How much do new windows really save on heating?
In short: Windows are one of the main places where a house loses heat. New PVC windows with low-emissivity glass lose several times less heat than old wooden ones. You save the most when the window, the glass and the installation are all done well.
Where a house loses heat
Heat leaves a house through the walls, roof, floor and windows. In an average family house, windows and doors account for roughly 15–25% of the loss. With old single-glazed windows or worn-out seals the share is higher, because cold air also gets in through the gaps.
So, to be honest: new windows alone will not halve your heating bill if the walls and roof are not insulated. But they are often the quickest step – a room takes a day or two, and you feel the difference straight away: no draughts and no cold wall next to the window.
What the Uw value means, simply
The Uw value tells you how much heat passes through 1 m² of the whole window (frame and glass together). The lower the number, the better the window.
Window | Uw (W/m²K), approx. |
|---|---|
Old wooden, single glass | about 5 |
Old wooden, two panes (coupled sash) | about 2.5–3 |
ARKA, Gealan S8000, double glazing | ≈ 1.3 |
ARKA, Gealan S8000, triple glazing | ≈ 0.9 |
Example: an old window with a Uw of about 3 loses roughly twice as much heat as ours with double glazing (1.3) and more than three times as much as ours with triple glazing (0.9).
The profile: Gealan S8000
Our windows are made from the German Gealan S8000 profile, 74 mm deep. White windows have a 5-chamber profile and coloured (decor) windows a 6-chamber profile. The chambers hold air and slow down the flow of heat, and the main chamber has a large steel reinforcement so that even large windows stay stable.
Gealan S8000 – manufacturer data | Value |
|---|---|
Profile depth | 74 mm |
Number of chambers | 5 (white) or 6 (coloured) |
Thermal transmittance of the profile (Uf) | down to 1.2 W/m²K |
Glass thickness | up to 48 mm |
Sound insulation (depending on glass) | 34–47 dB |
Watertightness (EN 12208) | up to class 9A |
Air permeability (EN 12207) | up to class 4 |
Wind resistance (EN 12210) | up to class C5/B5 |
Source: gealan.de – GEALAN S 8000. Uf is the value of the profile alone; the Uw of the whole window also depends on the glass.
Double or triple glazing?
Glass is the largest surface of a window, so it has the biggest effect on heat loss. Both of our glass units use low-emissivity glass. Low-e glass has a thin, invisible coating that reflects heat back into the room.
Double glazing is a good choice for most houses and flats.
Triple glazing pays off more on north-facing sides, for large glazed areas, in houses with well-insulated walls and where peace and quiet matter.
White single-sash window, 1000 × 1400 mm: RSD 27,220 with double and RSD 30,830 with triple glazing – including measurement, installation and VAT. See the price for your sizes in the calculator.
Installation is half the job
Even the best window loses heat if it is badly installed. The joint between the window and the wall has to be filled and sealed so that cold air and moisture cannot get around the window. That is why our own team does the measuring and installation, and the price includes both.
Finally
If you are thinking about replacing your windows, first get an estimated price in the calculator, then book a measurement visit. During the visit we will tell you which glazing makes sense for your house.