Energy saving windows: what to look for
Energy efficiency standards can be confusing. A good insulating window has a low U-value. Here is how to read the numbers, and what they mean for your home.
Uw tells the truth, Ug flatters
Most manufacturers quote Ug, the U-value of the glass alone. The Uw value refers to the whole window, including the frame (Uf) and the glass edge (psi), and is the true indication of the energy efficiency of a window or door. Always compare Uw.
According to the European standard DIN EN ISO 10077-1, Uw is calculated as (Af x Uf + Ag x Ug + lg x psi) divided by Aw. Internorm quotes a whole-window Uw as low as 0.62 W/m²K for the HF 310, a Passive House level.
Where the heat goes
Around 30% of a house's heat can be lost through its windows, which is why demand for high-insulation windows keeps rising. The glass is not the only factor. The frame and the connection to the wall matter as well, which is why Internorm frames are filled with energy-efficient laminates and not hollow chambers.
Argon and krypton between the panes conduct far less heat than air. Compared with double glazing, Internorm says triple glazing allows up to 40% more glazed area with no effect on heating costs.
SOLAR+ glazing: free heat from the sun
Internorm's SOLAR+ coating lets in about 20% more solar energy than standard triple glazing, which means more free heat on bright winter days, while keeping heat loss very low. It also supports up to about 10% more daylight.
Feel the difference the glass makes
Pick a type of glazing, then drag the outside temperature. The sliders show how warm the inside pane stays, how much heat leaves each square metre, and when condensation starts to form.
- A cold inner pane is what you feel as a draught
- Moisture condenses on the coldest surface in the room
- Triple glazing keeps that surface close to room temperature
- Inner pane
- 19.3°C
- Heat loss
- 17W per m²
- Whole-window U
- 0.8W/m²K
Indicative, from standard surface resistance (0.13 m²K/W) and typical whole-window U-values: single 5.0, older double 2.8, modern double 1.4, triple 0.8. Internorm quotes Uw as low as 0.62 on selected models.
What could better glazing save you?
A rough guide to the heat your windows lose in a normal Irish year, and how much of it triple glazing could save. Change the numbers to match your house and your latest bill.
An estimate, not a quote or a guarantee. It looks at heat lost through the glazing only, using typical whole-window U-values and about 2,100 heating degree days a year. Your survey will give exact figures.
- Heat lost through glazing now
- 0 kWh a year
- With triple glazing (Uw 0.8)
- 0 kWh a year
- Possible saving
- €0 a year
In their words
Real feedback from EWC customers, published on our reviews page.
“The fitting team were one of the most professional we have had onsite in the many years we have owned our house. Overall EWC offer a premium product in Internorm and their service matches the product.”Ian and Ann, Carlow2024 refurbishment
“The installation team did an amazing job and took time to ensure they were 100% happy and did not rush at any stage. The front door in particular has drawn comment from subsequent visitors.”Michael Russell, Dublin2024 new build
“The team take the time to listen to and understand the customer's needs with no hard sell. Our windows and doors fitted without any hassle and are super efficient and virtually soundproof.”Martin and Sile, Carlow2024 new build, DAKO triple-glazed uPVC
Energy saving: your questions answered
What is a good Uw value for windows?
Lower is better. Passive House level windows reach around 0.8 W/m²K or lower. Internorm quotes Uw as low as 0.62 W/m²K on its best models.
What is the difference between double and triple glazing?
Triple glazing has an extra pane and gas-filled gap, giving a lower U-value, a warmer inner surface, less condensation and better noise reduction.
Get your window and door quote
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