DUCTWORK TURNS FULL CIRCLE

A designer’s guide to the benefits of selecting a circular ductwork system

A booklet produced by SCANDIACONSULT, Box 35, S-164 93 Kista, Swedenat the request of Lindab Ventilation AB.

Economical and technical aspects of the selection of duct systems

Traditionally, ventilation and air conditioning ducts have beenmanufactured with rectangular cross sections. The rectangular duct caneasily be adapted, e.g. to restricted ceiling voids and plant rooms,however, often at the cost of efficient airflow design and possible costsavings. A circular duct system normally performs better and offers amore economical solution, which is the reason why it always pays to studyand compare the ductwork design before selecting which type is to beused for a specific application.This booklet summarises various aspects found when ductwork systemsof different design are compared: Emphasis has been made to keep the presentation on a factual andobjective level. All research material has been documented and filed forreferral.In all cost comparisons made, the pre-sealed push-fit circular system hasbeen used.The current Scandinavian market prices have been used for allcalculations.

1. Circular ducts are more air-tight than rectangular

It is of utmost importance that the air within aventilation system is delivered to the designed outletpoints and that leakage through the duct system isminimised.The present Eurovent and the future CEN standardsdefine three leakage classes:

A: the lowest class. Leakage factor: 1.320 litres/(s,m2) at 400 Pa(= 0.260 cfm/sqft at 8.4 lb/sqft)

B: the medium class.Leakage factor: 0.440 litres/(s,m2) at 400 Pa(= 0.087 cfm/sqft at 8.4 lb/sqft)

C: the highest class.Leakage factor: 0.15 litres/(s,m2) at 400 Pa(= 0.029 cfm/sqft at 8.4 lb/sqft)

Class C is thus three times tighter than Class B andnine times tighter than Class A.It is far simpler and more economical to connectvarious parts of a circular duct system than that of arectangular:

– Connecting two circular spiral wound ducts onlyrequires one fitting, whereas rectangular ducts areconnected by use of a complete separate flangingsystem.

– The perimeter, that has to be sealed, is shorter ona circular duct:For the same free cross sectional area, a squareduct has 13% longer perimeter than the circularone, for a rectangular duct with side ratio 1:2, theperimeter is 20% longer, 1:3 30%, 1:4 41% and 1:551%.

Ducts with a high degree of air-tightness areincreasingly in demand for many reasons:

– Rising energy prices - the cost for filtering, heating,cooling and distributing air is rising rapidly.

– Good indoor air quality (IAQ) has to be guaranteedtoday. An increasing number of existing buildingsare being classified as "Sick Buildings". One of theremedies to this is to increase the amount of freshair intake. With circular "air-tight" ducts it is ofteneasier and more economical to fulfill theseincreasingly stricter demands.

Pressure Difference in Pa

Leakage classLeakage factor (l/s)/m2

2

Fig 1A rectangular duct 250 x 150 mm can, withoutany increase in pressure drop, be replaced by acircular duct of 200 mm diameter within the samespace.The in-situ cost for the circular duct isapproximately 50% of the cost for the rectangularduct.

Fig 2Flat rectangular ducts can often be replaced byseveral circular ducts without any need for extraspace.The in-situ cost is lower as shown in Fig 4The use of two or more circular ducts instead ofone rectangular gives beneficial advantages withbetter airflow control, simplified air balancing andmore flexible fire zone sectioning.

Fig 3Circular ducts are approved with thinner layers ofoutside fire insulation material than the equivalentrectangular ducts. Fire insulation of ventilation ducts, minimumdemands as specified by Swedish standards. Theouter temperature must not exeed 140°C duringthe time (15,30 or 60 minutes) the fire is ongoinginside of the duct with a fire curve as defined byISO 834.

