The Frontage That Cost the Scheme Its Openings
A podium deck under six storeys of flats, two long elevations, and a mechanical drawing that showed a couple of grilles and nothing else. One elevation was against a retained cut and had never been going to open. The other faced the high street, and by the time the mechanical package was let, the client had sold that frontage as four retail units with solid shopfronts. Nobody had done anything wrong. The deck simply no longer had two faces that opened, and one face is not two opposing faces.
That single commercial decision converted a naturally ventilated car park into an enclosed one, and an enclosed car park carries a mechanical extract, fire-rated ductwork or a modelled impulse scheme, fans classified to keep turning in hot gas, duplicated power supplies, a cause-and-effect matrix and a witnessed commissioning day. None of it was in the cost plan, because on the day the cost plan was written the openings existed.
The decision is arithmetic and there is not much of it: perimeter wall area or floor area by level, how much of it is permanently open, and where that open area sits. What follows takes it in the order it actually gets made — the two duties the deck owes, how the openings are counted, how a mechanical rate is derived and in which units it arrives, what temperature does to a volumetric duty, and what proves any of it on the day.
Two Duties Sharing One Set of Fans
A covered car park owes two separate ventilation duties, and they get confused constantly because on most schemes the same fans serve both. Contaminant ventilation runs every day and keeps carbon monoxide and nitrogen dioxide down in a space people walk through with an engine running beside them; the criteria are exposure limits rather than airflows, and in the United Kingdom they trace to Approved Document F and to the workplace exposure limits in HSE EH40 rather than to the fire guidance. Smoke ventilation runs once, for as long as the fire service needs the deck, and its criteria come from the fire strategy.
Confusing them costs money in both directions. A fan selected on the contaminant duty and then labelled as the smoke fan is not classified to survive hot gas, and its motor is very probably sitting in the airstream. A scheme sized on the fire duty alone runs a ten-air-change extract around the clock, the electricity bill arrives, and somebody switches it to hand-off. Put both duties on the schedule against the mode each belongs to, let the fan selection satisfy the larger one and the control strategy satisfy the smaller.
| What differs | Contaminant ventilation | Smoke ventilation |
|---|---|---|
| What sets the rate | Exposure limits for CO and NO2 in the occupied space, or a prescriptive air-change or floor-area rate | The fire scenario the approving authority has accepted, as an air-change rate, a volumetric rate at a stated temperature, or a modelled result |
| When it runs | Every day, on CO detection or a time schedule | Once, on a fire signal, for a stated duration |
| What it protects | People walking between the lift lobby and their car | Escape routes, and the firefighters who have to reach the seat of the fire |
| What the plant must survive | Ambient air, damp in winter, for the life of the building | Gas at a classified temperature for a classified duration, on a supply that survives the same fire |
| How it is proved | Airflow measurement and a detector calibration | Witnessed changeover, measured extract at fire speed, and on many schemes a hot smoke test |
Counting the Openings Before Anyone Orders a Fan
Two documents in common use ask the same question with different denominators, and mixing them up is the most frequent error on this page of the design. Approved Document B expresses the natural ventilation of a car park as a fraction of the FLOOR area at each level: openings amounting to a twentieth of that floor area, at least half of them in two opposing walls, for a car park to be treated as open-sided, and a fortieth on the same distribution basis for a naturally ventilated car park that is not. The International Building Code's open parking garage provisions express it as a percentage of the PERIMETER WALL area of each tier, paired with a minimum share of the perimeter length over which the openings have to be spread and a requirement that they be distributed over two or more sides. NFPA 88A, Standard for Parking Structures, carries its own definition again.
Take a percentage off the wrong denominator and the answer is not slightly wrong, it is wrong by whatever ratio the deck's floor area bears to its perimeter wall area, which on a wide shallow deck is an enormous number. Read the adopted edition of the adopted document, and write the denominator down beside the answer.
What counts as an opening is the second trap. Permanently open means permanently: a shutter, a security grille that closes at night, or a panel the tenant is entitled to glaze later is not an opening. A louvre is not the hole it sits in — its free area is a manufacturer-published figure for that blade profile and that pitch, usually a good deal less than half the structural opening, and it is the free area that goes into the sum. Mesh, bird guards, planting on the outside face, and decorative screening all take their share as well.
