exhaust duct in PP is the practical default for acid and base fumes at essentially ambient temperature. The material decision follows the worst-case chemical list: PP carries most water-based acids and bases to roughly 90°C, Type 1 PVC (uPVC) is the common US alternative with a lower ceiling near 60°C, CPVC extends PVC-type chemistry to about 93°C, FRP steps in for aggressive acids including hydrofluoric acid with resin-dependent limits near 121°C, and 316 stainless steel suits solvent-heavy exhaust at a higher cost. Galvanized steel is the wrong answer for corrosive laboratory exhaust: its zinc coating and base metal are attacked by the acid and alkali fumes that a chemistry lab generates, which is why manufacturers and design firms specify plastics or stainless steel instead.
The system the duct belongs to has five elements in series: the hood itself, the duct run from hood to fan, the exhaust fan, the roof termination, and the supply air that replaces what the fan removes. The duct is the element this page decides; the fan and the supply air are engineered around the duct, not the other way around. That is why the airflow numbers come first in this guide: they define what the duct must carry, and the material choice follows the chemistry of what it carries.
The airflow side is just as important. Design the system from the hood’s face velocity, convert it to airflow through the open sash area, then size the duct at a velocity that keeps fumes moving without excessive pressure loss. Sections below give the numbers for each step, a decision matrix for materials, and the worked example that ties the chain together.
The input that drives everything is the chemical list, and it decides the outcome before any material comparison does. A hood that runs concentrated hydrochloric acid in the morning and acetone vapor after lunch presents two different challenges to the duct: the acid drives the corrosion requirement, the solvent drives the compatibility check, and the hotter of the two sets the temperature floor. That is why the sections below build the answer from airflow and worst-case chemistry instead of from a generic “best duct” claim — the right material for one lab can be the wrong material for the one next door.
This page decides the screening answer: airflow, candidate material, duct type and size, installation notes, and the boundary where your decision stops. It does not decide the fan, the pressure drop, the supply air, or the fire classification — those belong to the system engineer and the project authority. You take the numbers from the first five sections, and the engineer turns them into a working system.
Decision point: after this module you can decide whether the chain below fits your project and which numbers you will need to gather before you start.
Fume Hood Exhaust Design Starts with Face Velocity and Airflow
The two numbers that anchor the whole design are the face velocity at the hood opening and the airflow it produces. Face velocity is a measure of containment: it is the average air speed that keeps room air flowing into the hood instead of letting fumes escape into the breathing zone. Airflow is what the duct actually has to move. Confusing the two is the most common error in lab exhaust discussions, so this section separates them cleanly before any material decision happens.
Face velocity: about 0.5 m/s (100 fpm) is the design target
Face velocity is the average air speed measured across the hood opening with the sash at its operating position. The common design target is about 0.5 m/s (100 fpm): acceptance specifications commonly call for an average of 80–120 fpm with the sash at 18 inches and no single reading more than ±20 percent from that average, in the context of the ANSI/AIHA Z9.5 ventilation standard. Hood manufacturers describe a recommended operating band of 0.3–0.5 m/s. The exact figure belongs to the project specification, not to a material page.
Face velocity is fragile in practice. A person walking past the hood can create enough turbulence to disrupt a 0.5 m/s (100 fpm) flow, and a supply diffuser blowing toward the hood can erase it entirely. That is why hood placement rules keep hoods out of main traffic paths and keep directional diffusers away from the face. The velocity itself is also not uniform across the opening: the average is what acceptance testing verifies, with the ±20 percent tolerance covering the spread between individual readings at the prescribed grid of measurement points.
In US laboratories the OSHA laboratory standard (29 CFR 1910.1450) frames the ventilation and exposure-control requirements the whole hood system must meet. Acceptance testing follows the ANSI/ASHRAE 110 test method, which measures how well the hood contains a tracer gas — the reason the face-velocity number matters is containment, not comfort. A hood that passes its containment test at the target velocity protects the user; a hood that merely moves air without containing it protects no one.
