How to Tell a Good uPVC Window From a Bad One

Updated on April 11, 2019
Martin-ddp profile image

I've been writing on DenGarden for over 5 years and have over 25 years of experience working in the window and door trade.

Sample pvc window cert
Sample pvc window cert

What Makes a Good uPVC Window?

In today's market, you would think it would be easy to spot the differences between a good uPVC window and a bad one. For example, in the UK and Ireland, windows now come with a cert. This is an energy rating to tell you how good the window is at keeping the heat in. The rating starts at A being the best and B being next in line, and so on.

Problem sorted! Just look at the cert and you must be getting the best window. WRONG!

What if you go to a company that has been around for a good while and has an A-rated cert on their window. You are still not guaranteed.

So how do you tell then? With a little knowledge, that's how.

How a Window Gets an A Rating:

All that is needed is to change the reinforcement from steel or aluminum to a warmer reinforcement like carbon. This will reduce heat loss through the frame of the window. Then you must upgrade the double glazing so it also has a warm edge spacer bar and Low-E glass plus it must also be gas filled. Argon is the most common gas which is used. But with some window systems, this still is not good enough, and they must upgrade the gas to Krypton gas.

So now you know how the window gets an A-rated cert and is good at keeping the heat in. (What more do you need to know?)

Below is a list of a few other things you might find useful to know about uPVC windows.

uPVC Section: This is the plastic that is used to make your windows. Make sure there is at least a ten-year or more guarantee with the system. This should cover it from discolouring and warping.

Glass: Check what guarantee is with your double glazing. A lot of the older double glazing came with a seven-year warranty. But Most of the newer double glazing will come with a fifteen year or more warranty.

Locking System: There are many types of locking systems out there. Some window companies will just use the cheapest one on the market unless you ask for a better system. The most common one is the Espag locking system. But if you want a bit more security, then a shoot-bolt system is a better option.

Bead System: Is the bead system external or internal? (Internal means the glass can only be taken out from the inside.)

Fully Welded or Mechanical Joints: All uPVC windows would have the four corners of the frame and sash welded. But the mullions and transoms can be welded or mechanical. Mechanical mostly comes with older systems, but it is still around today. It is a quicker way to make windows; the main fault with this system is in some cases if the transoms or mullions shrinks even by half a millimetre, it can let a draught in.

Window Handles: There are loads of different types of handles being used. Some will only last six months to a year depending on how much use it gets. Other are designed to last five years or more. How do you tell one from another? That is the problem—it is very hard. The best thing to do is to make sure you have a two-year guarantee with all moving parts on the window. Plus, find out what their policy is on coming out to do repairs.

Hinges: These are just like the handle there are so many different types you don't know if they are good or bad until they start to fall apart. Again make sure there is a two-year warranty on all moving parts. If possible check with some of their older customers to see how they got on.

Screws Holding on the Hinges: This may not seem like much, but you don't want to open your window in a year's time and see a load of rust there, or worst have your sash fall out because the screws holding the sash in have rusted away. A lot of window companies will use zinc-coated screws, and on the bottom of a side-hung sash, these will be changed to stainless steel screws. But it is better if you had all stainless screws and if you live near the sea it is a must that you have all stainless steel screws.

How do you tell if they are stainless steel screws? Get a magnet, and if it sticks to the screw then it is not stainless steel. Magnets will not stick to stainless steel.

Interlockers: These are two-angle uPVC blocks which help the sash close properly and keeps it tight against the seal. Plus they also give your window better security. All window systems have these; the only reason they might not be on a window is because the fabricator was too lazy or just forgot. It happens and you would be amazed at how many windows these are left off.

So if you are about to invest in new windows, don't be afraid to ask the window company about any of the things you read here. If it looks like you know a bit about windows, you will find that you will get a better job done as they know you will be checking everything.


  1. What energy rating is the window (A-B-C-D)?
  2. Warrantees. There are three different ones, so ask about all three. (Section, Double Glazing, Moving Parts.)
  3. Internal or External glazed? (Internal is better for security.)
  4. Screws holding on hinges? (Stainless steel are best.)
  5. Locking system? (Shoot-bolt is one of the best security options.)
  6. Inter-lockers? (Make sure they are fitted.)

If you have any questions or comments, please feel free to post them in the comment box below.