Distribution matters as much as area because the point of two opposing faces is to let wind cross the deck. A long deck with the whole of its opening area at the two ends can satisfy the arithmetic and still have a stagnant middle, and a fire engineer looking at the section will say so. Where the numbers pass and the geometry does not, the answer is usually a modelled scheme rather than an argument about the numbers.
Finally, defend the elevations. Openings that a fire strategy depends on are a permanent constraint on the building, not a drafting convention, and they need to appear as such on the planning drawings, in the sales pack and in the tenant fit-out guide. It costs nothing to write it down at design stage and it costs a mechanical extract scheme to discover it after a shopfront has been sold.
- Measure the perimeter wall area, or the floor area, of each parking level separately — tiers do not average, and one failing level fails alone.
- Mark only openings that are permanently open with no shutter, glazing or infill, and use the manufacturer's published free area for any louvre rather than the size of the structural opening.
- Deduct everything that will be built later against those walls: the retail liner, the substation, the cycle store, the plant room and the stair enclosure.
- Split the surviving area by elevation and test the distribution rule as well as the total, because a level can pass on area and fail on where the area sits.
- Run the lowest level first. It is normally the one that fails, and the scheme is designed for the level that fails rather than for the building's average.
The Rate, and Which Volume It Multiplies
Once the deck is enclosed, the rate arrives in one of two conventions depending on which side of the Atlantic the specification came from. The British convention is air changes per hour, and the guidance in Approved Document B for mechanically ventilated car parks is built around a normal-running rate and a higher rate for a fire, with the system arranged in two parts each capable of half the duty on an independent supply, the extract split between high and low level, fans able to keep running in hot gas for a stated period, and ductwork and fixings made of material with a high melting point. The numbers have moved between editions, so read the current one rather than the one in your last set of notes.
The North American convention is a rate per unit of FLOOR AREA rather than per unit of volume. The International Mechanical Code's enclosed parking garage provisions set a minimum mechanical ventilation rate in CFM per square foot, with a permitted reduction or intermittent operation where an approved automatic contaminant-monitoring system controls the fans, on conditions the section itself states. Where a rate is to be derived rather than taken prescriptively, the Enclosed Vehicular Facilities chapter of the ASHRAE Handbook — HVAC Applications is the reference that builds it from vehicle emissions and traffic patterns, and AS 1668.2 does the equivalent job in Australia and New Zealand.
The difference between the two is not cosmetic. A floor-area rate is blind to headroom; an air-change rate is not. Two decks with identical footprints, one at three metres clear and one at three point six, need the same fan under one convention and fans twenty per cent apart under the other. And an air-change rate raises a question the floor-area rate never asks: which volume? Gross to the underside of the slab, or to the underside of the downstands and the services? Deep beams create pockets that the extract will not reach, and counting those pockets into the volume inflates the fan while leaving the pockets unventilated. Settle the measurement basis with the approving authority in writing, early, and note it on the schedule beside the answer.
Air changes divide out cleanly only when the airflow and the volume share a unit system, so a fan schedule in CFM has to become cubic metres per hour before it will divide into a deck volume in cubic metres — do it branch by branch, because a total converted once hides which zone is short.
The airflow in cubic feet per minute for the unit or branch you are checking.
Airflow
2,039 m³/h
Converted using an exact defined factor of 1.69901079552 m³/h per CFM. Exact by definition — the m³/h figure inherits whatever the CFM figure was worth, including which fan speed or stage it was read at.
- Conversion factor applied
- 1.7 m³/h per CFM
They open the calculator with your figures already in it
CFM to Cubic Metres per Hour Calculator: 2,039 m³/h — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
Add the equipment this sizes
This result is a specification — 2,039 m³/h — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.
What this calculation does not cover
- Dividing the converted m³/h by room volume gives TOTAL air changes, which is not a ventilation rate. Most systems recirculate, and only the outdoor-air fraction dilutes anything — a unit reading 4.5 ACH on 10% fresh air is delivering 0.45 outdoor air changes an hour to the people in the room. Where a specification, an infection-control standard or a residential ventilation rule sets an ACH figure, establish which of the two it means before quoting the number this page produces against it.
- That same division assumes the room mixes perfectly, and rooms do not. Supply and extract terminals set close together in one ceiling zone short-circuit, so a share of the converted airflow returns to the unit without ever reaching the occupied zone, and dead corners sit well below the nominal figure whatever the total says. Tall spaces compound it, because the volume in the denominator includes a great deal of air nobody is breathing.