Airflow: face velocity × open sash area
The airflow a hood needs is the product of face velocity and the open sash area: Q = V × A. A 4 ft hood with an 18 in sash (1.5 ft) and a 3 ft wide opening presents 4.5 ft², so at 100 fpm it moves about 450 CFM, roughly 764 m³/h. Add the hoods on the same system with a simultaneous-use factor before you size the main duct; two hoods that each need 450 CFM but are never fully open at once may need only 700–800 CFM of combined capacity, while fully loaded chemistry suites add the full amount. Manifolded systems combine the flows, while NFPA guidance keeps incompatible chemicals on separate runs.
The sash position matters as much as the velocity. At a lower sash the opening area shrinks, so the same airflow produces a higher face velocity — which is why hoods are tested and operated at a defined sash height. If the airflow is fixed and the sash opens wider, face velocity drops, and containment degrades. This single relationship drives the choice between constant-volume and variable-air-volume (VAV) hood controls later in the design, and it is the reason the worked example in this guide states its sash position explicitly.
This is a screening calculation, not the final system design. It gives you the airflow input that drives duct size in the next section; fan selection, pressure drop, and balancing are the engineer’s scope. Write down the number you get — the worked example later uses exactly this method.
Decision point: after this module you can compute your lab’s exhaust airflow from face velocity and sash geometry and choose a simultaneous-use factor for the hood count.
Choosing Duct Material for Lab Exhaust: Media and Temperature
For a laboratory fume hood exhaust duct, the material matrix below is the core of the decision. Read it as “worst case wins”: the hottest, most corrosive chemical in the hood sets the floor for the duct material, because the duct sees every experiment, not just the routine ones. Two inputs fix the row of the matrix: the chemical family of the worst-case medium, and the temperature at which that medium is exhausted. Everything else — joint method, cost direction, duct geometry — is secondary to those two.
| Material | Continuous temperature (typical) | Chemical fit | Joint / connection | Cost direction | Pick when |
|---|---|---|---|---|---|
| PP (polypropylene) | about 90°C, grade- and load-dependent | Acids, bases, aqueous salts; solvents checked per chemical | Extrusion-welded or flanged | Moderate | Default for acid/base lab exhaust |
| PVC Type 1 (uPVC) | about 60°C | Many acids and aqueous chemicals; some solvents incompatible | Solvent-cemented | Moderate | US default, lower temperature ceiling than PP |
| CPVC | about 93°C | Similar to PVC, higher temperature rating | Solvent-cemented | Above PVC | Hotter acid service |
| FRP (fiberglass reinforced plastic) | about 121°C, resin-dependent | Aggressive acids incl. hydrofluoric; confirm grade | Resin-bonded or flanged | Higher | Strong acids, higher temperature |
| 316 stainless steel | not a service rating; melting far above plastics | Solvents; chloride service needs grade review | Welded | Highest | Solvent-heavy or fire-conscious runs |
PP: the default for acid and base lab exhaust
PP resists the water-based acids, bases, and salts that dominate chemistry-lab exhaust, and its continuous service temperature lands near 90°C with the exact value tied to grade and load. For a hood that exhausts hydrochloric acid in the morning and sodium hydroxide after lunch, PP sits inside that band directly. The solvent side is the boundary: not every organic vapor is inert to PP, so check each solvent against a resistance chart before specifying it.
PP also behaves well in a duct run. Continuous extrusion-welded seams keep the corrosive stream away from joints, flanged connections allow periodic disassembly, and the material’s low density keeps roof and hanger loads modest. When the medium list is stable and ambient, PP is the starting candidate — and the reason most US and European lab duct systems in acid/base service end up in PP rather than in metal.
PVC and CPVC: the US default with a lower temperature ceiling
Type 1 PVC is the traditional US lab ductwork material: it resists a wide range of acids and is often the first material a US manufacturer names. Its limitation is temperature — continuous service near 60°C — and its brittleness relative to PP, which matters in cold roof runs and rough handling. Solvent-cemented joints are standard; some solvents are not compatible with PVC, so the chemical compatibility chart governs.
CPVC raises the temperature ceiling to about 93°C with similar chemistry. When a lab’s acid exhaust runs hotter than PP or PVC comfortably carry, CPVC is the intermediate step before FRP or stainless steel. The trade-off is that both PVC and CPVC stay brittle at low temperature compared with PP, so a roof run in a cold climate needs protection from impact and thermal shock that PP tolerates better.
