Information about replacing Crittall Windows with aluminium.

If you live in a house with old Crittall® windows or other steel casements, what are the options replacing old metal windows with aluminium?  Is it also possible to improve your existing windows for better appearance, security and energy efficiency? In this article, we provide information on what to consider with steel window refurbishment and the aluminium options for replacing steel windows.

Products for the replacement of Steel Windows with aluminium.

replacing Crittall windows with aluminium
Aluminium steel-look windows made by Everglade Windows of Middlesex.

If you do want to explore the aluminium options for replacing Crittall® windows,  we have compiled a list of some of the window ranges for you to consider.  It is worth stressing that these are not really “Replacements” as you are not replacing like-for-like.  These aluminium windows and doors are designed to offer an alternative product.  Steel windows remain the best option, providing a different construction, slimmer sightlines and a significantly longer life.

Smart Systems Alitherm Heritage 47.

The Smart Systems Alitherm Heritage 47 is a remarkably well-designed aluminium window. This window suite creates steel look windows, New York Screens and even has a steel look door.

We have seen many installations using Smart Systems, and it looks great as a slimline aluminium window.  The door, in particular, is excellent for its visual similarity, although again not precisely like a steel door. There are several specialist manufacturers of Smarts Systems Alitherm Heritage 47, one of which is Everglade Windows in Middlesex, Pioneer Trading in Essex, Duration Windows in Canvey Island and other large or small manufacturers.

Smarts Alitherm Heritage.

Smart Systems also offer another steel look window to give similar aesthetics and an aluminium alternative to steel windows known as W20. Called Smarts Alitherm Heritage, this version is widely used in listed buildings, heritage properties and developments where a replica window is required. Alitherm Heritage is made in a modular form enabling any window design to be created using aluminium couplers. Authentic looking beads, drip bars and other profiles complete the look.

Smarts Alitherm Heritage comes as fixed, side or top hung casements, pivot windows and single or double sash windows.

It is worth mentioning that the Smarts Alitherm 600, used as conventional aluminium windows, also gets used in steel-look installations. If the profile sightlines and appearance work for your project, Alitherm 600 is worth considering.  Again we stress these are aluminium alternatives in a similar style, but nothing beats the authentic steel product.

AluK Optio 58BW ST steel replacement

The AluK Optio 58BW ST steel replacement window comes from another leading aluminium systems company.

The slimline profiles enable this window to be used in the home as well as commercially. AluK’s window is designed to replace old steel windows offering very slim sight lines and a credible aluminium alternative with high security and excellent thermal performance.

You can choose between 58mm or 70mm frame depths to suit new build and replacement applications. Other options include double glazed units up to 32mm, excellent security and a choice of what AluK calls Bay, Heritage or Contemporary profile appearance.

Finally, the AluK Option 58BW ST window comes as a fixed, multi-light, casement, bottom hung and multi-light arrangement.

Reynaers CS 24 -SL

Reynaers’ CS24-SL stands for Concept System 24 Steel Look. Windows are casement windows with handsome proportions and another suitable aluminium window to replace old steel windows.

The aesthetics centre around the external sight lines that include sloping glazing beads with a similar look found in old steel casements. The outer frames are only 19mm sight lines and the opening vent sections 31mm. The mullion and transom sections are also thin at just 13.9mm.

You can use the Reynaers CS 24-SL Steel Look window to replace old windows or for new build homes and extensions. They are also suitable for commercial buildings as well. Reynaers CS 24-SL are security and weather tested and even comes with a matching door option.

Reynaers Slim Line 38 aluminium window.

Also available from Reynaers is the SL38 suite of windows offering flexible design options as well as windows that can open in or out.

You have a choice of three different looks with the Reynaers SL38. There is Classic, Ferro and Cubic. Each of these is intended to offer a different visual look to a sliding aluminium window.

Classic offers a sloping detail to the outer frame and the opening sash. Cubic gives you a flat frame and sash. Ferro provides a flat external frame, but the sash features a projecting square nosing. All three are beautiful windows that are entirely different in appearance to the others we mention.

With the Reynaers SL 38, you get excellent weather performance, extensive colour choice, good U-Values and high security. Double and Triple Glazing is also available.

Also recently launched from Reynaers is the Slimline 68 aluminium window.  While not a steel look system, Reynaers SL68 offers very slim frames that would make it ideal for more basic window designs without the many horizontal bars found in metal windows. Reynaers are incredibly well-designed windows and should be checked out with other brands.

SAPA Crown 52mm casement.