InsulationType

InsulationThickness tmm

Outer Inner

∅ ∅

net mattingA15: sheet

3030

4030

–30

–30

net mattingA30: sheet

5050

7060

–50

–50

net mattingA60: sheet

100100

140120

–100

–100

2. The installation cost is lowerThe overall cost of a duct system built with circular ducts isdistinctly lower than one with rectangular ducts.The installation is simpler to carry out and the air tightnessproperties are better than when rectangular and flat oval ductsare used.One circular duct is always installed at a lower overall cost than arectangular of the same equivalent diameter. Fig. 1.Using two circular ducts instead of one rectangular also results ina lower overall cost. Fig 2. In some cases even several circular ducts can result in a lowercost when replacing one rectangular duct.

There are several reasons for the lower cost of the circularduct system:

– It consists of a limited number of standardised componentsand sizes.

– Manufacturing of the ducts and fittings is highly automatedand subject to advanced quality control.

– In some cases, the installation time for a circular duct systemis only a third of that for a similar rectangular system.

– The cost for insulating is lower due to several reasons such as:

– The amount of insulating material is reduced due to theshorter perimeter of the circular duct compared with therectangular one.

Circular ducts are in some markets approved with thinnerlayers of outside fire insulation than the equivalent rectangularducts. Fig 3. It is in all cases a fact that the same heat loss isachieved by using a thinner layer of insulation for circularducts than for rectangular.

It is more accessible and therefore easier to lag. Theattenuating properties of a circular system are superior duemainly to a higher degree of rigidity. See section 9.

– An example shows that a circular duct, Diam. 500 mm,requires approximately 13% less insulation material than theequivalent rectangular duct, 500 x 400 mm.

– The in-situ cost (inclusive of transportation, packaging, waste,etc.,) is considerably lower for circular ducts than forrectangular with the same equivalent diameter. As shown inFig 5-9.

– The number and dimensions of duct hangers is reduced. Thespace between two hangers is 2.5 m for a rectangular duct but3.0 m for a circular one, thus reducing the required number ofhangers and the cost and installation time needed by some20%.

– Circular ducts often result in an improved control of the air flowdistribution.

3

Fig 4 The In-situ cost (inclusive of transportation, packagingand waste), for ducts with the same equivalentdiameter.

In the bar chart the cost of, e.g. 3 ducts of ∅ 315 mmdiameter (used as shown in Fig 2), is compared to thatof a rectangular duct 1000 x 250 mm dimension.

One circular duct with the same equivalent diameteras the rectangular duct has been used as a base - thisis always the most economical alternative.

4

The drawings below, Fig 6 - 9, give circularalternatives to the rectangular system shown in Fig 5at the top. All systems are calculated for the flow of 0.5m3/s. The highest and lowest pressure drop is

shown for all systems as is the maximum velocity. To the right of each drawing the in-situ costs for thesystems are shown in relation to that of therectangular system.

Fig 6System B

Cost for B = 0.24 A

Fig 7System C

Cost for C = 0.27 A

Fig 5System A

Fig 8System D

Cost for D = 0.31 A

Fig 9System E

Cost for E = 0.50 A

5

Installation withRectangular DuctsFig 10System R

Installation with Circular DuktsFig 11System S

No. AirFlow(l/s)

DuctDim.(mm)

AirVeloc.(m/s)

Ductlgth(m)

Nos.off

PressureDropea.

tot.(Pa)

1 2,400 500x400 12.0 10.2 1 2.8 28.02A – 500x400 – – 1 – –

2B 2,400/1,200 500x400//400x300

12.0//10.0 – 2 – 45.0

3 1,200 400x300 10.0 9.8x2=19.6 2 2.8 27.44A – 400x300 – – 2 – –

4B 1,200/600 400x300//400x200

10.0//7..5 – 4 – 36.0

5 600 400x200 7.5 4.8x4=19.2 4 2.5 12.06A – 400x200 – – 4 – –

6B 600/300 400x200//250x200

7.5//6.0 – 8 – 9.0

7 300 250x200 6.0 4.0x8=32.0 8 2.0 8.0

Total Pressure Drop (Pa)Total Installation Cost: R

165.4

No. AirFlow(l/s)

DuctDim.(mm)

AirVeloc.(m/s)

Ductlgth(m)

Nos.off

PressureDropea.