FRP, stainless steel, and when to step up
FRP’s temperature and chemical limits follow the resin system, commonly quoted around 121°C for vinyl ester, and it is the material family to consider for strong acids, including hydrofluoric acid, where thermoplastics need grade confirmation. Always request the manufacturer’s chemical resistance data sheet for the specific resin — no single FRP grade covers every effluent, and the resin system (vinyl ester, polyester, or epoxy) changes both the temperature limit and the chemical list.
316 stainless steel suits solvent-heavy exhaust that would soften or dissolve plastics, and its corrosion resistance comes from the chromium oxide passive layer that self-repairs. The 316 grade adds molybdenum for better chloride and pitting resistance than 304. It costs more and carries its own chemical limits — reducing acids and high-concentration chlorides can attack the passive layer — so the selection returns to the worst-case list. The corrosive-selection guide and the duct materials comparison page cover these boundaries in depth.
Decision point: after this module you can name the one or two candidate materials for your lab’s exhaust from the matrix, and you know which step-up paths exist when the medium outruns them.
Round or Square: Duct Type and Size Ranges
Once the material is bracketed, the geometry question is round versus square, and then the size. Both geometries are common in laboratories, and the choice is governed by the space available and the pressure budget — not by habit. This section gives the mechanism for each geometry, then the sizing method that turns airflow into a duct size.
Round vs square duct for laboratory runs
For a laboratory fume hood exhaust duct, round and square are the two practical geometries. Round duct is preferred where velocity uniformity matters: the cross-section keeps velocity even, resists settling and eddies, withstands higher static pressure, and seals more easily. A round section also carries the same airflow in less surface area, which means less material and less friction loss for the same flow.
Square duct trades some of that uniformity for headroom — it tucks against walls and above benches, which is why laboratory runs often use square sections, and it mounts flat against a wall or chase without the standoff hardware a round duct needs. The difference is a trade, not a verdict: a long run with tight pressure head favors round; a wall-hugging run in a low-ceiling lab favors square.
Both are common in labs; choose by the space and the pressure budget, not by habit. The joint decision runs parallel: continuous welded seams for aggressively corrosive exhaust, flanged joints where the run needs periodic disassembly for cleaning or reconfiguration. Either way, the duct slopes back toward the hood so condensed liquid drains instead of pooling in horizontal runs.
Sizing the duct from airflow
Duct velocity is the link between airflow and size. Keep the flow fast enough to prevent settling — industry guidance puts the practical floor near 500 FPM, because below that velocity particulates and condensate deposit in horizontal runs and elbows — and slow enough to control pressure drop, energy, and noise, with main-system velocities commonly capped around 2,500 FPM. A screening band of 1,000–2,000 FPM fits most lab exhaust; the sizing guide covers the calculation method in full.
For a round duct, diameter comes from the airflow and chosen velocity: Q = V × A, so 450 CFM at 1,500 FPM needs about 0.3 ft² of area, a diameter near 7.4 in. A square duct uses an equivalent diameter of 2ab/(a+b) for the same friction behavior, so a 200 × 200 mm square section lands in the same performance class as a 200 mm round duct. Standard PP sizes run in the φ20–600 mm family — the common 200 mm duct covers the 7.4 in case directly — with larger sizes fabricated by sheet welding and confirmed against the project quotation.
If the run is short and velocity is the constraint, sizing up one standard size reduces pressure loss at modest cost. If the run is long and the building has tight chase space, the square geometry may fit where a round duct would not, even at the same equivalent diameter. Both levers — size and geometry — are available at the same airflow; the point is to move the air at the chosen velocity with the least penalty in space and pressure.
Decision point: after this module you can pick round or square and a standard duct size from your computed airflow, and you know when to size up.
Installation and System Composition
A duct specification that stops at material and diameter is incomplete. The installation details — routing, expansion, supports, and the fittings that make the run a system — determine whether the corrosion-resistant material actually survives in service. This section covers the three installation areas that most often fail in real lab projects.
