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System aluminium windows: what 'system' means and how to check it

A plain guide for homeowners, architects and builders comparing aluminium window quotes. It covers the parts that make a window a system and the test ratings AluK publishes, plus the documents to ask any fabricator for.
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THE SHORT ANSWER

A system window is designed and tested as one assembly, with published ratings

In short: system aluminium windows come from a supplier-engineered series where profiles, gaskets, drainage, hardware and any thermal break are designed and tested together, with published air, water and wind ratings. A basic section window is assembled from standard profiles, so its performance leans on the fabricator’s workmanship.
AluK describes its system windows as “designed, engineered, and tested as a complete solution”, with every component made to work together rather than adjusted on site. That is a manufacturer’s description. No Indian regulation defines a ‘system window’ category; it is a trade term. Our plain reading is this: a system is a named profile series with matched gaskets, hardware and accessories, backed by test data you can ask to see. If a supplier cannot name the series or show the data, you are not really buying a system.

System window vs basic section window

This is a comparison of documentation and design, not of who is a good fabricator. A skilled workshop can build a sound window from standard sections. The difference is what you can verify before you pay.
ItemSystem windowBasic section windowWhat to ask for
ProfilesNamed series with a technical sheet, e.g. SC140TTStandard sections chosen by the fabricatorSeries name and sheet
Thermal breakOffered as TT or IW versions; NI means non-insulatedDepends on the section boughtTT or NI, in writing
Gaskets and brushesSpecified for the series, e.g. central gasket on 56IWChosen by the fabricatorGasket material and position
DrainageDesigned into the frame and trackCut to the fabricator's practiceWeep-hole detail
HardwareMatched to the profile with stated sash loadsSourced separatelyBrand and load rating
Test ratingsAir, water and wind values published for the seriesRests on workmanship; ask if any test existsStandard and class named

Based on AluK's system versus fabricated windows article and AluK India technical pages. AluK's contrast is the manufacturer's view.

Six parts that make a window a system

When we explain a system at the showroom, we break it into the parts below. Each one can be named on a quote and checked against a technical sheet.
  • A tested profile series. AluK publishes named series such as SC45, SC95TT, SC140TT, S146LM Infineo, 56IW, 67IW and BSF70NI, each listing maximum sash size, sash load, glass thickness range and test classes.
  • Drainage. Sliding frames drain through weep holes and channels in the track. Flexible weep seals block air but let water out, and blocked drains are a common failure. AluK says its SC45 and SC40 tracks are wider with a deeper gutter.
  • Gaskets and brushes. SC140TT uses high-density polypropylene retention brushes with central water stripping; 56IW uses a central gasket. One Indian supplier names EPDM as the standard weather gasket and advises checking it sits fully in its groove.
  • Thermal break. Two aluminium shells joined by a non-conductive polyamide strip. Not every system has one: the SC140NI frame lists Uf 7 W/m2K against Uf 3.5 for SC140TT.
  • Matched hardware. Rollers and locks are specified with the profile: stainless-steel double-wheel rollers on Infineo, die-cast rollers with polyamide wheels and ball bearings on SC140TT, multi-point locking on several series.
  • Tested ratings. Air, water and wind values with the standard named, plus cycle tests. AluK tests Infineo and SC40 to 25,000 operating cycles, which it equates to about 15 years of regular use.

PUBLISHED VALUES

What AluK publishes for selected series

Values below are copied from AluK India technical pages and are manufacturer-stated. Where two AluK pages disagree, we leave the figure out. Ask for the technical sheet that matches your size and glass before relying on any number.

See also: how to choose a window maker and tilt and turn windows.

SeriesTypePublished valuesNote
Infineo S146LMSliding, thermally broken or not21 mm interlock; standard sash 3000 x 3500 mm; 350 or 450 kg per sash; glass up to 32 mm; air Class 4 (600 Pa)Water and wind figures differ between AluK pages
SC140TTSliding and lift and slide, thermal breakUp to 400 kg per sash with trolley; glass 10 to 40 mm; Uw 1.7 double, 1.2 triple; AWW 4 / 8A / A4SC140NI is the non-insulated version
C87K-CS NIInfineo casement, non-insulated65 mm profiles; hidden sash; air 600 Pa (ASTM E283); water 750 Pa (ASTM E331); wind 3000 Pa (ASTM E330)Same values on AluK Home
67IWCasement, thermal breakUw 1.4 double, 1.1 triple; AWW 4 / E1200 / C5; RC2 burglary classTilt-turn option
56IWCasement, thermal breakUw 1.7 double, 1.2 triple; AWW 4 / 8A / A4; 46 dB with 66.2a/20/44.1a glassTest standard for dB not stated

Sources: in.aluk.com product pages for S146LM, SC140TT, C87K-CS NI, 67IW and 56IW; infineo.aluk.com. AWW = air, water, wind classes as AluK lists them.

