Alitherm Heritage Steel Replacement Windows
Slim aluminium windows designed to replace original steel
Alitherm Heritage is our steel replacement windows system for period, listed and conservation-area properties.
It is engineered as a very similar aluminium replacement for original steel casements, with slim proportions in a rust proof frame that holds its paint finish for 25 years. It suits Grade II listed façades, Edwardian and Georgian frontages, 1930s semis with failing steel casements, Art Deco properties, retro refurbishments and stone-mullioned openings.
If any of that sounds like your project, we’d like to talk about it.
✔ Typical 4-week lead time for supply only
✔ Made to measure
✔ 10-year manufacturer warranty
✔ Nationwide supply & delivery
✔ Regional survey & installation
✔ 25-year paint finish guarantee
✔ Cradle to Cradle Certified® Bronze
✔ Made in Keighley, delivered UK-wide
Request a Bespoke Quote | 01535 603909
Which heritage window is right for you?
We make two heritage window systems; each have their own unique benefits depending on your priorities and individual requirements.
The Alitherm Heritage window system is particularly well suited to period, listed and conservation-area properties where the shape of the opening, existing stonework or planning requirements call for a more tailored window solution.
Sheerline Classic heritage windows combine strong thermal and security performance, with WER A on double glazing and A+ on triple glazing, U-values down to 1.1 W/m²K, a Thermlock® multi-chamber thermal break and PAS 24 Secured by Design accreditation.
Alitherm Heritage for new builds and contemporary extensions is a versatile Smart system that can also be specified to meet demanding performance requirements, while offering different aesthetic, configuration and installation options.
The main considerations when selecting your heritage window are:
- Aesthetics
- Route to thermal compliance
- Trickle vent location
- Colour range
- System limits
However, the best way to fully understand the differences between our two heritage systems is to get in touch by phone. This way we can have a meaningful conversation to clearly explain in easy understandable terms how each system differs to work out the best solution for you.
What is Alitherm Heritage?
Alitherm Heritage is an aluminium window system designed by Smart Systems which we fabricate here in Keighley. Intended as a direct replacement for traditional steel windows, its slim profiles make it particularly suited to period properties, listed buildings and refurbishment projects where retaining the proportions of the original windows matters.
The system has a 47mm frame depth and typical sightlines of 33mm for a fixed window and 58mm for an opener. The aluminium profiles incorporate a polyamide thermal break that contributes towards thermal performance when combining with either double or triple glazing options. A Window Energy Rating (WER) of B with an overall U value of 1.5 W/m² is achieved using a specific 28mm double glazed unit or an overall U value of 1.4 W/m² is possible using 28mm triple glazing with Argon gas. If required, by using Krypton gas in our triple glazed option this can provide an overall U value of 1.2 W/m². All of our frame and glass combinations are designed to meet the requirements of Building Regulations Part L.
Aluminium frames won’t rust – also modern hardware and high specification glazing provide a practical upgrade over ageing single-glazed steel windows. Crucially for heritage projects, the slim profiles help retain the appearance and proportions of the original windows without introducing the heavier sightlines associated with many standard aluminium glazing systems.
Alitherm Heritage is the system we recommend most often for Grade II listed façades, conservation-area frontages, Art Deco properties and 1930s steel casement replacements, particularly where the shape of the opening, existing stonework or planning requirements make a conventional aluminium window unsuitable.
Alitherm Heritage windows: the full specification
| Specification | Details |
|---|---|
| Sightlines | 33mm fixed light and 58mm opening sash, with a 47mm frame depth |
| U-value – standard double glazing | 1.5 W/m²K overall, with a Window Energy Rating (WER) of B. U-values of 1.4 and 1.2 W/m²K are possible with certain 28mm triple-glazing options |
| Glazing unit | 28mm double or triple glazing, gasket glazed |
| Building Regulations | Part L compliant |
| Thermal technology | Polyamide thermal break throughout all profiles |
| Design configurations | Fixed lights, shaped windows, and side- and top-hung openers |
| Multi-part windows | Modular construction with a flush or feature drip bar, exclusive to Alitherm Heritage |
| Colours | Classic RAL colours, textured finishes, Alchemy range, and dual-colour finishes in any combination |
| Handles | Wide range of traditional and modern styles, with colour-matched, plated or living-finish options |
| Security | High-security multi-point locking, with PAS 24 accreditation available |
| Sustainability | Cradle to Cradle Certified® – Bronze level |
| Warranty | 10-year manufacturer warranty and 25-year system designer paint-finish guarantee |
| Lead time | Typically 4 weeks for supply only, although this can vary depending on season and project size |
“The whole journey has been an absolute pleasure, have already recommended your services to many friends“
Heritage steel windows, replaced in aluminium
Every Alitherm Heritage window is made to measure for the existing opening, making it particularly well suited to replacing original steel windows in period properties. Its slim sightlines help retain the proportions and character of the original window which can be especially important on listed buildings and in conservation areas.
Compared with many conventional aluminium window systems, Alitherm Heritage is specifically designed as a direct replacement for steel windows, combining slim proportions with modern thermal performance and low-maintenance aluminium construction.
Alitherm Heritage also provides a cost-effective alternative to traditional steel window systems, although the final price will depend on the size, configuration, glazing and finish. The aluminium is supplied with a durable polyester powder-coated paint finish so there is no need for the regular painting associated with traditional steel frames.
Heritage metal windows, made in aluminium
Our heritage windows are manufactured in aluminium, so you get the same appearance of metal with none of the upkeep compared to steel. Old metal window frames are usually past the point of repair by the time they come out, with decades of thick layered paint and rust underneath.