tot.(Pa)

1 2 400 ∅ 500 12.2 9.6 1 2.2 21.1

2 2 400/1 200 ∅ 500/∅ 400 12.2/9.5 – 1 – 44.0

3 1 200 ∅ 400 9.5 9.3x2=18.6 2 1.9 17.7

4 1 200/600 ∅ 400/∅ 315 9.5/7.7 – 2 – 32.0

5 600 ∅ 315 7.7 4.4x4=17.6 4 1.9 8.4

6 600/300 ∅ 315/∅ 250 7.7/6.1 – 4 – 21.0

7 300 ∅ 250 6.1 4.2x8=33.6 8 1.6 6.7

Total Pressure Drop (Pa)Total Installation Cost: S=0.51 R

150.0

When the total air flow into a large room is to be suppliedequally through a number of supply air registers, thedesign shown in the two examples below results in thesame duct pressure drop through all the registers – the air

passes through the same duct length and through thesame number of bends on its way to each register. Alsohere, the cost is considerably lower and approximatelyhalved, when using circular ducts.

6

3. The delivery time is shorterCircular ducts and fittings are stock items and can bedelivered quickly which facilitates fast track buildingprogrammes.Due to standardisation of sizes, a comprehensiverange of fittings and ducts can be kept in stock. Theduct diameters for the standard sizes follow ageometrical progression of cross sectional area withan approximate increase of the diameter of 25% overeach step. The metric dimensions which are includedin the coming CEN standard are shown in the tablebelow.

NominalInternal

Diametermm

Perimeterarea per

metre lengthin m2

NominalInternal

Diametermm

Perimeterarea per

metre lengthin m2

63 0.198 500 1.57180 0.251 560 1.760

100 0.314 630 1.979125 0.393 710 2.229160 0.502 800 2.512200 0.628 900 2.826250 0.785 1000 3.142315 0.990 1120 3.517355 1.115 1250 3.927400 1.257 1400 4.400450 1.413 1600 5.030

Rectangular and flat oval ducts must always bemanufactured tailor made for every individualinstallation, the variations are here practically infiniteas both widths and heights vary, a bend can eitherturn around the flat or the high side, etc., thealternatives are thus too many to admit any batchproduction and automation of the manufacturingprocess.The circular ducts can easily be cut to exact length onsite and are thus much more flexible to alterations etc.The rectangular ducts have to be made exactly tomeasure, any site alteration and adjustment isimpossible and ducts of incorrect length have to bescrapped and replaced.

4. Less space is needed for the duct system

The space required for installing a circular duct is oftenless than that of a rectangular with similar pressuredrop since rectangular ducts are joined by slip jointspushed onto the standing-seam joints, fitted on theducts. Protrusions made by these flanges add to thespace needed.

As these slip joints cover the duct width, they requirean available space of the same order on either side ofthe duct.Often, when space is restricted, e.g. when ducts areinstalled above the false ceiling in an office corridor orin a duct shaft and the ducts are only accessible fromone side/end, severe problems arise due to theimpossibility of applying mastic or tape to the inwardsfacing joint sections.

This will not only raise the costs of the installation andprolong the time needed for the job, but also reducethe air-tightness qualities of the ducts.

Ducts with external fire insulation– comparisons between rectangular and circular ducts(Mineralwool covered with Aluminium foil)

Duct Peri-meter

Thickness(mm)

Insulation Material Volume(l/m duct)

Relative Installation costs(cost/meter duct)

Fire class Fire class Fire classA15 A30 A60 A15 A30 A60 A15 A30 A60

Circular Duct ∅ 250 .785 30 50 100 24 39 78

Relation Circular/Rectangular .87 .75 .71 .71 .67 .62 .62 .92 .85 .60

Rectangular Duct 250x200 .900 40 70 140 36 .63 126

Low HighMedium

20mm30 mm

40 mm

7

5. Air flow measurements made the easy way

It is easier to measure the air flow passing through acircular than a rectangular duct. There are many flowmeasurement units especially designed for circularducts available on the market.

