Alitherm Heritage windows review

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Nick Dardalis

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Alitherm Heritage windows are the best-known and best-selling aluminium windows with a steel-look style. Designed by Smart Systems, the UK’s largest aluminium systems company, Alitherm Heritage windows were one of the first products in the steel-look market. This excellent suite of slim profiles re-creates steel-inspired windows. They are an excellent solution, whether as a replacement for dated windows or as part of a new extension.

With so many manufacturers making Alitherm Heritage windows and under several different brands, this review focuses on the core system rather than an individual or other branded version.

Alitherm Heritage windows explained

alitherm heritage windows in black fitted to london apartments
Smart Systems Alitherm Heritage Windows
alitherm heritage13

The most popular and diverse steel-look, heritage and art-deco windows remain the best because of their wide availability, excellent styling and comprehensive range.

Editor's Rating:


  • Excellent price point compared to steel
  • Wide availability
  • Matching bifolds and French Doors
  • Also has an interior aluminium range


  • Multiple manufacturers can mean inconsistent quality
  • Choose your supplier and installer carefully

Alitherm Heritage Windows have been providing solutions for new windows or replacing old steel windows well before this trend for Art-Deco, Industrial or Scandinavian-style windows and doors became popular. Some of the best-known and longest-established aluminium manufacturers have been making them for years when nobody would consider them for the home.

Initially intended for commercial buildings, warehouses, dockside properties and older buildings fitted with old steel windows, Alitherm Heritage windows have been the go-to product when replacing original metal windows isn’t necessary. At the same time, these windows provide a sympathetic replacement for steel windows meeting planning requirements and not spoiling the overall building aesthetics. Throughout London, especially with many buildings fitted with steel windows, Alitherm has enabled these to be modernised, coverted to dwellings or new offices.

Today Alitherm Heritage windows are the best known among residential windows in the steel look and their range of matching single or double doors are superb.

As a result of these outstanding aluminium windows, many manufacturers have taken on this system under their own brand. Sunflex Heritage, REAL Aluminium, Aluco Aluminium, and many others use this system. Others like Duration Windows in Essex have customised these windows to make them even slimmer and better.

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Available as fixed, side or top hung casement, tilt and turn and pivot windows or designed as floor-to-ceiling windows, Alitherm heritage come as a comprehensive collection. Many people will only know the basic residential windows, but there’s also a version styled like old steel windows using W20 profiles and these are some of the most widely used commercially.

Even listed buildings have been refurbished with this brand of steel-look windows, and many London Boroughs approve the product as well as the Home Counties and Wales.

Why Alitherm Heritage meets most window designs

alitherm heritage windows in a curved design to new build flats

With nearly 90 aluminium profiles available, these windows are exceptionally well-designed. Combining frame and vent profiles, accessories, adaptor profiles, cills, corner posts, mullions and transoms creates a versatile product.

Whether the intended windows in the steel look are for large or small, fitting into new build openings, timber or stone surrounds or replacing old plastic, wood or metal windows. The product provides a solution for most houses or architect’s requirements.

For typical window replacements, there’s a 70mm deep outer frame meaning these windows easily replace old PVCu and especially timber windows. There’s also a 47mm profile suitable for new openings or where fitted to stone or timber subframes. Then the frame sections extend out into different styles. Stepped, flat, extended width and many more options make these windows work with all existing openings and meeting the intended design.

You even get light outer frame solutions making these windows ideal for internal windows or where minimal sightlines are required with frame-to-glass lines of just 33mm with some profiles.

For the opening lights, many opening vent profiles give you flat, stepped, chamfered, beaded or tape-glazed, and of course, those styled like the W20 steel profiles. Mullions and transoms form not only a structural point for the window but also an aesthetic one. Again many different profiles offer large or small sightlines including built-in drips, just like original metal windows.

Finally, multiple bead profiles give you a contemporary or putty-like styling, square or angled and many other options. It’s a fully comprehensive system, accompanied by many different cills, corner posts, intermediate structural mullions and more.

Of course, these windows need to create the grid-like pattern of steel windows and multi-light styling. Here, Alitherm Heritage windows come with 25mm or 41mm glazing bars. The benefit of these is creating neat and consistent sightlines with both windows and doors with side panels.

How Alitherm creates period or contemporary windows

It’s probably the choice of window handles and accessories making these windows some of the best for getting traditionally styled windows.

The collection of hardware allows the creation of beautiful period windows. The handle and hardware options are substantial as is the styling.

So whether you’re looking to recreate the handles of classic steel windows, monkey-tail or pear drop handles, pressed bars and even peg-stays, Alitherm provides many options. And what you get is also affected by who you buy these windows from. In reality, some manufacturers provide better versions of these windows than others.

Hardware styling also comes in desirable period colours. Matt black, pewter, silver, polished chrome, antique brass, and more. Find these windows from a good supplier with the best options possible and you do get some spectacular-looking windows.