While not marketed as a steel replacement window, the SAPA Systems Crown Suite of windows with the slimline vent and square outer frame is an option. We have seen these used very successfully to replace old steel windows, particularly those in hardwood subframes.

The SAPA suite offers a choice of vent, frame and mullion profiles making for a very flexible window to meet most design requirements.

Schuco Window AWS 70.HI

Schuco windows also come in many different styles and options including a slimline steel look window. A Schuco AWS70.HI is a highly insulated aluminium window that creates inward or outward opening windows.

There are four variants available in the Schuco suite such as the Soft Linen Residential Line and Steel Contour. You can mix and match the sections to create a custom window. However, the Steel Contour is the one intended for metal window replacements. It is suitable for new build openings as well. Face widths of the window are 117 mm.

Schuco ASS70 HI windows in steel contour are those specially designed for steel replacements. With the Schuco window, you can expect all the engineering found in their excellent sliding and folding doors. Schuco is also known for windows with low U-Values and excellent security test results too.

Schuco brings automation to their windows giving you a motorised opening option as well, called Schüco Tiptronic.

Replacing old steel windows.

If you can afford the luxury and the price premium, new steel windows are the way to go. New windows will retain much of the authenticity of your outgoing windows and steel specialists can advise, with many having an extensive range of products to choose from.

Is the sunshine bay available in Aluminium?

Crittall Bay Windows
Image courtesy of

If you have old steel windows with one or two curved glazed sides, you may be wondering if it possible to replicate these in aluminium? The answer is yes if your chosen supplier has the skills and the suppliers to do it.

Curving aluminium sections on elevation (to create curved head windows) is much easier than curving on plan such as sunshine bays. Bending the spacer bars that separate the outer and inner pane of a double glazed unit is easy for those with the knowledge and skills to do it. Curved glass is also possible, but you will pay the price for having all these standard sections sent to a specialist section bender.

What you need to do is seek out a specialist company that can create aluminium sunshine bay windows. You’ll find more suppliers of standard windows and fewer that offer curves and shapes. We can help put you in touch with these. The less experienced company will want your work but offer flat glass and angled bays using bay poles. If you wish to the curved window to match your original seek out a company that can do it.

Current Buildings Regulations are sympathetic to period windows.

If you live in a period property, one in a conservation area or with planning constraints, always check with your local Authority or Conservation Officer.

Many local authorities do make allowances for properties with traditional windows or those of historical importance or architectural significance. Always seek professional advice.

Consider fitting authentic Crittall® Windows.

It is worth extolling the virtues of these windows and just how good they are. The fact remains, that while there are excellent aluminium alternatives, steel windows, look different and are different.  Once again, if you want the 100% authentic product, check out the unique windows and doors by Crittall®.

Longevity, construction and appearance are just three great reasons also to consider a steel window.  Some windows are still working today more than 90 years after being fitted.  No aluminium or plastic product has this service life, nor is it likely they ever will.  Steel windows feature galvanised steel, durable finishes, quality hardware and are built to last. Steel windows are also the slimmest.

Steel remains a super durable material giving these windows excellent security even when they are as slimmer than aluminium. Choose a steel window today, and you will get all the style, energy efficiency and high security you associate with a new PVCu, aluminium or timber window. The only drawback to steel windows is their cost when compared to other materials. However, given how long they will last, it is an excellent investment in your home. As well as this, properties with authentic steel windows and also very desirable to prospective buyers.

A typical house with original steel windows.  Consider replacing them carefully.

Refurbishment of old steel windows.

One fantastic feature of old steel windows is how they work with the overall appearance of a house. Period homes are a favourite with homebuyers because of their character and original features. Windows are one of these. If you want to retain your original metal windows, refurbishment is one option. There are nationwide specialists in the restoration and renovation of steel windows, or you can seek advice and a suitable company from The Steel Windows Association.

Early generation steel windows will not be galvanised and probably worse for wear from corrosion; not helped by many different coats of paint over the years. The window hardware on original windows can be hard to replace if broken, and the putty may have failed as well. We suggest you seek advice from one of the specialists in restoration and get some initial advice.

In considering a repair to old steel windows, security and energy efficiency remain poor by modern standards. There is little you can do to improve it and this will be one compromise.

How can you repair old steel windows?

In deciding whether to repair or replace your old steel windows, your key concerns may be:

  • Improving Security.
  • Improving Energy Efficiency
  • Replacing your old single glass with double glazed units.
  • Reduction in noise levels
  • Improvement in weather resistance.

