What you need to know about windows before you buy?
Purchase windows This is not shopping on Allegro, where at most you order the wrong colour of sweatshirt and send it back. Here we are talking about a decision that will stay with you for the next 20-30 years. A window is not only glass in a hole. This warmth, silence, safety and aesthetics, and if something goes wrong - that's also stress, fungus on the wall and a draught in the living room. So before you click "order", read this guide to the end, and then you can confidently call us - at GM PLAST we know what it's all about 😎.
1. Not every window it's window. The type of profile matters
When choosing windows, most people are guided by whether 'pretty' and 'whether the colour matches the roof'. And the truth is what is most important sits inside. We are talking about the profile, i.e. the plastic 'skeleton' of the window. It is responsible for:
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thermal insulation (will it be warm),
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sound (can you hear your neighbour mowing at 7am),
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static (whether it will not bend after 5 years),
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appearance (whether it will be thick, slim, streamlined...).
The most popular systems today are:
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Kömmerling 76 AD/MD - tops when it comes to quality and durability.
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Decco - more economical, but still robust.
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Salamander, Aluplast, Veka - also very good, depending on the version.
AD stands for rebate seal (two gaskets), and MD - centre seal (three gaskets). MD gives better insulation, more airtightness and is recommended for energy-efficient homes.
If someone is pushing AD to you as 'passive', then something stinks here
2. Glazing packages - 2 or 3? Or maybe 6?
It's well known - it's not the number of panes that counts, it's how they were made 😅
But seriously - today the standard is 3-glazed packages, i.e. 2 chambers, 3 panes of glass, noble gas (usually argon), warm spacer and low-e coatings.
What is the difference between the panes?
| Parameter |
What does this mean? |
| Ug |
Thermal transmittance (the lower, the better - e.g. 0.5 W/m²K is a luxury) |
| G-Value |
The amount of light/sun that enters |
| Sound absorption |
Will the neighbours continue to annoy you |
If someone offers you 4/16/4 panes, it's a relic. Aim for 4/18/4/18/4preferably with a frame Swisspacer Ultimate - is a kind of Rolls-Royce among frames.
3. Fittings - details that keep the window in place
It is the fittings that are responsible for:
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easy opening and closing,
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micro-ventilation (i.e. a slightly ajar window in winter without draught),
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security (RC2 class? Please do),
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comfort (tilt with lock, brake, anti-traction functions).
Top brands include:
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ROTO NX - our favourite, quiet, smooth and reliable,
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Winkhaus - also great, very safe,
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GU, Siegenia - solid players.
If the manufacturer doesn't say what it's fitting, more often than not... there's nothing to brag about 😅
4. Warm installation - without it you lose everything good they give windows
This is the most common mistake investors make: they buy the grazing windowsand then the 'foam and bye-bye' installation.
As a result:
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thermal bridges (i.e. heat escapes sideways),
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Dampness and fungus in the corners,
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draughts and a decrease in insulation by several tens of percent.
Warm installation is the assembly:
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with vapour-proof and vapour-permeable strips,
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often in the insulation layer,
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with appropriate wedges and washers.
Yes, it costs a bit more. But on a whole-house scale, these are pennies that make a HUGE difference.
Don't skimp on the installation. Seriously.
5. Ventilation - or how not to hunker down in winter
Modern buildings are so airtight that they are... all too airtight. Without ventilation, it becomes stuffy, steamy and... fungal 🍄.
Consider:
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ventilators - hygroregulated, pressurised, manually controlled - allows fresh air in even when the window is closed,
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microventilation - the classic "minimum tilt",
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windows with unsealing function - ideal for winter.
And in the summer? Don't forget to mosquito nets - Mosquitoes are like AI: the newer the version, the more annoying 🤬
6. Window terraces, balconies, sliding - what to choose?
The options you have are:
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Window Tilt-and-turn balcony doors - classic, cheap and simple.
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PSK - sliding-tilt - Slightly more expensive, but great for large glazing.
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HS - Lift-and-slide - luxury, mega-convenience, but also a specific price.
If you have the budget and want the 'WOW' effect - take HS.
If you just want to go out on the balcony without bumping into the handle - take the classic ones, but with good hinges.
7. Accessories - and yet they make a difference
Often overlooked, and then there is crying:
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Muntin bars - decorative stenciling between the panes - adds to the retro charm.
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Balcony latch - you go out and close the door from the outside.
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Brake in the handle - so that the wind doesn't beat the wing against the wall.
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Opening restrictors - useful with young children.
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Handle misalignment locks - so as not to break the mechanism.
8. How much does it cost? That is, the most common question of all time
Well, here we go with an indicative price list (as at the date of writing - end 2025):
| Product |
Gross price (indicative) |
| White 2-pane window 116×143 |
From £650 |
| White 3-pane window 116×143 |
From £850 |
| Single-sided colour |
+20-30% |
| Two-sided colour |
+40-50% |
| Coloured core |
+150-250 zł |
| Warm installation |
+£100-150/unit. |
| Mosquito nets |
From £120 |
| Ventilators |
From £90 |
But remember - a window for £200 cheaper can have:
Sometimes it is better to add 100-200 zloty and sleep soundly.
9. What to watch out for? The 5 most common customer mistakes
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Buying only on price (and then crying that it steams and makes noise).
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No questions asked about installation (or a cheap team from 'John from Construction').
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Ordering windows without measuring (true story - windows bigger than openings...).
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No ventilation - and then children with runny noses and fungus in the corner.
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A mismatch of colours and cores - and then the window looks like Frankenstein.
✋ Summary - what is worth remembering?
✔ Windows is an investment, not an expense.
✔ Look not only at the appearance, but at the profile, glazing and installation.
✔ Don't skimp on key components - especially sealing.
✔ Compare offers - not just prices, but what's in it.
✔ And most importantly - ask questions. A good manufacturer/trader will explain everything to you.
And if you don't have the time or inclination to delve in - give us a call.
W GM PLAST We have been in business since 1998, we have completed thousands of projects, and we treat every window as if it were to be installed in your own home. No compromise, no bullshit.