Routing, elbows, and condensate
Every bend adds resistance, and in corrosive service it also invites condensation. A 12 in diameter elbow adds roughly 25 ft of equivalent straight-duct resistance, so route with the fewest turns, add at least 3 ft of straight duct before and after each elbow for the air to straighten, and slope horizontal runs back toward the hood so condensate drains. Terminate with a zero-pressure weather cap, not a cone or gooseneck — the cap discharges vertically with minimal static pressure loss.
Condensation is the corrosive failure mode that routing controls. Warm, humid exhaust meets a cold roof run, moisture condenses, and the condensate is not water — it is the diluted chemical load of the exhaust, which is exactly what the duct material was chosen to resist. Keeping the condensate draining back to the hood instead of pooling in elbows is what protects the run over years of service.
These routing rules are the cheapest part of the system to get right, because they are locked in at layout time. Changing a duct route after installation means cutting into a corrosive-exhaust run, so the layout review happens before fabrication, not after.
PP expansion, supports, and welded or flanged joints
PP expands roughly ten times more than steel: the linear thermal expansion coefficient runs about 0.10–0.15 mm/m·°C versus about 0.012 for carbon steel. A 30 m roof run on a hot day can grow by 120–180 mm, so long straight sections need expansion compensation — bellows, expansion joints, or deliberately placed offsets — and supports that allow movement. Roof penetrations need a weatherproof collar that seals around the duct without locking it in place.
The stiffness trade-off matters for hanger spacing: PP’s elastic modulus is about 1.3–1.8 GPa against roughly 200 GPa for steel, so plastic ducts sag between supports unless hangers are closer together than a steel run would need. Its density near 0.90–0.91 g/cm³, about one-eighth of steel, keeps the total load light even with more supports. The two properties work together: the duct is light but flexible, so the support scheme has to hold it firmly without pinning it rigidly against thermal movement.
Welded joints give continuous corrosion resistance; flanges give access. Both are legitimate — the choice follows the need to open the run. A run that never needs internal inspection can be welded end to end; a run with dampers, cleanouts, or periodic cleaning requirements wants flanged access points at those locations. The joint method is part of the specification, not an afterthought at installation.
Duct system components
A lab exhaust run is more than straight pipe. The system includes elbows and tees, round-to-square or round-to-round transitions, dampers (backdraft dampers prevent reverse flow when hoods share a manifold, butterfly and blast-gate dampers balance airflow), a rain skirt where the duct passes the roof, and the discharge weather cap. Each component has a defined job: transitions change geometry without changing the flow direction, dampers control or isolate flow, and the cap protects the opening from weather while discharging upward.
Order the components with the duct itself so dimensions and joint types match from the first fitting to the last. Mixing joint systems — welding one section and solvent-cementing the next, or mating a flanged component to a welded run without an adapter — is where corrosive exhaust finds its leaks. Specify the whole assembly as one system, and confirm the joint method of every component against the duct’s own connection type.
Decision point: after this module you know the routing, support, expansion, and component list your installation must include, and which joint and compensation choices fit your run.
When Ducted Exhaust Is Not the Answer (and When to Stop Self-Designing)
Two boundaries limit where a duct-material guide applies. The first is the ductless alternative, which replaces the duct with filtration; the second is the set of design decisions that belong to the engineer, not to a material selection. Knowing both boundaries is part of the design — it keeps you from specifying a ducted system that should have been filtered, and from deciding fan and fire details you are not equipped to decide.
Ductless hoods: approval and chemical-match limits
Ductless hoods filter exhaust through carbon or other media and recirculate the air, which makes them attractive where ducting is impractical. Their limits are real: the filter must match the specific chemical inventory, and institutions typically require environmental health and safety approval before installation — Penn EHRS, for example, states that ductless/filtering hoods must be approved before installation. That requirement exists because a filter rated for one chemistry can be useless for another: carbon beds adsorb some vapors well and others poorly, they saturate over time, and breakthrough happens without warning on the wrong chemical.
The decision rule is conservative: ductless only for a fixed, low-hazard chemical list that the filtration demonstrably covers; corrosive, high-hazard, or unknown mixtures stay ducted. If you cannot list every chemical the hood will see, plan for a ducted system. The ductless decision also has a monitoring component — filter saturation has to be tracked, not assumed — which is an operating commitment as much as a design choice.