European, Middle Eastern and Asian fan, air handling and heat recovery data arrives in m³/h, so a job scheduled in CFM has to cross over before a unit can be selected or two submittals compared side by side. This page is for the mechanical contractor or plan reviewer doing that comparison. The gain specific to this direction is air changes: once the airflow reads in m³/h it divides straight into a room volume in cubic metres, and ACH falls out with no further arithmetic, where the CFM route needs a ×60 and a room measured in cubic feet. The trap is the neighbouring unit — a sheet quoting m³/min read as m³/h is out by sixty.
Hot Smoke Is Bigger Than Cold Air
A volumetric duty in a smoke system means nothing without the temperature it is stated at, and this is the single arithmetic difference between this job and every comfort ventilation job on the site. The same mass of air occupies nearly twice the volume at three hundred degrees Celsius as it does at twenty — five hundred and seventy-three kelvin against two hundred and ninety-three, a ratio a shade under two. A duct sized on the cold figure carries the fire duty at almost double the velocity it was drawn for, which is another way of saying it is about half the area it needed to be.
Fan classification is where this becomes a purchase order. BS EN 12101-3, the specification for powered smoke and heat exhaust ventilators, classifies a fan by a temperature paired with a duration; the classes commonly specified for a covered car park are three hundred degrees for sixty minutes, and four hundred degrees for two hours where the accepted fire is hotter. That classification is a tested property of one fan with its motor in one position, evidenced by a certificate, and it is not something a supplier can confer on a general ventilation fan by writing it on a quotation.
The second consequence catches people out in the opposite direction. A fan is a volume machine: it shifts roughly the same cubic metres per second whatever the density of what it is shifting, but the pressure it develops and the power it draws both fall away as the gas gets thinner. So the motor's worst case is the COLD condition, not the hot one, and a motor sized on the fire duty at temperature will trip its overload the first time somebody runs the system at fire speed on a cold morning to prove it works. Both conditions get checked and the schedule says which is which.
Velocity asks a different question in each mode. In fire mode it is a resistance question and nobody cares what it sounds like; in normal running it is a noise question, and on a podium deck with flats above it is the one that gets phoned in. The same duct carries the daily contaminant duty at a small fraction of the fire velocity, which is why a duct sized correctly for the fire case can be silent for twenty years and still be the right duct.
One extract point, part by part
- Classified extract fan — carries a tested temperature-and-duration classification with its motor in a stated position, and its motor is sized on the cold condition where the power draw is highest CFM to Cubic Metres per Hour Calculator
- Riser to discharge — the vertical route out of the deck, discharging where the plume cannot be drawn back into an inlet, a window or a balcony above
- Slab and downstand beams — the structural zone the duct competes with for clear height, and the downstands that trap smoke in pockets an extract point cannot reach
- Fire-rated casing — boards, joints, supports and penetration seals from one tested system, bought by the square metre off the same perimeter as the duct inside it Rectangular Sheet Metal Duct Surface Area Calculator
- Extract duct — sized on the fire duty at the temperature that duty is stated at, then checked again on the far gentler daily contaminant duty Duct Air Velocity Calculator
- Motorised smoke damper — selects which zone is being extracted and holds the others shut, which makes its wiring and its configuration a life-safety item rather than a controls detail
- High-level extract grille — passes its share of the zone duty through a published free area that is a good deal smaller than the hole it sits in, and it collects tyre rubber Return Air Grille Free Area Sizing Calculator
- Parking deck — the floor whose area drives one convention's rate and whose clear height drives the other's, and the surface the low-level extract sits just above
Run it twice on the same duct: once on the fire duty at the temperature that duty is quoted at, and once on the daily contaminant duty, because the first number sizes the metal and the second is the one the flats above will hear.
The volumetric airflow moving through the duct.
The internal cross-sectional area of the duct at the point being checked.
Duct air velocity
899 ft/min
Recommended velocity ranges vary by duct application (residential vs. commercial, trunk vs. branch) and are driven by noise, energy, and space constraints rather than a single code-mandated limit — compare your result against your project's design criteria or ASHRAE/SMACNA guidance for the specific duct type.
They open the calculator with your figures already in it
Duct Air Velocity Calculator: 899 ft/min — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
Add the equipment this sizes
This result is a specification — 899 ft/min — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.
What this calculation does not cover
- Airflow divided by area returns the average velocity across the whole opening, not the speed at any one point inside it — air runs faster down the centre of a duct than it does along the walls, so a single anemometer reading held mid-duct will sit above this figure.
