01535 603909

Outdoor courtyard living
London townhouse period style aluminium French Doors - Industrial steel look

Exceptional quality with fast efficient service to London - supply only (supply & fit available on request)


Aluminium Steel Look Heritage French Doors installed in York

Yes it is Aluminium!

  • Aluminium that looks like steel
  • Approved replacement for listed buildings by many London council authorities
  • Ultra slim framework
  • A fraction of the cost of steel


Replicate the appearance of traditional steel doors from a bygone era with classic glazing bars and panel designs to create a vintage look.

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


Rated 5.0 out of 5 Myar Craig-Brown - London E18

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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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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Rated 5.0 out of 5 Nicholas Kitchen

...really helpful with all my technical queries, which helped make sure my orders were mm perfect and the doors all went in smoothly...
They look great - will do it all again in our next house!


Rated 5.0 out of 5 Dom B

Super customer service, they actually answer the phone and call back promptly if they’re not available... very helpful throughout with technical advice.


Read the full reviews and our other 5 star reviews left on Google


Marlin Windows On TV

Our fabulous Heritage Doors featured on
George Clarke’s Old House New Home (The Edwardian house in Golders Green London)
broadcast on Channel 4 in November 2018

Watch the full episode here or

Watch the 90 seconds programme highlights



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

"Really happy with those doors" says homeowner Lauren


For when you need modern, secure, thermally efficient doors without sacrificing the heritage and character of your traditional or period property.



Manufactured With Care in Yorkshire

Delivered With Care To You in London



This extremely versatile aluminium door system is an authentic and cost effective glazing solution ideally suitable for a wide range of applications including heritage, listed, retro refurbishment and Art Deco projects. Looks like steel.

With slim sight lines that create maximum glass areas the stepped frame profiles, glazing bar options and hardware choices offer a classic appearance with excellent thermal and operational performance.

Exclusive hardware and a dedicated window system with matching frame profiles is also available to compliment this door system.



Manufactured For You

Exceptional Quality with Fast Efficient Service

Get A Quote Today

Marlin Windows are the supplier of Alitherm Heritage Doors
For London.


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 heritage door
Alitherm steel replacement heritage 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 heritage double door
Alitherm steel replacement heritage 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

period crittal style steel look heritage bifolding doors



Combine retro steel style with modern strength and exceptional thermal performance

Read More

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 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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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.

Read More

View Our Featured Steel Replacement Projects:




Rated 5.0 out of 5 Mark Jones

"No other supplier we contacted could offer the same quality, value or look."


Read the rest of this review and our other 5 star reviews left on Google


Document Downloads

File Type Document Description Download Document
Adobe PDF Alitherm Heritage
Section identification Guide
Download (33.5 MB)
Adobe PDF Alitherm Series
Supply only – Guide to installation
Download (403kb)

Technical Specification


Product Type Doors
Material Aluminium Polyamide
Dual Colour
Thermally broken


Max width 900
max height 2100
Max weight 60
Thermal suitability ★★★★★
Min Glazing 24
Max glazing 32

Locking options


Building suitability

light duty

The Buyers Guide To French Doors

guide to how to aluminium french doors

Read our guide to buying french doors for your home

Replacing Windows In A Listed Building

Read our guide to replacing windows in listed buildings

Read our guide to listed building window replacement

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 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

need more reasons? click here

Get A Quote

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


Call 01535 603909