Click thumbnail to view full-size
Image showing an internal beaded systempvc window espage locking systempvc window externalbeaded systempvc interlockers on a sashMechanical joint on a pvc windowSample pvc window certpvc window shoot bolt locking systemZinc Screws starting to rust after only six monthsFully welded pvc window inage showig sash and mullion joint
Image showing an internal beaded system
Image showing an internal beaded system
pvc window espage locking system
pvc window espage locking system
pvc window externalbeaded system
pvc window externalbeaded system
pvc interlockers on a sash
pvc interlockers on a sash
Mechanical joint on a pvc window
Mechanical joint on a pvc window
Sample pvc window cert
Sample pvc window cert
pvc window shoot bolt locking system
pvc window shoot bolt locking system
Zinc Screws starting to rust after only six months
Zinc Screws starting to rust after only six months
Fully welded pvc window inage showig sash and mullion joint
Fully welded pvc window inage showig sash and mullion joint

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This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.

Questions & Answers

  • Is the thickness of glass important in uPVC windows?

    Most double glazing today is 24mm or 28mm thick. With a Low-E glass on the inside pane. A lot has gone up to 32mm thickness made with 4mm thick glass. The overall thickness of these units will not make any different's to your window. Once they all have the Low-E glass.

    If a double glazed unit goes over a certain size, the glass will go up to a 6mm glass, but the over all thickness will stay the same. They just reduce the spacer bar thickness.

    By having your unit made with 6mm glass instead of 4mm glass can make a difference. The 6mm is more secure plus it is better at keeping noise out. The insulating factor will go up by a small bit, but not by anything you will notice in your heating bill.

    BUT what makes the differences to the insulating is what type of gas they fill the unit with. So if your unit is filled with an argon gas than the thicker the unit, the better it is. As you will get more gas in. Which means more insulating.

    Note: Low-e glass is used as standard these days. But with some suppliers, you will have to pay extra for the argon gas. Plus there are a few different types of gas being used which perform better than the argon gas. But you will have to pay extra again for this.

    Below is a few different types of unit makeups to give you an idea.

    - 28mm thick unit made with 4mm glass inside pane is Low-E (used as a standard today)

    - 28mm thick unit made with 6mm glass inside pane is low-E (extra secure plus keeps out more noise)

    -28mm thick units filled with gas (extra insulating)

    -32mm triple glazed unit made with 4mm glass and gas-filled (good at keeping noise out plus very good insulating factor)

  • In respect of the frame section of a window, what does good PVC section look like and what does the middle of the road section look like?

    On the inside of the section, a good one should have three to four different chambers inside. One is to take the reinforcement, and the others are to stop the cold traveling through.

    A bad one will only have two chambers inside which will allow more cold get through.

    PLUS a good section will come with a warranty of at least fifteen years that it will hold its color and shape.

    A bad PVC section will only come with a seven-year or less.

  • You mention beading. Would external beading not allow burglars easy access? Hence internal beading being offered? Am I oversimplifying?

    Most new windows come with internal beading, and the windows with external beading come with a wedge system to push glass outwards to stop beads been taken out. Or they might have a security tape to hold glass in. But in some of the older and cheaper systems if the wrong gasket is used you can still get the beads out from the outside. Plus if a cheap security tape is used then it will just lose its grip in a few years time. But the internal Bead system has none of these problems. In fact, the only way to get the glass out is from the inside even in the cheapest system.

  • Hello. How thick should the PVC be on the exterior of the home?

    Most PVC profile systems are now 70mm front to back, and the walls would be around 3mm thick and made up of 5 chambers or more. It's the different chambers that keep the heat in on a PVC window

  • Should the lock-side coupling of a UPVC door frame with sidelights on both sides be reinforced with plastic or steel?

    PVC-covered steel is typically used to reinforce UPVC door frames. Otherwise, your door will be quite wobbly when closing. But if you are going for a very high U-value, you should use a carbon reinforcement. I have never seen plastic used as it's just not rigid enough to stop the door from wobbling when closing.

© 2012 Martin


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    • profile image

      uPVC Windows and Doors 

      12 months ago

      Thank you for your post. This is excellent information. It is informative post for uPVC windows and doors

    • profile image

      uPVC Windows in India 

      17 months ago

      Very interesting Blog, which you have shared here about the UPVC windows. I am very thankful to you for posting this type of article here. uPVC Windows in India.