Measuring BendMBU 90°

Flow Measuring UnitFMU

Blastgate DamperSKMU

With these accurate but inexpensive devices theventilation systems can be equipped with fixedmeasuring units, a low cost method which enablesregular check-ups or continuous monitoring. A decreasing air flow has often been found to be thereason for a sound building turning "sick" - A fact thathas been stressed on many air quality conferencesduring the last few years.Also when making site measurements for controlpurposes, the circular ducts are easier to work with.When using the classic Prandtl-method the circularduct, regardless of size, has to be measured throughtwo holes at right angles. The rectangular duct willhave to be measured through several test holes, thelarger the duct, the higher the number of holes forcollecting the data needed to get the same measuringaccuracy as for the circular duct.

6. Installation work, handling and transportation is simplified

The weight and bulk of a circular duct system is lessthan that of a rectangular, this influences the cost leveland makes it easier to install. One individual is able to install circular duct systemsup to diam. 200 single handed, whilst two people arealways needed to install rectangular of any size. For the same free cross sectional area the circularduct is not only less material consuming, due to itsshorter perimeter and simpler connections, but thesteel gauge can be reduced for the smaller and mostfrequently used duct dimensions due to the more rigidconstruction of a spiral wound circular duct.This is shown in the following Swedish standardspecification for spiral wound ducts BFS 1988:18,chapter 4:13 for new buildings:

Diameter mm0-80 (80)-160 (160)-315 (315)-800 (800)-1250

Thicknessmm 0,4 0,5 0,6 0,8 0,9

However the HVCA DW/142 specification for sheetmetal ductwork specifies the following gauges forspirally wound ducts:

Maximum diameter mm205 762 1020 1525

Thicknessmm 0,6 0,8 1,0 1,2

The complete weight for a typical system comprising anormal combination of straight ducts, bends anddiffusers, is between 30 and 40 % higher for arectangular system than for a circular duct system.

7. Pressure drop is reducedThe pressure drop for a typical system comprising anormal combination of straight ducts, bends, anddiffusers, is often lower for a circular duct system thanfor a rectangular.This will lead to higher operation costs for therectangular system, the required power from the fan isdirectly related to the pressure drop, and so also ofcourse to the consumed electric energy.

8. Inside cleaning of ductsSome investigations of ventilation systems in buildingsthat have been classified as sick have shown thatdust, fungus, etc., collected in supply and return airducts have added to the emission load and thus to thesick building problem. The need for clean supply airducts has been stressed on several internationalhealthy building conferences. New building regulationsin some countries, e.g. Sweden, also require regularinspection of the ductwork and internal cleaning whenneeded.The cleaning methods (dry or wet) and cleaning tools(rotating brushes connected to heavy duty vacuumcleaners) used for internal duct cleaning are easierand cheaper to apply to circular than to rectangularducts, due e.g. to the standard diameters of thecircular ducts.As per SIS 82 72 04

As per SIS 82 72 06

8

9. Flat ovalWhen limited ceiling void restricts the use of a circularduct system and a multiple system of circular ducts isimpractical, a flat oval duct system offers an interestingalternative.Flat oval ducts are manufactured from spirally woundcircular ducts which have been formed into an ellipticshape in specially designed machines. See fig 12.Some of the basic advantages of spirally woundcircular ductwork permeate through to the flat ovalsystem such as:

– More rigid than rectangular since it is manufacturedfrom the seamed spiral duct.

– Elliptic shape with round corners gives a lowercontact area for a given cross section thanrectangular resulting in superior air flow.

– The rigidity reduces reverberation and noisepenetration.

– The duct system is joined together with slip jointswithout any need for fitting and bolting separateflanges onto the ducts and fittings.

– An aesthetic appearance well suited for exposedapplications.

Compared with circular ducts, the flat oval showssome of the drawbacks which apply to the rectangularsystem such as:

– An endless variety of widths and heights whichmakes standardisation, batch production andex-stock deliveries impossible.

– The manufacturing is more labour intensive andskill demanding.

