Energy estimate
What would they save?
An estimate, worked out in the open: the heat that leaks through your windows now, less what leaks through A-rated ones, over a South Wales heating season, turned into gas, pounds and carbon. Every assumption is written underneath.
Your windows now
1 windows · Single glazing to A-rated
£20 a year
About 340 kWh less gas and 60 kg less CO2 a year, at today's gas price. Over twenty years at that price, about £400.
Real savings depend on how warm you keep the house, how draughty the old windows are, curtains and blinds, and the gas price. Draught-proofing is not counted, so a draughty house will usually save more.
- Glass and frame: 1 × 1.4 m² = 1.4 m²
- U-value now 4.8, new 1.2: 3.6 W/m²K less
- 3.6 × 1.4 = 5 W for each degree inside over outside
- × 57,600 degree-hours a year ÷ 1,000 = 290 kWh of heat
- ÷ 0.85 boiler efficiency = 340 kWh of gas
- × 6.5p = £20; × 0.183 kg = 60 kg CO2
At a glance
A year’s saving by house size.
The same assumptions, rounded to £5. Your row is marked.
| Windows | From single glazing | From old double glazing |
|---|---|---|
| 4 windows | £90 a year, 250 kg CO2 | £40 a year |
| 6 windows | £135 a year, 380 kg CO2 | £60 a year |
| 8 windows | £180 a year, 500 kg CO2 | £80 a year |
| 10 windows | £220 a year, 630 kg CO2 | £100 a year |
| 12 windows | £265 a year, 750 kg CO2 | £120 a year |
| 14 windows | £310 a year, 880 kg CO2 | £140 a year |
The assumptions
- An average window, glass and frame1.4 m²
- Single glazing in a timber or metal frameU 4.8 W/m²K
- Double glazing from before 2002, air-filledU 2.8 W/m²K
- Our A-rated window, whole-windowU 1.2 W/m²K
- Heating season in South Wales, about 2,400 degree-days57,600 degree-hours
- Gas boiler efficiency85%
- Gas price, about6.5p a kWh
- Carbon from burning gas0.183 kg CO2 a kWh
Start with a free survey.
Kerry measures every opening with a laser, checks the lintels and the cills, shows you the colours and the glass, and writes a fixed quote at your kitchen table. The quote builder gives you the band before she comes.