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Aluminium that looks like steel.


Alitherm Heritage has been designed to offer a solution for heritage properties and building renovation projects where there is a need for a modern aluminium replacement for old steel.

Read our Buyers Guide: Alternatives To Steel Doors

Replace your old drafty steel doors with modern secure, thermally efficient aluminium steel replacements.

Replicate the appearance of traditional steel doors from a bygone quintessential Edwardian, Georgian or period style era with classic glazing bars and panel designs to create a vintage look.


Get 0% Interest Free Credit on Alitherm Heritage Doors

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Aluminium Steel Look Heritage French Doors installed in York

Key Features

  • Aluminium that looks like steel
  • Approved replacement for listed buildings by many council authorities
  • Ultra slim framework
  • A fraction of the cost of steel
  • Fully compliant with latest building regulations



Rated 5.0 out of 5 Myar Craig-Brown

I'd wholeheartedly recommend Marlin Windows. We ordered Steel Replacement French Patio doors and Windows. They are absolutely beautiful. And they were an absolute pleasure to deal with. Thanks Marlin!


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Product Information

The Smart Alitherm Heritage door is the ideal replacement for steel doors on heritage applications such as building renovations or apartment conversions.

The Alitherm Heritage door provides the solution for conservation areas where planning regulations require a like-for-like product replacement.

Alitherm steel replacement door
Alitherm steel replacement door profile

Alitherm Heritage door profiles feature the system's signature slim sightlines and elegant lines that complement Smart's existing Alitherm Heritage window and mimic those of steel doors.

The system has all the advantages of modern aluminium profiles that feature polyamide thermal breaks, allowing the system to achieve a Window Energy Rating of C (WER C) under the latest tougher June 2022 (Document L) building regulations when installed with our high specification double glazed unit.

Alitherm steel replacement double door
Alitherm steel replacement double door profile


Design Applications

Single or double external heritage doors
Balcony Doors
Open out or open in
Available with fixed side and top lights

Internal partition wall doors


Window Energy Rating of C (WER C)
Individual 24mm toughened double glazed units
Gasket glazed system
Multipoint locking with Avocet ABS cylinder
Traditional handle range and finishes
Made to measure design options

Visofold 6000 bifold doors lock

Premium Security Fitted As Standard With Patented Active Cam Technology

The clever locking system of the Avocet ABS® diamond grade cylinder knows when it has been snap attacked and fires into action to create a robust barrier to entry. The patented Active Cam TechnologyTM is hidden deep within a solid Molybdenum cam which is 20% stronger than steel, and delivers ultimate resistance against a lock snapping attack and snap/twist manipulation. All of the snap technology is focused on the outside part of the lock only. This makes sure that maximum strength is given to the inner part of the lock - the part that has the job of securing your door.

Visofold 6000 bifold doors secure by design



Rated 5.0 out of 5 Andrew Beevers

...trumps the steel-type systems on thermal performance and cost.
The grasp of the importance of design and quality of manufacture from the Marlin Team is second to none.


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internal crittal style steel look heritage partition doors



Interior glazing system for screens and room dividers using ultra slim aluminum steel-look framework.

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Rated 5.0 out of 5 Gareth Robinson

We used Marlin for windows and internal steel look doors and screens on our recent self build project.
Marlin are not local to us but provided an excellent service from quotation, advice, redesigns and with very detailed comms throughout.
The windows and doors are the talking point of our entire build. Adrian from Marlin said that windows become the eyes of the house and I didn't forget that - our eyes are simply stunning.
Would highly recommend.


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period crittal style steel look heritage bifolding doors



Combine retro steel style with modern strength and exceptional thermal performance

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Rated 5.0 out of 5 Dom B

From our initial contact with Marlin Windows we have been very impressed.
Super customer service, they actually answer the phone and call back promptly if they’re not available... very helpful throughout with technical advice.
The final products... look stunning.


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Technical advisors are on hand at the aluminium window and door showroom in Keighley in West Yorkshire

Unrivalled Quality Customer Service

Our high quality window and door products are backed by the same high quality customer service. Technical advisors are just a phone call away to answer all your questions no matter how technical.

Typical help provided includes:

  • Choosing the right product
  • Getting the right made to measure size
  • Help with ordering
  • Threshold advice

We provide a FREE sample service to assist with surveying decisions, design considerations, or planning applications – just pick up the phone and ask.

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Quality glazing backed by expert 5 star customer service


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Glazing and frame colour choice


Our aluminium profiles are polyester powder coated by our systems suppliers using the very latest paint application techniques guaranteed for 25 years.

Fully compliant to the latest June 2022 building regulations our standard double glazing is the exceptional light transmitting, energy saving ClimaGuard® A+ low emissivity (Low-E) glass manufactured by Guardian Glass.

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View Our Featured Steel Replacement Projects:


"Beautiful doors" - George Clarke (Channel 4 - George Clarke’s Old House New Home)


"Really happy with those doors" says homeowner Lauren


Document Downloads

File Type Document Description Download Document
Adobe PDF Alitherm Heritage Brochure
Download (11.3 MB)
Adobe PDF Alitherm Products
Download (5.6 MB)
Adobe PDF Alitherm Heritage
Section identification Guide
Download (33.5 MB)
Adobe PDF Alitherm Heritage
Product Data Sheet IMS123AH.201410
Download (508 KB)
Adobe PDF Alitherm Heritage
Supply only – Guide to installation
Download (403kb)

The Buyers Guide To French Doors

guide to how to aluminium french doors

Read our guide to buying french doors for your home

Alternatives To Steel - Buyers Guide

Read our guide to Crittall® window and door alternatives

Read our buyers guide to the best Alternatives To Steel Windows and Doors

Replacing Windows In A Listed Building

Read our guide to replacing windows in listed buildings

Read our guide to listed building window replacement

Replacing Windows In Conservation Area Properties

Read our guide to replacing windows in conservation area buildings

Read our guide to conservation area property window replacement


Why Choose Marlin Windows?

We care...

about the quality of finish
about you, your project and your property
about your 100% satisfaction

And we are rated ★★★★★ on Google

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"our builder said they were the best supplier and fitter they had ever used"
Mrs Nellist Haworth, Yorkshire


Call 01535 603909