- The relationship used is purely volumetric and carries no term for air density, so warm supply air, cold return air and the thinner air at altitude all report the same velocity while moving different masses of air past the same point.
- Whatever area you enter is treated as fully open. Internal insulation liner, duct board thickness and a balancing damper blade standing in that section all cut the free area, and because speed rises as area falls, the air squeezing past them is faster than the answer shown.
- Only the area reaches the arithmetic, never the proportions — a 20 by 8 duct and a 40 by 4 duct of identical square footage come back with exactly the same velocity. There is also no width-times-height helper on that field, so working the area out is yours to do and any slip in it carries straight into the velocity.
- The flow figure is entered once and held constant for the section being checked. Every takeoff upstream has already removed part of it, leakage removes more, and a blower on a lower speed tap or a loaded filter changes it again, so a long run has to be re-checked wherever the air it actually carries changes.
Where the Air Leaves, and Where It Has to Come Back In
Extract in a car park is conventionally split between high and low level, roughly half and half, with the low openings close to the floor. There is a reason for each half. The contaminant duty deals with exhaust gases that do not all obligingly rise, so an extract taken entirely off the ceiling leaves a layer at breathing height for a person bending into a boot. The fire duty wants the hot layer off the top. Take it all from one level and one of the two duties is being served by accident.
Every extract point is a grille, and a grille's gross size is not what passes air: blade material takes a substantial share of the face, and the free area is a manufacturer figure for that specific model rather than a rule of thumb. Access matters as much as area here. A car park grille collects tyre rubber, brake dust and litter, it sits high up over a parked car, and a progressively blocked grille is a capacity loss on a system nobody looks at between statutory tests.
Then the half of the balance that gets forgotten: air has to come back in. Extract without an inlet path is a partial vacuum — the fans ride up their curve, the measured flow comes in short of schedule, and the deck starts drawing make-up air through whatever route is left, which is usually the ramp or a stair door that then will not close against the pressure. Inlet openings, transfer openings between decks and the ramp itself are all part of the same sum, and inlet free area is worked out exactly as the extract grille's is. Where an inlet louvre sits in a wall shared with a residential lobby or a stair, it has to be a rated louvre with a damper, or the compartment line has simply been deleted.
The gross size a schedule quotes and the free area that actually passes air are two different numbers, so put the zone's share of the duty against the face velocity you can live with and the manufacturer's free-area percentage — and run it again for the inlet, which is sized the same way and priced by whoever forgot it.
The airflow the grille needs to pass.
The desired air velocity across the grille's gross face, chosen for acceptable noise and comfort.
The percentage of the grille's gross face that is actually open to airflow.
Required gross grille area
1.14 ft²
Free area percentage varies by grille model, blade spacing, and finish — use the specific grille manufacturer's published free-area rating for an accurate result, not an assumed typical value.
They open the calculator with your figures already in it
Return Air Grille Free Area Sizing Calculator: 1.14 ft² — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
What this calculation does not cover
- Returns an area, not a grille. You buy a catalogue face size in fixed increments, and free area does not hold constant as those dimensions change — a long narrow grille loses proportionally more of its face to frame and end margins than a square one of the same area, so the free-area percentage has to be re-read off the model actually selected once a size is picked.
- Face velocity is a stand-in for noise, not a measurement of it. What a grille sounds like at a given airflow comes from the manufacturer's tested NC data for that model, and a balancing damper mounted behind the core is a separate and usually louder source — a grille that meets the velocity target with a damper half closed can be the loudest thing in the room.
- Leaves out the pressure drop the return path actually sees. The grille's own loss is small; a filter behind it is not, and a filter-back return sized only for face velocity hands the blower a restriction that grows as the filter loads. Return paths are where systems quietly lose their airflow, and the governing number is the static pressure drop across the whole opening, filter included.
The Duct Has to Outlive the Fire It Is Emptying
A smoke extract duct is a compartment element that happens to carry air. It runs hot gas through spaces it must not ignite, under pressures a comfort duct never sees, and it is tested as such: BS EN 1366-8 covers smoke extraction ducts serving more than one compartment, BS EN 1366-9 covers single-compartment smoke extraction ducts, and the result is classified to BS EN 13501-4. A general ventilation duct with a fire damper at each compartment wall is a different assembly answering a different question, and it does not substitute for a classified smoke extraction duct however good the damper is.