Fire ratings and specialist review
NFPA 45, the National Fire Protection Association standard for fire protection in laboratories, sets the fire-conscious frame for exhaust ductwork, and it governs more than the duct: hood placement and room fire separation sit in the same standard. The general expectation is noncombustible duct construction, with non-metallic exceptions allowed when the material meets flame-spread and smoke-developed limits — commonly flame-spread index of 25 or less and smoke development of 50 or less per the ASTM E84 test method. What that means for a project is a question for the authority having jurisdiction, not a material page: confirm the required fire classification before selecting any plastic grade, and remember that flame-retardant grades reduce flammability without making a material noncombustible.
Fan selection, pressure drop, supply air, and air-change requirements (6 air changes per hour is a common minimum for hood rooms) sit outside a duct-material article. Give your engineer the airflow and chemical list from earlier sections; the engineer turns them into a fan, a control scheme, and a balanced system. The same boundary applies to the controls: a VAV system that holds face velocity as the sash moves is a design choice the engineer makes from the airflow numbers this page helps you produce, not a number this page can hand you.
Decision point: after this module you know when ductless is off the table and which design decisions you must hand to the engineer instead of deciding yourself.
Worked Example: Sizing a Fume Hood Exhaust Duct
Walk one concrete case through the chain. A teaching lab installs a 4 ft chemical fume hood with a 3 ft wide opening and an 18 in (1.5 ft) operating sash. The lab plans acid and base work at ambient temperature.
1. Face velocity. Target 100 FPM (0.5 m/s), consistent with the 80–120 FPM acceptance window.
2. Airflow. Open area = 3 ft × 1.5 ft = 4.5 ft²; Q = 100 FPM × 4.5 ft² = 450 CFM.
3. Duct velocity. Choose 1,500 FPM, inside the 1,000–2,000 FPM screening band.
4. Round size. A = Q / V = 450 / 1,500 = 0.3 ft²; D = √(4A/π) = 7.4 in.
5. Standard size. The 200 mm PP duct covers the 7.4 in case; the φ20–600 mm family has the size, and the square version (a 200 × 200 mm section with equivalent diameter near 200 mm) tucks along the wall if headroom is tight.
6. Material. Acid and base media at ambient temperature sit inside PP’s band, so PP is the candidate; continuous welded seams for the corrosive stream, flanged where disassembly is needed.
Scale the example and the outputs scale with it. Two hoods on one manifold at the same conditions double the airflow to about 900 CFM, which at 1,500 FPM needs a round duct near 10.5 in — the 250 mm or 315 mm PP size, depending on the family’s standard steps. Change the medium instead and the material moves: raise the acid service above roughly 90°C and CPVC or FRP takes over; add hydrofluoric acid and FRP with the resin confirmed against the chemical data sheet; make the exhaust solvent-heavy and 316 stainless steel becomes the defensible choice. The method stays the same — worst-case list first, then the matrix, then the sizing chain.
Before you order, sanity-check the result against the hood’s own data: a hood that draws 450 CFM at a 100 FPM average will feel the difference if the sash opens higher, because the face velocity drops unless the fan follows the sash. Constant-volume hoods hold the same airflow and accept a lower face velocity at full sash; VAV hoods adjust the flow to hold the face velocity. That control choice is the engineer’s, but it changes the number you hand to the duct manufacturer — state the sash position the airflow was calculated at.
The example also shows why the numbers stay screening-level. The 450 CFM figure feeds the duct size, but the fan that moves those 450 CFM has to overcome the friction of the actual run — elbows, transitions, and the cap all add resistance that a duct-size calculation does not include. Hand the engineer the airflow, the run length, the elbow count, and the chemical list; the engineer returns the fan and the final pressure numbers. The duct material and size from this page survive that handoff unchanged, because they depend on chemistry and airflow, not on the pressure calculation.
Decision point: after this module you have a complete worked chain to copy for your own numbers, and you know which parameter changes push you to a different material or size.