    • profile image

      Nidhi Agarwal 

      2 years ago

      Thanks for sharing nice article.

    • Martin-ddp profile imageAUTHOR


      2 years ago from Ireland

      NO steel is not better as it can draw cold through the frame - No window will get an A rating with steel reinforcement. Plus there is a carbon reinforcement that can be used now instead and some pvc profiles systems have been updated so they don't need reinforcement

      But in some cases depending on style and size of window you might need steel for a bit of extra strength.

    • profile image


      2 years ago

      Are steel reinforced windows better than full pvc windows

    • profile image

      monica teo 

      2 years ago

      Extremely useful tips. I shall bear that in mind. Can you comment on how good 'linair' upvc's window - believe they are British made. Wants to support British companies but have not heard of this new type of upvcs before. Should one be concern of this new product? Your views are great appreciated.


    • profile image


      3 years ago

      I have 45 years experience in the glazing, ali windows, PVC-u windows and sealed units. retired 10 years ago having been sales manager for some very good companies.

      I agree with some of the comments above but the question of guarantees is a very hot potato !! The companmy i last worked for guarantee the components and frames for 10 years with no compensation paid for the installation of the products. Most sealed units these days are very good, compared with some of the rubbish used in the past. Swiggle strip was used for some years but really is not worth using as is very unstable. The method of manufacture can be critical and is either done by hand using pumped sealant or fully automatic on very advanced lines.

      There was a period in the pvc window industry of north side yellowing when defective compound came over from europe but that is over now many years ago. Discolouration can occurr up to about 4%, however remember there are many shades of "white" in our industry!!!

      On the question of screws rusting, yes they may well do so unless austinetic screws are used but they are very expensive. Similarly hinges can be of this material but you wont want to pay for them. A wiipe with an oily rag helps but dont get oil on the slides or the window will not stay still bein the wind. There is a small screw which can tighten up the sliding action. The reason these screws rust is a voltage between dis-similar metals with water on them which, believe it or not, will produce a small electrical charge. As another contribtor has posted, stainlees comes in many forms. The word is stainLESS not neccessarily stainFREE !!!

      Most windows are welded these days on sophisticated multi-head welders with weld sprews being removed by a shallow grooveing machine both on transoms and corners. This does not effect the strength of the welds. Galvanised steel reinforcing is used predominately now due to the cost of aluminium.

      The pvcu windows are sold as "maintanance free" which is incorrect. Keep moving mechanisms clean, a quick squirt of dw40 will keep door locking mechanisms free. Molibdinum or a carbon powder puffer into the key slot will keep the key turning freely.

      On the subject of glazing beads, most are now or should be internally applied for security. Insist they are.

      If you live high up use self cleaning glass, it works well.

      my big bugbear is the introduction of trickle vents in the outerframes of the windows to building and fensa regs. This has changed from a requirement to a reccommendation from october 1st 2014. Look on building regs for further help on this subject. I hate them because we made very good A rated windows but the trickle vents are draughty in a storm.

      Hope this helps. We are a good industry now that most of the dagos that used to be in it have died or moved on !!

    • Martin-ddp profile imageAUTHOR


      6 years ago from Ireland

      Some systems have a square bead. But if all the others that you are looking at are angled and if some of them got the windows in the same place as you than more than likely yours should be angled to. In a lot of external beaded systems the top and bottom bead will be a straight cut. Than the two heights will be an angle cut. For the very reason that you said. So the rain will run off them.

    • profile image

      John Nichols 

      6 years ago

      The bead on the outside of the window should it be angled or square mine is square and the corners are not mitred I thought it had to be angled so rain runs off. Every window I have looked at In my rd the breeding is angled

    • Martin-ddp profile imageAUTHOR


      6 years ago from Ireland

      Stainless steel is not a single kind of steel. It is a generic name for a wide range of corrosion-resistant steels. The properties of these steels vary and some of them are magnetic. Due to the fact that there is magnetic and non-magnetic stainless steel. The 400 series is the magnetic stainless steel while the 300 is the non-magnetic stainless steel.

      You will find that the 300 series is the one used with pvc windows. That way if a window is fitted next to the sea the salt air will not affect it

    • profile image


      6 years ago

      You mentioned how to tell if a screw was stainless steel by using a magnet.

      You said that if it was stainless steel a magnet would not stick to it, but you are wrong. A magnet will stick to stainless steel, but not to aluminum.


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