It is assumed that the total in-situ cost level isapproximately the same as fore rectangular.Fig 12

10. Silent spirals and noise problemsModern ductwork design incorporating high velocityvariable air volume (VAV) and constant air volume(CAV) systems have inherent features which areknown to present serious noise difficulties. In all cases it is low frequency noise which constitutes the most intractable problem since it easily breaksthrough the duct walls of rectangular cross-sectionedductwork into the ceiling.The problem with noise break-out can to a large extent be avoided by using circular ductwork which

is far stiffer than rectangular and hence reduces thelevel of penetration through the duct wall.Where the air flow requires a ductwork diameter toolarge to fit into the false ceiling area, several smallerdiameter ducts should be used or as second best, flatoval ducting, since in noise terms it is false economyto use the conventional rectangular type of ductworkresulting in noise problems at the commissioning stage.

11. Pre-sealed circular duct systems of push-fit type

Another great advantage with circular ductwork is thepossibility of manufacturing all fittings and componentsof push-fit type, a pre-sealed system that simplifiesinstallation and guaranties a low leakage system.Some of these systems such as LindabSafe, Lindab’sdouble gasketted system, have been available sincethe early seventies. This system is Type Approved,certificated and guaranteed to withstand leakage classC requirements, see test report in Fig 14, for allcomponents included.The high quality systems are provided with seals madefrom EPDM age resistant rubber which is imperviousto deterioration when inserted between duct and fittingwall outside of the airstream.Recommended air temperatures are -30°C to +100°Ccontinuously and -50°C to +120°C intermittently.Gaskets made from oil-resistant silicone rubber areused for higher temperatures.

ConstructionThe LindabSafe sealing gasket is designed in the formof a U-profile of homogeneous rubber. The rubbergasket is located in a groove at the end of the fittingand is securely attached by a steel band.Fig 13When the fitting is connected to the duct, the flange of

the U-shaped strip will be folded back. The gasket willthus be better able to withstand negative pressurethan positive, since negative pressure will tend topress the gasket lips harder against the inside of theduct. The system withstands positive pressure up to3000 Pa (300 mm WG) and negative pressure down to5000 Pa (500 mm WG).Under British and European standards, there is agreater tolerance range between duct and fitting as thediameters increase. In order to obtain the maximumseal for all dimensions, successively heavier rubbergaskets are used for increasing duct dimensions inaccordance with the group divisions in the table below.

9

The advantages the push-fit system has to offer are ofgreat importance mainly regarding installation time andsavings on commissioning and it has thereforereplaced the conventional slip joint system in countriessuch as Sweden, Denmark, Norway, Finland and isgradually spreading into other markets on theEuropean continent.

Leakage classification testAll ductwork and fittings fitted with the LindabSafesystem, are included in the type approval certificate ofleakage up to and including class C.The leakage factor in (l/s) /m2 gives the flow of air thatleaks out of or into the system in l/s relative to thesurface area of the ductwork in m2.

Totalpressureon test

Pa

Total systemleakageflowrate

l/s

Total systemleakagereceived(l/s)/m2

Maximumleakageclass C(l/s)/m2

Relationshipreceivedagainstclass C

%400 3.11 0.112 0.147 76.2600 3.94 0.140 0.192 72.9800 4.61 0.165 0.231 71.4

1000 5.16 0.184 0.267 68.91200 5.69 0.202 0.301 67.11400 6.19 0.222 0.333 66.71600 6.58 0.236 0.363 65.01800 6.94 0.249 0.392 63.52000 7.36 0.262 0.420 62.4

Uncertainty of flow measurement is within ± 3%.

Testing and classificationThe type approval certificate (Type approval no. 1358/88)was obtained by the National Testing Institute of Sweden, anindependent government testing authority, carrying out aleakage classification test on the LindabSafe system.The test was carried out in accordance with Eurovent2/2 (Air leakage rate in sheet metal air distributionsystems). The graph illustrated below shows the leakage limitsfor classification C along with the received leakagereadings of the test.