Selection Checklist: What to Send Your Engineer or Manufacturer
Take this list to the RFQ. Every row is an input the engineer or manufacturer needs to give you a defensible answer, and each one is something you can gather from the hood’s data plate, the chemical inventory, and the room layout — no design work required.
| Item | What to include |
|---|---|
| Chemical list | Each chemical, concentration, and temperature — the worst case wins |
| Hood inventory | Hood count, sash width, maximum sash opening |
| Airflow | Total CFM from face velocity × open area, with simultaneous-use factor |
| Duct velocity and size | Target FPM band and preferred duct diameter or square size |
| Run and installation | Length, number of elbows, roof location, condensate drain plan |
| Fire classification | Project requirement and any flame-spread or smoke limits |
| Supply air and controls | Makeup air plan, constant-volume or VAV, alarm requirements |
| Project details | Location, timeline, and drawings |
Why each row matters: the chemical list sets the material row of the matrix, because worst case wins; the hood inventory sets the airflow, because CFM comes from sash area times velocity; the airflow sets the duct size, because size comes from Q ÷ V; the run length and elbow count are what the engineer needs for pressure drop; the fire classification can overrule a plastic material choice; the supply air plan tells the engineer whether the room can feed the fan; and the project details turn a generic answer into a fabricated run with a schedule. A complete list gets a complete answer; a partial list gets a re-quote. When the parameters are fixed, confirming the dimensional side — standard size, wall thickness, and joint method — is where the laboratory square-duct product page and the exhaust duct family come in.
Decision point: after this module you can send a complete parameter set and get a size, a quote, and a fabrication plan back.
Next Steps: Confirming the Specification
The chain in this guide produces a specifiable answer — an airflow, a candidate material, a duct size and geometry, and an installation list — but it does not produce the final design. The next step is to confirm the three inputs that everything else depends on: the worst-case medium list with concentrations and temperatures, the total airflow with the simultaneous-use factor, and the fire classification the project requires. Those three inputs fix the material, the size, and the grade conversation, whether the engineer or the duct manufacturer carries it.
For a renovation, add the existing constraints: available chase space, the roof penetration location, and the distance from the hood to the fan. These are the details that turn a standard 200 mm run into a project-specific layout, and they are the inputs a manufacturer uses to flag interference before fabrication. Sizes above the standard range are fabricated from sheet and welded to the same corrosion resistance as the extruded sizes; wall thickness and grade are confirmed against the project quotation rather than assumed from a catalog.
The confirmation conversation follows a repeatable order. Start with the chemistry, because it fixes the material row of the matrix before anything else is worth discussing: a solvent-heavy exhaust changes the conversation immediately, a perchloric acid application changes it again, and an ambient acid/base list keeps PP as the default. Only after the material is bracketed does the dimensional conversation start — and that conversation is about standard sizes, wall thickness, and joint method, not about a one-off custom geometry. Keeping the order fixed prevents the most common error, which is negotiating duct size before the chemistry has decided the material.
When you hand the checklist to the engineer, you hand over the airflow and chemical inputs the fan and control design need. When you hand it to a duct manufacturer, you hand over the dimensional inputs the fabrication needs. The same three numbers serve both, which is why the checklist is the deliverable of this page: gather it once, and both the design and the fabrication can proceed from it. The engineer converts the airflow into a fan and a control scheme; the manufacturer converts the material and size into a fabricated run with joints, fittings, and a schedule. Neither conversation needs to be repeated for the other to start.
Two common follow-up questions deserve direct answers here. First, how much safety margin should the numbers carry? The screening values in this guide are already conservative — the 100 FPM target sits inside the 80–120 FPM acceptance window, and the 1,000–2,000 FPM duct band sits inside the wider 500–2,500 FPM engineering range — so the margin belongs in the project specification, not in inflating the duct one size beyond what the airflow requires. Second, can a plastic duct serve a fire-rated application at all? That depends on the authority having jurisdiction and the project’s flame-spread and smoke limits; the answer is decided per project, and the engineer should put it in writing before fabrication.
For the wider picture, the application guide places lab exhaust inside the full PP duct application map, the corrosive-fume selection guide deepens the chemical-resistance decision, the ventilation duct materials comparison shows where each material family sits, and the sizing guide covers the duct-velocity calculation method. Between this page and those, you have the chain from face velocity to a quoted laboratory fume hood exhaust duct.
Decision point: you can now decide what to gather and who to hand it to — confirm your airflow and chemical list with your engineer, and confirm the duct dimensions and joint method with the manufacturer before fabrication.