Depending upon the condition of the existing windows it may be possible to improve them in many of these areas. New seals, new handles, replacement glass and general refurbishment, are all offered by expert companies.

While you will not get the advantages of brand new thermally insulated windows, any good refurbishment provides some improvement over the old windows.

So what are your options for new windows in aluminium?

Secondary double glazing for steel windows.

It is worth mentioning Secondary Double Glazing. Secondary double glazing is an excellent alternative for houses with old metal or single glazed windows.  With secondary double glazing, you will usually find little resistance from conservation officers. Secondary double glazing is also substantially cheaper than new windows of any material.

Modern secondary double glazing is fitted behind original steel windows and is available in fixed, swing, lift-out and even sliding windows, meaning you should be able to retain the authentic look of your windows when viewed from the outside.

Conclusion and Next Steps.

It is worth mentioning finally that all of the above systems should work well if you need them fitting in stone mullions or hardwood subframes.

All of the above products will give you all the advantages of new double glazed windows that will improve your home over existing steel windows. For us, the Smart Systems Alitherm Heritage 47 and the Reynaers SL24 and SL38 are the more appealing aluminium window residentially.

Installers like Alitherm windows also having a matching Alitherm Door as a single or double door set. We provide some more information about steel look doors in aluminium.

There are other specialist independent companies whose business is aluminium steel replacements. Examples include the Heritage Window Company in London with their Benenden Range, Jennyfields in Hampshire with their great steel windows that also create sunshine bays.

What these companies often do is take an existing system like the Alitherm and tweak it. They work with the systems company to modify the profile to make it different from the standard product and frequently will get exclusivity to it. There’s nothing wrong with this way of creating a more bespoke window. Aluminium systems companies are in the business of selling bars of aluminium and if they can do this for an independent installer, they will.

If you would like more information about steel replacement windows, and where to see them, contact us today. We can help put you in touch with suppliers and installers and answer your questions about replacing Crittall windows with aluminium.

Crittall® is a registered trademark of Crittall Windows Limited and unconnected to the Aluminium Trade Supply Website.

Main image shows Smart Systems Alitherm Heritage 47 Windows manufactured and supplied by Everglade Windows in Middlesex

Published on November 27, 2017

Reader Interactions


  1. Katie says

    Fab artical. We are looking for aluminium crittall style windows and doors as we cannot afford the real deal, we are in Staffordshire. Could you recommend a supplier?

    • Nick Dardalis says

      Hello Katie, I’m not too sure in specifically in Staffordshire, however, if you get in touch with the below systems companies they should be able to help you.

      These three well-known systems all offer steel look windows and hopefully, they can put you in touch with a local installer. for the Alitherm Heritage Product for their SL38 and steel look system for their steel look window system.

      Sorry I can’t point you in the direction of a specific one at this time.
      Kind regards

  2. says


    Great info and website. Thank you

    We’ve just bought a 1930s deco property with half sunshine bays up and down. Looking for a good supplier and installer of curved Ali units in South East London.

    Original look needed!

    Thanks in advance


    • Nick Dardalis says

      Hello Paul, thank you for your enquiry and your kind comments. While many do the steel look windows, few are brave enough to attempt the sunshine bays, curving the aluminium on plan to achieve the right look.

      Ultimately a steel window will give you the most like-for-like replacement, however the below two companies also do then sunshine bays in aluminium.
      01252 757614
      10 Century Farm, Green Lane, Badshot Lea, Farnham, Surrey, GU9 9JH 

      Also The Heritage Window Company in Lewisham

      Hope this helps
      Kind regards

  3. Gina says

    Hello, we are renovating a 1950’s bungalow which currently has hideous UPVC windows. We would like Crittal style aluminium French doors at the rear and aluminium windows at the front (unsure if Crittal style or not).
    I’ve had a quote from Raynaers which is eyewateringly expensive.
    Can you advise if Smart Systems Heritage is comparably priced or cheaper/more expensive?

    Who would be a good brand but cheaper?

    Many thanks

    • Nick Dardalis says

      Hello Gina, thanks for your comment. Reynaers windows are excellent but check to see what products you’ve been quoted for as they do several ranges in their steel look windows. The Smart Systems Alitherm Heritage 47 system is excellent as a steel look door and window and is one of the most authentic looking products on the market as well. Another product to consider is the Aluk steel look window.

      The smart system is widely used for steel replacement products so you will be fine with this. Smart Systems is an excellent systems company and the biggest in the UK.

  4. Samantha says


    We live in Scarborough and really struggling to find a company that could provide and fit our home with Crittall style french doors, along with two windows and one single door …. can you help please??