What the air, water and wind numbers mean

Most ratings on an aluminium window sheet come from three tests. ASTM E283 measures air leakage through a window under a set pressure difference; a lower rate means a tighter window. ASTM E331 sprays water on the outside face while holding a pressure difference, which imitates wind-driven rain. ASTM E330 loads the window with uniform static pressure to simulate wind. The European route uses EN 1026, EN 1027 and EN 12211 as tests and turns the results into classes under EN 12207 (air), EN 12208 (water) and EN 12210 (wind).
AluK shows both kinds, for example air Class 4 (600 Pa) or water 8A. EN classes are European classifications, not Indian certification. In India, IS 1948:2024 replaced IS 1948:1961 and IS 1949:1961 in June 2024 as the specification for aluminium framed doors, windows and sliders, and wind loads for design are set under IS 875 (Part 3). Ask any supplier which of these their product has been tested or certified against, and for the document that shows it. For monsoon exposure, the water figure and the drainage detail are the two to read first; our guide to windows for heavy monsoon rain explains why.

One series name can mean two different products

AluK sells many series in both thermally broken and non-insulated form. TT and IW in a name signal a thermal break; NI means non-insulated. A quote that says only ‘SC140’ could be either, with frame values of Uf 3.5 or Uf 7. Our thermal break guide explains when the break earns its cost and when a non-insulated frame is a fair choice.
Glass is specified with the system, not after it. The series sets the glass thickness it can hold, from 10 to 40 mm on SC140TT, and the hardware sets the weight it can carry. A heavy laminated or double-glazed unit chosen for sun or noise reduction has to fit both. The window glass guide covers build-ups such as 6 + 12 + 6.

SYSTEM VS BASIC SECTION

What a system changes compared with site-assembled windows

AluK’s own article contrasts system windows with windows made by local vendors from standard sections and assembled on site, where sealing, performance and durability depend heavily on workmanship. That is a fair description of risk, not a verdict on every workshop. A careful fabricator can build a good window. What changes with a system is repeatability and paperwork: the same profile, gasket, drainage and hardware combination that was tested is the one installed, and there is a sheet to check it against.
AluK sells in India through certified partners who fabricate and install. We are an AluK Home partner, and fabrication for our projects is carried out by certified AluK Home partners. You can see the AluK systems we offer, including the lift and slide system and aluminium casement windows, before comparing. The aluminium versus uPVC guide covers the material question that often comes first.

How to ask any fabricator for system evidence

Name the series and version

Ask for the profile series name, the TT, IW or NI version, and the technical sheet for it. If the answer is a generic description such as heavy section, ask what that means in millimetres and kilograms per sash.

Ask for test values with the standard

Ask for air, water and wind values with the test standard named, ASTM or EN, and the glass and size they apply to. A number without a standard cannot be compared with another quote.

Check drainage and seals on a sample

Look for weep holes along the bottom track and gaskets seated fully in their grooves. One Indian supplier also suggests a torch test in a dark room to spot light leaking at the seals.

Get the hardware and paperwork in writing

Ask for hardware brand, roller load rating and cycle test, then who fabricates, who installs and the written warranty terms. Vague answers here usually mean the window has not been documented as a system.

FAQ

System aluminium window questions

Direct answers, with the limits stated.
Windows built from a supplier-engineered series in which the profiles, gaskets, drainage, hardware and locking are designed and tested together, with published ratings for air, water and wind. The series has a name and a technical sheet. AluK describes its system windows as engineered and tested as a complete solution before installation, rather than adjusted to fit on site.
Normal aluminium windows are usually assembled by a fabricator from standard sections, so sealing and durability depend more on workmanship. System windows add tested component combinations and published data. A good fabricator can still deliver a sound window. Either way, check the datasheet, the glass build-up and who installs it before you compare prices.
Usually they are quoted higher than basic sections, because the profiles, gaskets and hardware are engineered and tested together, and thermally broken versions cost more again. AluK warns that cheap windows tend to cut corners on materials, sealing and hardware. Ask for an itemised quote so you can see where the difference sits, and see our price guide.
Any window can leak if drainage is blocked or the wall joint is poorly sealed. A system gives you a tested water rating to start from; AluK’s Infineo page lists water Class 9A (600 Pa), though another AluK page gives 450 Pa. After that, clear weep holes, correct sill falls and a sealed perimeter decide the result.
No. It is a trade term, not a regulated class. IS 1948:2024 is the current Indian specification for aluminium framed doors, windows and sliders. Ask each supplier which standards their product has been tested or certified against, and for the document that shows it, rather than relying on the word system.
No. AluK offers many series in thermally broken (TT or IW) and non-insulated (NI) versions, and some lines, such as the C87K-CS NI casement and BSF70NI folding door, are listed as non-insulated. Check the version suffix on the quote and the matching technical sheet.
Ask for the series name and version, the technical sheet, test values with the standard named, the glass build-up and the hardware load rating. Then operate a full-size sample. Our Belagavi showroom has working sliding, folding and casement systems, and you can request a quote with your opening sizes.

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Visit the AluK Home Experience Center in Tilakwadi, Belagavi, or call +91 89704 69999 with your drawings, and we will go through the series, version and ratings with you.
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