In practice the classification arrives one of two ways: a proprietary duct system tested as self-supporting, or ordinary sheet metal boxed inside a tested board casing. Both are systems rather than materials. The duct, its joints, its supports, its hangers, the fixings into the soffit, the penetration seals and the access doors all come out of the same test evidence, and swapping a hanger for a cheaper one, or a board for a thinner one, invalidates the classification just as surely as leaving the casing off. The approving authority will ask for the test report and the field of application, not the brochure.
Both routes are measured off the same geometry — duct perimeter multiplied by run length — so the sheet metal and the casing are two separate line items taken off one dimension, with fittings, supports and penetrations counted by piece rather than by length. A take-off that lists the metal and assumes the casing is a percentage of it will be wrong by more than the contingency.
It returns perimeter times length for a straight run, which is the same geometry the board casing is measured on as well as the metal — so run it twice, and set the waste allowance from the casing system's own literature rather than leaving the sheet metal convention on it, or set it to zero here and add the boarding waste as its own line.
SettingsSettings for this calculation
The standard allowance most suppliers and estimating guides assume for ordinary work.
The duct's cross-sectional width (the wider side, by convention).
The duct's cross-sectional height (the narrower side, by convention).
The length of the straight duct run being fabricated.
An extra percentage of material added to cover seams, laps, and cutting waste.
Sheet metal surface area needed
167.9 ft²
- Base surface area (before waste)
- 152.63 ft²
They open the calculator with your figures already in it
Rectangular Sheet Metal Duct Surface Area Calculator: 168 ft² — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
Estimated cost — your price
This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.
What this calculation does not cover
- Returns area, not a metal order. Sheet gauge comes from the duct's larger dimension and its pressure class in the SMACNA construction tables, and it is the gauge that sets weight, price per square foot, and whether the sides oil-can at pressure. The same 15 m² is two very different purchases at 26 gauge and at 20 gauge.
- Excludes everything that holds the duct together and up. Transverse joint hardware (drive cleats, S-slips, TDC/TDF flange), stiffening angles on the larger sizes, and hanger strap and rod all scale with the number of joints and the hanger spacing, not with surface area — a long run made up in short sections carries far more of this than the area suggests.
- The dimensions entered are the metal size. An internally lined duct has to be made larger by twice the liner thickness on each axis to keep the free area the airflow was sized for, so entering the airflow dimensions on a lined duct buys metal for a duct that is undersized the moment the liner goes in.
The Scheme With No Ductwork At All
Impulse ventilation replaces most of the ductwork with momentum. A grid of small fans hung at the soffit pushes air along the deck toward a small number of main extract points, and the deck itself becomes the duct. The attraction is headroom: a ducted scheme takes depth out of a clear height the structural zone has already eaten into, on a deck whose clear height is fixed by the tallest vehicle it must accept, whereas an impulse fan hangs in the same plane as the lighting.
What you trade the ductwork for is a model. No prescriptive table sizes an impulse scheme. BS 7346-7 is the code of practice covering functional recommendations and calculation methods for smoke and heat control in covered car parks, and it is the frame; the fan count, the thrust, the spacing, the orientation and the position of the main extract come out of computational fluid dynamics run against a fire size and a design scenario. Agree the fire size, the scenario and the acceptance criteria with the approving authority BEFORE the model is run. A model run against assumptions nobody signed is an expensive way to start the conversation.
The model then has to respect a soffit somebody else is also using. Downstand beams block a jet; a beam deeper than the flow can duck under creates a stagnation pocket that shows up as a stubborn red patch in the results. Cores, ramps and stair enclosures do the same. Fan positions clash with sprinkler pipework, luminaires, signage, cameras and the swept path of a high-sided vehicle on the aisle beneath, and every one of those clashes moves a fan, and every fan that moves means the model is re-run. Coordinate the soffit before the model is finalised, not after.
Be clear about which job the scheme is doing, because impulse schemes are designed to at least two different criteria and the words are used loosely. Holding smoke back from an escape route is one objective; giving firefighters a tenable approach to the seat of the fire from a defined direction is another; clearing smoke after the fire is out is a third. They produce different fan layouts and different acceptance tests. The distinction belongs in the fire strategy document, in words, so that on commissioning day everyone in the room agrees what passing looks like.