    • Nick Dardalis says

      Hi Samantha, I don’t know anyone specifically in your area but they do exist! You’re looking for a supplier of the Smart Systems Alitherm Heritage 47 System as one example. If you go onto the Smart Systems website, in their find an installer put in your postcode, select windows and doors and that should bring up a list for you.

      Also worth getting hold of Aluk and ask who supplies their steel replacement window system in their area as well.

      Sorry I can’t be more specific with this one.

  5. Sarah Washington says

    Do you know if the sight lines are thinner with the reynaers 38 windows/doors or the smart alitherm heritage ones. Also which in your opinion looks better in real life. It’s so difficult to tell from the pictures which look more authentic. We were going to go for the smart heritage system, but having read your article and looked into the reynaers windows and doors the images look great on their website, so I’m in a dilemma!

    • Nick Dardalis says

      Hi Sarah, both windows are excellent and you should be happy with either. The Heritage System is arguably the better seller when it comes to steel replacement windows and doors. That said, Reynaers provides a bigger range of window profiles so it’s worth finding out about those too. We wrote about the product if you’ve not seen it

      The Classic and Ferro profiles look very good indeed.
      If you’d like to get in touch via the website, I can try put you in touch with both Smarts and Reynaers installers.
      Hope this helps, please don’t hesitate to get in touch if you’ve any questions or need further information. 
      Kind regards

  6. Lorna Swarbrigg says

    We are looking to put 3 large Crittel style windows into extenstions on an 1850’s property
    We are really confused about whether Aluminium or Steel is the better product and where to go to get the product we need. We live in Leeds
    Can you help?

    • Nick Dardalis says

      Hello Lorna,

      Both materials are fine but the authentic looking window remains the Crittall product. We are an aluminium website, but for the genuine article, Crittall® windows are fantastic.

      The reason aluminium windows in the steel style exist is purely price as steel is so expensive. Aluminium windows also won’t be as thin as steel either.

      So your choice is really down to aesthetics and cost.

      For aluminium, the below should be able to help you.

      Altitude Aluminium
      North West Head Office:
      Aviation Park
      Access House
      Flint Road
      Chester, CH4 0GZ
      01244 529 199
      0800 587 4068
      North West Bifolds
      12 Crucian Way
      L12 0AW

      For Steel, if you get in touch with Crittall Windows Directly they should be able to put you in the direction of a local installer. Alternatively the Steel Windows Association should be able to help you as well.

      Hope this helps, please don’t hesitate to get in touch if you’ve any further questions.
      Kind regards

  7. Nick Dardalis says

    Hello Meera, thanks for your kind comments. Yes the Smart Systems Alitherm product is excellent as a slimline and steel-look window, the doors look great as well. It is worth looking at the AluK ST system as well. That’s also very good. Here is a link to a company that’s used this product on the windows and Schuco system for the doors.

    Local to you I can suggest the below.
    0115 838 4747
    41 Evelyn Street
    NG9 2EU

    The Smart Systems Website can also point you to installers.

  8. Meera says

    Delighted to have found your website and this very informative article! I’m planning a renovation of my home in Nottingham and have my heart set on doors and windows that have the look of steel windows, but hopefully cost less while performing well. The Smarts Alitherm Heritage range looks like the perfect match. Can you recommend who I can contact in my region for costings and more information?

  9. M Radcliffe says

    Just a quick note regarding Jennyfields. In 2014 then replaced half of our Crittall steel windows with a very nice looking aluminium replacement set in hardwood frames.

    However, within 2 years of installation a number of the double glazed units were compromised and we got and still do get condensation inside the outer glass panel. We have also had loads of issues with rain water leaking in through the joins of the hardwood frames. Loads of photographic evidence to back this up and initially Jennyfields were quite proactive in rectifying the issues but I have had to chase them so many times in the last 12months I’ve had to send them a letter regarding breach of contract. We did have someone out recently but the work he has done has not stopped the rain water coming in!

    We are now in a position to replace the remainder of the windows in the house and we will not under any circumstances use Jennyfields to do the work. even if this means we are unable to completely match the windows. Shame.

  10. Emily says


    Thank you for such a great resource on aluminium glazing! A wealth of information end expertise.

    We are looking to replicate crittal as closely as possible for large French does and adjacent glazing, but actual Crittal is outside our budget.

    I wonder if you can recommend a local supplier or installer of The Smart Systems Alitherm Heritage 47 system in our area? We are based just outside Manchester City centre (chorlton-cum-hardy).

    Many thanks!