Figure 14 shows the components and the layout ofthe system tested, constructed entirely of LindabSafefittings, accessories and Lindab spirally woundducting. No other forms of sealing agent were used.The joint length of the system was 41.8 metres. Theperimeter area was calculated to be 27.9 m2.

Fig 14

Manufacturers assume responsibilityWhen a product has been certificated there is animportant shift of responsibility towards themanufacturer. When supplying pre-sealed ductwork onthe Scandinavian market, the specialist manufacturersguarantee the leakage performance of their tested andapproved products. Since the onus of product performance falls on themanufacturers, the contractors only have to install inaccordance with given recommendations to besafe-guarded against failure.

1 SRFA Flexible aluminium duct2 SRFG Flexible galvanized duct3 RCU Pressed concentric

reducer4 MF Female coupler5 BU Pressed bend 45°,

radius 1.0xd6 RCLU Elongated concentric

reducer7 SLU Sound attenuator 30058 SR Spiral duct9 PSDRUClean-out damper

10 BFU Segmented bend 90°, radius 1.0xd

11 TU Eccentric tee-piece 90° 12 NPEU Expandible connector13 EPF Female end cap14 NPU Male coupler15 TCU Concentric tee-piece 90°

16 DRU Regulating damper17 SNPU Male coupler for

flexible ducts18 SMF Female coupler for

flexible ducts19 RLU Eccentric elongated

reducer20 BSU Pressed bend 90°,

radius 1.5xd21 RU Eccentric short reducer22 ESU Male end cap23 BKCU 90° pressed bend with

clean-out section24 BU Pressed bend 90°

radius 1.0xd25 BU Pressed bend 15°

1.0xd26 KLU Constant flow unit27 PSUU 90° collar saddle

with gasket

10

12. StrengthCircular ducts are normally made from a 137 mmwide steel strip which is seamed and formed into aperfect circular cross section (see illustration bellow).The technique employed gives each duct a rigiditythat reduces the need of additional stiffeners.

Negative pressureIn installations in which pressure is very low in relationto the atmosphere, there is a risk that ventilation ductswill collapse. This phenomenon is known as bucklingand occurs whithout warning at the weakest point inthe system. The buckling spreads along the duct andas negative pressure increases it becomescompletely flattened. The weakest point is often a"transit dent" in the duct. The bar-chart shows themaximum negative pressure an undamaged spirallywound duct can withstand without collapsing.

Positive pressureThe risk of ventilation pipes bursting as a result ofpositive pressure is considerably less than that ofcollapse caused by low negative pressure. At a givenpositive pressure it is also probable there will beruptures in the joint between the ducts long before theduct splits apart at the seam. If however theconnections can be well fixed, the duct will burst alongthe seam. The bar-chart shows the maximum positivepressure an undamaged duct can withstand withoutbursting.

13. SummaryThe benefits of circular ductwork are many andinfluential which has caused and is causing changesto traditional work patterns throughout Europe.This can be illustrated by a study of the Scandinaviancountries where the following development has takenplace:

1.1960 and before

Ductwork contractors manufactured and installedall equipment in square and rectangular form.

2.1961 - 1970

Some specialist companies started batchproduction of circular ducts and fittings.The ductwork contractors started buying circularwhich they installed alongside the rectangularmade in their own work shops.

3.1971 - 1991

A total change of behaviour took place duringwhich specialist manufacturers intensified theirlevel of automation, research and development.

During this period the ductwork contractors startedsourcing more materials from specialist suppliersat lower cost than by producing in-house. Thecontractors gradually concentrated their resourceson installing standardised prefabricated itemswhich were readily available at short notice.

These changes were made possible through thecontractors’ ability to adapt their work patternsaround the system that provides the greatestcompetitive edge. Consulting Engineers changedtheir designs and specifications from tailor madedesign of specially constructed ductwork for everybuilding’s specific needs to designs built around astandardised concept.