Power, Signals and the Changeover Nobody Tests
Fire mode is a set of positions, not a speed. On the signal the fans go to fire duty, the dampers serving the affected zone open, the dampers serving every other zone stay shut, the contaminant control is overridden, the inlet path opens, and any interlock with a shutter or a barrier does whatever the strategy says it does. Every one of those is a device that can be correctly wired and incorrectly configured, and the difference between the two is invisible until somebody initiates a detector and watches.
The supply has to survive the fire the system is running in. BS EN 12101-10 covers power supplies for smoke and heat control systems; the cabling that feeds them is a fire-resisting cable, selected with its supports and fixings as a system and routed so it does not depend on the compartment it serves. Duplication is not the same as resilience: two fans fed from one contactor on one board are a single point of failure wearing the word standby. The two-part arrangement in the British car park guidance exists precisely so that a failure halves the extract instead of ending it, and it only does that if the two halves are genuinely independent back to the source.
Then the interface. Which device initiates fire mode — the fire alarm panel, a sprinkler flow switch, a detector in the deck itself? Which zone does that device select, and what happens if two zones go into alarm? Where does a firefighter find the manual control, and does it look like the panel they are trained on? These have one right answer per building, they live in the fire strategy and the cause-and-effect matrix, and where nobody has written them down they get answered on site by whoever is holding the laptop on the day.
Proving It on the Deck
Nothing here is accepted on assertion. Extract volume gets measured at fire speed — a traverse in a straight length of duct where there is one, or a summed set of readings at the grille faces where there is not — and it gets compared against the scheduled duty and against the volume the air-change figure was derived from, not against the fan's nameplate.
The cause-and-effect matrix is then run line by line, witnessed, with the fire alarm engineer, the controls engineer and the approving authority in the building at the same time. Initiate from each device in turn. Confirm the fans reach fire duty, confirm the correct dampers move and the others demonstrably do not, confirm the manual override works from where the fire service will stand, and confirm the system still performs with one supply isolated. This is where wiring and configuration errors surface, it takes a day, and it is the day that is always compressed when the programme slips.
Where performance was predicted by a model rather than taken from a prescriptive rate, several jurisdictions expect a physical demonstration on top of the measurements. AS 4391, Smoke management systems — Hot smoke test, is the published method for that and is used well beyond Australia; NFPA 92, Standard for Smoke Control Systems, sets the wider expectations for commissioning and periodic testing of smoke control systems. A cold smoke puffer proves that the fans run and the dampers open. It does not prove that a buoyant plume goes where the model said it would.
What Ages Out of a Scheme That Passed
Natural schemes fail by being built on. The louvre that provided a third of one elevation gets planted out; a tenant glazes a bay to make a showroom; the cycle store grows along the wall the openings were counted on. None of that goes through a fire engineer, and none of it looks like a change to the ventilation until someone re-runs the sum ten years later and finds the deck has quietly become enclosed.
Mechanical schemes fail more quietly still. Grilles silt up in a space that generates dust as a matter of course. A building management system gets replaced and the new one does not carry the fire-mode logic, because the fire-mode logic was in the old panel and not in the specification. Fire dampers seize in a position that happened to be right for the last test. This is a system that runs once, in the worst circumstances anyone in the building will ever face, and the only thing standing between it and that day is a periodic test that somebody has to be told, in writing, to keep doing.
What the decision actually needs on the table
Before a fan is selected, the scheme is either natural or mechanical, and that is settled by documents and measurements rather than by preference. This is what has to be assembled to settle it, and to hand over something a fire officer will accept.
- The adopted edition of the adopted fire and mechanical documents — The opening fractions and the ventilation rates have moved between editions, and the denominator differs between the British and the American test.
- Elevation drawings with every permanent opening marked and every future infill shown — Retail liners, substations and cycle stores are deducted before the sum, not after somebody notices them.
- Louvre and grille free-area data for the specific models proposed — Free area, never the structural opening or the nominal face size; the difference is often more than half.
- The fire strategy, with the fire size, the design scenario and the acceptance criteria written down — An impulse scheme cannot be modelled, let alone accepted, until these three are agreed rather than assumed.
- Fan classification certificates and duct fire-test evidence — The temperature-and-duration class for the fan, and the EN 1366-8 or EN 1366-9 report with its field of application for the duct.
- The cause-and-effect matrix, and a witnessed day in the programme to run it — Every initiating device, every damper position, every override, tested with one supply isolated and the authority present.
Opens the calculators above on one screen with the dimensions from this article already filled in. Quantities only — this site publishes no price list, because local prices vary too much to publish honestly.