  11. Kim Dobson says


    After becoming increasingly confused about aluminium windows, your article is really helpful.

    I live in a 1930’s property. Which has original Crittall Windows, which need replacing. I love the simplicity of these windows and of course how slim they are. I have a lot of windows, small and large, as most rooms are dual aspect.

    I’d also like to turn a bay window into French doors.

    I live in Essex, and am very unsure of which window company would be best, and which quality product to choose. One of the local companies that supplies Crittall style replacements gets many very negative reviews.

    I love the style of the house and want to make sure I make the right choice. Crittall is just too expensive for me.

    I’d be grateful if you could point me in the right direction.

    Thank you.

  12. Kim Dobson says


    After becoming more and more confused about aluminium windows, your article is really helpful.

    I live in a 1930’s property. Which has original Crittall Windows, which need replacing. I love the simplicity of these windows and of course how slim they are. I have a lot of windows, small and large, as most rooms are dual aspect.

    I’d also like to turn a bay window into French doors.

    I live in Essex, and am very unsure of which window company would be best, and which quality product to choose. One of the local companies that supplies Crittall style replacements gets many very negative reviews.

    I love the style of the house and want to make sure I make the right choice. Crittall is just too expensive for me.

    I’d be grateful if you could point me in the right direction.

    Thank you.

  13. robert waters says

    Hello, we have a barn conversion project where there is a stipulation for to replace the existing steel windows with similar looking new, and the large openings we now have must have the same appearance. We have a 2.5 meter square barn door opening for which we want a door , that opens for a daily door and to allow the whole window to be opened on summers days. W w want minimal metal work but maximum thermal protection, as it being stone we lose heat. We have looked at a number of suppliers but can’t find anything that looks right. Can you help with a supplier. Hampshire area.

    • Nick Dardalis says

      Hello Robert, thank you for your comment on the Aluminium Trade Supply Website. I have replied on the thread and confirming by email.

      The Smart Systems Alitherm Heritage 47 system is excellent as a steel look door and window and is one of the most authentic looking products on the market presently. However it’s worth speaking with a local supplier and looking at the various design/profile options available with this and other systems.

      Aspire Bifolding Doors
      11 Castle Parade,
      Ewell By Pass,
      KT17 2PR
      020 8224 7431
      Please speak to John Small or James Wenlock.

      Jewel Windows (Bisley Showroom)
      279 Guildford Rd, Bisley, Woking , Surrey, GU24 9AG
      01483 369 389
      01252 757614
      10 Century Farm, Green Lane, Badshot Lea, Farnham, Surrey, GU9 9JH

      Hope this helps, please don’t hesitate to get in touch if you’ve any questions or need further information.

  14. Ash says


    Thank you for the excellent information on your website. We’ve recently bought a 1965 two-storey house in Cambridge. Possibly our biggest renovation cost will be replacing all the windows and doors. Most are the original steel with secondary double glazing (both in poor condition) with some pvc and wooden french doors added later. We would like to keep the slimline appearance, improve thermal efficiency and have the flexibility to add bifold or sliding doors. I’d thought aluminium was the way to go but your article has given me pause. Would replacing with crittal as ‘like for like’ mean less alteration to the window aperture and therefore less work and money or are the window sizes standard? What about thermal efficiency – I thought heat was lost through the metal frame? Would steel be significantly more expensive? it is not a heritage property but retaining the slim line look is essential I think. Is there anyone in our area you could recommend to help us with this somewhat daunting decision?

    Many thanks,

    • Nick Dardalis says

      Hello Ash, thank you for your comment on our website and your kind comments.

      It really depends upon the steel system you choose as it is no just Crittall that supply steel windows. The windows are all made to suit your aperture sizes and any associated making good required to internal plaster for example. All modern steel windows now incorporate a thermal break therefore you will get a thermally insulated window, whether aluminium or steel. The U Value/Window energy rating will also depend upon the glass specification used.

      Steel is a more expensive product but as good as aluminium steel replacement systems are, nothing beats the real thing. Windows like Crittall are excellent. Ultimately it is up to you but do get prices on both and have a look at both products to see what’s best for you.

      The Smart Systems Alitherm Heritage 47 system is excellent as a steel look door and window and is one of the most authentic looking products on the market presently.

      Local to you I can suggest.

      Harpenden Windows
      Unit 1 Southdown Industrial Estate,
      Southdown Road, Harpenden,
      Herts AL5 1PW
      01582 765988

      Hope this helps, please don’t hesitate to get in touch if you’ve any questions or need further information.