The appearance of the original steel – stepped profiles and slim sightlines, so the replacement looks as it should on a period elevation.
Rust proof – aluminium does not rust, so there is no staining below the opening
Windows that open – new hinges and stays throughout, so a metal frame window replacement opens and closes properly.
No repainting – the polyester powder coated paint finish is guaranteed for 25 years.
Colour to suit the elevation – single or dual colour, with an extensive range of handles available.
Listed buildings, conservation areas and period homes
Alitherm Heritage is an approved replacement for listed buildings, accepted for listed building and conservation area work by London Boroughs of Islington, Camden and Tower Hamlets, Watford Borough Council, Essex County Council and Leeds City Council as well as Cadw, the Welsh Government’s historic environment service.
named councils – “many council authorities” cannot go on the page]. ? Final approval always depends on your specific property and your local authority, and we’ll supply technical drawings to support your planning application.
We also have a free sample service so a physical corner section can be presented to a conservation officer for consideration before you commit. Call 01535 603909 and ask.
MARLIN WINDOWS ARE ACE. Such a great company to deal with on our house renovation and our Heritage steel windows and doors finished of our contemporary modern extention perfectly. Can highly recommend this company for their total professionalism, quality and excellent price. Wouldn’t hesitate to purchase from them again. Well worth a visit to their showroom.
Richard Wilkinson, Swinton
Why homeowners choose Marlin
We are a family business, and have been manufacturing aluminium windows and doors at our factory in Keighley since 2003. The business grew by applying the same quality standards and strict attention to detail gained from experience in aerospace engineering. All of the aluminium glazing products we provide are made by us, not bought in as finished units.
“The whole journey has been an absolute pleasure, have already recommended your services to many friends.” – Mr & Mrs Paxton, Skipton
“The Smart system trumps the steel-type systems on thermal performance and cost…”. Andrew Beevers, Ketton, Stamford
Every window comes with a 10-year manufacturer warranty and a 25-year paint finish guarantee.
Visit our Keighley showroom
Visit our Keighley showroom to see Alitherm Heritage windows up close and explore the UK’s largest selection of heritage and steel-look windows and doors on display. Compare frame profiles, sightlines, colours, finishes and handles side by side before deciding what’s right for your property.
Showroom appointments are available Monday to Friday, 9am–4:30pm, and Saturday, 8am–12 noon. Call 01535 603909 to book.
Helpful guides
IS ALUMINIUM A SUITABLE ALTERNATIVE FOR THE REPLACEMENT OF STEEL PRODUCTS?
Steel look Aluminium Windows, Doors and Internal Room Dividers and Doors look very similar to their Steel counterparts but offer several benefits of being Aluminium.
The benefits of modern, secure, thermally efficient aluminium windows with the heritage and character of traditional steel at a fraction of the cost.
Frequently Asked Questions
If you require any support, please don’t hesitate to review our FAQs below or drop us a message on our contact form here
Are Alitherm Heritage windows approved for listed buildings?
They have been accepted for listed building and conservation area projects by London Boroughs of Islington, Camden and Tower Hamlets, Watford Borough Council, Essex County Council and Leeds City Council as well as Cadw, the Welsh Government’s historic environment service. Final approval always depends on your specific property and your local authority. We’ll supply technical drawings to support your application, and a free sample to show the officer.
How do Alitherm Heritage windows compare with Sheerline Classic?
Alitherm Heritage is the best like-for-like replacement for an original steel frame and is particularly suited to fit between stone mullions, heads and cills. Sheerline Classic has a deeper frame and a slightly wider sightline. It offers a slim heritage appearance that is particularly suitable for more contemporary applications, especially for modern replacements. If the shape of the opening or the stonework is your main constraint, start with Alitherm Heritage. Still not sure? Call us and we’ll talk it through.
My frames are metal rather than steel. Are these still the right windows?
Almost certainly. Most metal windows in British period houses are steel and our metal replacement windows are made to the existing opening. Send us a photograph with your dimensions and we’ll confirm which system suits it the best.
Will they fit my existing stone mullions?
In most cases, yes. Alitherm Heritage’s slim profiles are particularly well suited to traditional stone-mullioned openings and every window is made to measure for the individual aperture. Send us your approximate dimensions and a photograph and we’ll confirm whether the system is suitable.
How energy efficient are they?
Alitherm Heritage carries a Window Energy Rating (WER) of B and an overall U-value of 1.5 W/m²K. The aluminium profiles are thermally broken and by using different glass specifications we can offer enhanced U values of 1.4 W/m²K and even 1.2 W/m²K if required, keeping the system totally inside the limitations of Part L of building regulations.
Are they secure?
Every window has high security multi-point locking as standard with an optional upgrade to Part Q, PAS 24.
Do you install, and do you cover my area?
We offer a full installation service across West Yorkshire, South Yorkshire, Greater Manchester, Merseyside, Lancashire, Derbyshire, Nottinghamshire, the East Riding of Yorkshire and Cheshire. For projects further afield, we supply Alitherm Heritage windows nationwide for installation by your own builder or window installer.
What do you need for a quotation, and how long will it take?
To quote accurately we need three things: approximate sizes, width by height; a rough layout or sketch; and the location of the project. Quotations usually come back within 24 hours, and larger projects take a little longer.
Ready to transform your home?
Get a made-to-measure quote for your Alitherm Heritage Windows today. Our team will guide you through sizes, styles and glazing options to find the perfect fit for your home.
Or call us on 01535 603909 to speak with our team.
Come and explore…
Aluminium Bi-fold Doors, Sliding Doors, Contemporary Glazing, Aluminium Heritage Windows and Traditional Steel Replacement Doors