An international comparison gives the followingpicture of the actual market share of circularductwork and the way this has developed:

% of total ductwork market

1960 1965 1970 1975 1980 1985 1990Scandinavia 5 15 40 60 70 80 85Germany 5 5 10 15 20 25 30France 5 10 20 30 40 50 60Great Britain 5 10 15 20 25 35 45

11

SWEDEN

Lindab Ventilation ABSE-269 82 BÅSTADTelephone +46 (0)431 85000Telefax +46 (0)431 85310e-mail ventilation@lindab.se

Lindab Nord ABBox 66,SE-936 21 BOLIDENTelephone +46 (0)910 580000Telefax +46 (0)910 581500e-mail nord@lindab.se

BELGIUM

Lindab n.v.Nazareth, IndustrieparkBegoniastraat 13aBE-9810 EKETelephone +32 9 385 5011Telefax +32 9 385 6062e-mail info@lindab.be

CZECH REPUBLIC

Lindab s.r.o.P.O. Box 52CZ-251 01 RICANY-JAZLOVICETelephone +420 323 627111Telefax +420 323 637463e-mail info@lindab.cz

DENMARK

Lindab A/S

VENTILATIONLangkaer 20Postboks 1071DK-6100 HADERSLEVTelephone +45 73 232323Telefax +45 7453 0159e-mail lindab@lindab.dk

ESTONIA

Lindab ASSaha-Loo tee 4EE-74114 JOELÄHTMEVALD, HARJU MK.Telephone + 372 6348 200Telefax + 372 6348 210e-mail lindab@lindab.ee

FINLAND

Oy Lindab AbJuvan Teollisuuskatu 3FI-02920 ESPOOTelephone +358 9 2534 4500Telefax +358 9 2534 4590e-mail lindab@lindab.fi

FRANCE

Lindab S.A.Parc d’ActivitésFR-01 120 MONTLUELTelephone +33 47806 3641Telefax +33 47806 3616

GERMANY

Lindab GmbHPostfach 1355DE-22935 BARGTEHEIDEDE-22941 BARGTEHEIDETelephone +49 4532 28590Telefax +49 4532 5666e-mail lindab@lindab.de

HUNGARY

Lindab Kft.Állomás. ut. 1/AHU-2051 BIATORBÁGYTelephone +36 23 531100Telefax +36 23 312011

ITALY

Lindab S.R.L.Via Pisa, 5-7IT-10088 VOLPIANO (TO)Telephone +39 011 9952099Telefax +39 011 9952499

LITHUANIA

Lindab AS atstovybéMokslininku g. 20 LT-2600 VILNIUSTel +370 2 729 729Fax +370 2 729 730Mobil tel +370 86 84806e-mail lindab@lindab.lt

NEDERLANDS

Lindab Door B.V.UtrechtPostbus 9025NL-3506 GA UTRECHTTel +31 346 217161Fax +31 346 217155

NORWAY

Lindab A/SPostboks 171 KalbakkenNO-0903 OSLOTelephone +47 22 803900Telefax +47 22 803903e-mail lindab@lindab.no

ROMANIA

Lindab SRLSoseaua de Centura, nr. 8 Stefanestii de JosRO-8246 - ILFOVTel +40 1 209 4 100, Fax +40 1 209 4 124

POLAND

Lindab Sp. z o.o.Sadowa, ul. Kolejowa 311PL-05-092 LOMIANKITelephone +48 22 7518890Telefax +48 22 7519667e-mail info@lindab.pl

SWITZERLAND

Spiro International S.A.Industriestraße 173CH-3178 BOESINGENTelephone +41 31 7403100Telefax +41 31 7403131e-mail info@spiro.ch

UNITED KINGDOM

Lindab LtdLongman Court, Sketty CloseBrackmillsGB-NORTHAMPTON NN4 7PLTelephone +44 1604 707610Telefax, +44 1604 707620e-mail sales@lindab.co.uk

USA

Lindab Inc.Two Stamford LandingStamford, CT 06902Telephone +1 203 325 4666Telefax + 1 203 325 2111e-mail info@lindabusa.com

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© 2002 Lindab AB (publ). is the registered trademark of Lindab AB. Patented, protected design. We reserve the right to make changes without prior notice.