Specifications of Alitherm Heritage Windows

The entire Alitherm Heritage suite comes with thermally insulated frames and high-quality powder coated finishes.

Windows, depending on the glass option chosen, come with a B Window Energy rating In most cases, you’ll get glass units having a soft-coat low-emissivity coating, warm edge spacer bars and argon gas fill.  U-Values, again depending on the glass specification, are around 1.5Wm2K. These windows, therefore, meet Building Regulations for window energy efficiency.

These windows are well-designed, secure and weather-resistant. However, it’s worth clearing up some possible confusion around the security ratings. Many home improvement websites market PAS24, Document Q and Secured by Design. Therefore it’s easy to assume entire systems come with these security tests and certifications.

Alitherm is only tested using fixed and casement windows only. The multiple combinations of these windows and especially combined with steel-look doors mean your particular configuration hasn’t been security tested. Does this mean the windows are not secure? No – it just means there’s no official certification attached to them. It’s also worth pointing out that the door version of Alitherm has no security testing either (at the time of writing this article). As these are the most popular steel-look doors, consumers don’t see this as a factor in their buying decision. These products are all about style and design.

When it comes to colours, black is of course, the most popular, but Smart Systems paint their own profiles and offer some spectacular special colours in metallic and under their Smart’s Sensations textured and Alchemy anodised effect finishes. They’re fantastic in this style, giving a much more modern style than typical matt black colours.

Some of the best brands using Alitherm Heritage

As mentioned, many trade manufacturers use Alitherm Heritage and rebrand it as their own product. This is nothing to be worried about and it does not in any way mean you’re not getting an authentic window.

These manufacturers have identified how to improve the system and, in many cases, work with Smart Systems to do so. Prefix Systems, Customade Group, Duration Windows, Everglade Windows, Sunflex and Aluco Aluminium are probably the best known of these companies using the product either as standard or enhanced in some way by them.

Even if you go with the standard system, it’s great.

Other brands to consider with Alitherm Heritage windows

Here we’re concentrating on styling and products rather than price. The following products are a good comparison with Alitherm and some of the better steel-look windows.

Aluk Optio 58BW ST steel replacement

Similar in brand perception, the Aluk version of a steel look window. It doesn’t have the depth of profile options you get with Smarts, but the 58mm or 70mm frames make these just as good for new or replacement window projects. These come with a square, stepped edge or putty line styling too.

Aluk have a strong reputation for insulation and acoustic performance with their windows so you’ll get better energy efficiency with these windows compared to the Alitherm.

Reynaers SL38

We consider this the more premium offering for steel-look windows, and Reynaers has styling absolutely on point with their SL38 range. Their doors aren’t as stylish as the Alitherm version, but these are arguably the better option for windows.

Schuco AWS 70 ST Windows

With Reynaers, Schuco is one of the best aluminium brands, and they, too, offer a steel-styled version of their very well-priced AWS70 ST model.

These too come with the projecting bar of W20 steel profiles as well as other versions and are at the premium end of aluminium window systems.

airMOD Heritage

Everglade Windows have a great windows collection with the aïrMOD range and also fabricates steel-look glazing by Smarts. aïr MOD is authentic in styling and comes with several different window types and styling options. The heritage flush sash and tilt and turn models are especially noteworthy.

Decalu aluminium by Deceuninck

The Decalu aluminium windows from Deceuninck is quite recent with this PVCu systems company now branching out with Aluminium in the UK.

Decalu are a very good windows range marketed significantly with installer and manufacturer benefits rather than for the end-user. Decalu windows come in a similar style to Reynaers SL 38 with their Decalu 94 Retro and Decalu 110 Steel as well as the Decalu 88 New Steel versions. So on a styling comparison, these are also worth checking out but you might struggle to find these in showrooms right now.

Sheerline Classic aluminium windows

Sheerline is another new brand on the market and their range offers a stepped and flush stepped model that you could consider with the other brands we mention here.

The issue we have with Sheerline, as great as they are, is what in our view, will be a huge headache for existing or future homeowners once the windows are out of warranty or the property changes hands. The beadless design we see as something few double-glazing maintenance and repair companies are going to want to get involved with. No glazier wants to take an aluminium window apart!

Alitherm Heritage windows – summary and conclusion

Slim, stylish, well-designed and above all, established and tried and tested. Alitherm Heritage windows deliver on quality steel-look windows and come with arguably the best aluminium steel-look French doors. Smarts steel-look bifolds are probably the best styled too. There are better versions for use inside the home with single glazing and with improved features made by Aluco and other independent manufacturers.

The sizes of Alitherm don’t go as wide or tall as some other brands, but this isn’t an issue with many steel-look products going into standard-size openings.

However, for exterior windows hinged and folding doors, this is one system and brand to consider with the others.

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