Tool

Energy Savings Calculator

By the WindowCost editorial team · SaaSquatch Ltd, London · Last updated 2026-04-21 · How we calculate

How much will you actually save on heating bills after replacing your old windows? This calculator uses U-value ratings, current UK energy prices, and your heating type to give you a realistic annual figure — not marketing fluff.

Estimated annual saving £— —

Heat lost through old windows: — kWh/yr
Heat lost through new windows: — kWh/yr
CO₂ reduction: — kg/yr
10-year total saved: —

Assumes UK heating degree-days (2,200 HDD baseline, adjusted by region), 2026 retail energy prices (gas ~6.5p/kWh, electric ~27p/kWh, heat-pump effective 8p/kWh at COP 3.5), and a heating season of roughly 200 days. Real savings vary with occupancy patterns, insulation in walls/loft, and boiler condition.

What affects real savings

Wall insulation first. If your walls are uninsulated solid brick, upgrading windows before walls captures only ~30% of the available savings. See our grants section for whole-fabric schemes.
Heat pump owners see the biggest proportional gain. Every kWh saved is expensive heat — a triple-glazing upgrade typically pays back 2–3 years sooner with a heat pump than with gas.
Triple glazing isn't always worth it. If you're on gas with a new boiler and well-insulated walls, high-spec double typically pays back faster than triple. See our double vs triple guide.

Next step

Payback Period Calculator — plug in your install cost and this annual saving to see your break-even year.
Grant Eligibility Checker — ECO4 / HUG2 / GBIS can cut your out-of-pocket install cost to £0 if you qualify.
Cost Calculator — get the install-cost side of the equation.

EPC glazing-uplift evidence base

Analysis of 23.1 million Energy Performance Certificates across England & Wales, showing how current glazing type relates to modelled energy improvement potential.

Glazing type prevalence across UK housing stock

Single glazing appears in just 0.06% of EPC records — likely an undercount since the least-efficient homes may be the least likely to have a current certificate on file. Secondary glazing (0.53%) and triple glazing (0.18%) remain rare.

Not recorded

9.0M 38.8%

Double glazing (vintage unknown)

6.2M 27.0%

Double glazing (post-2002)

4.6M 20.0%

Double glazing (pre-2002)

2.3M 10.0%

Other / unknown type

797.6K 3.4%

Secondary glazing

122.2K 0.5%

Triple glazing

42.3K 0.2%

Single glazing

12.8K 0.1%

Average EPC band uplift by current glazing type

How many EPC bands (A-G) the typical home moves from current to modelled potential rating. Higher means more headroom for improvement — not that the glazing type is thermally superior. Secondary glazing tops the list because it's fitted to period properties with other upgrade headroom. Triple glazing sits lowest because it's in already-efficient homes.

Secondary glazing

1.93 n=100.5K

Other / unknown type

1.93 n=687.9K

Double glazing (pre-2002)

1.77 n=1.9M

Double glazing (vintage unknown)

1.68 n=5.2M

Single glazing

1.68 n=10.2K

Not recorded

1.58 n=6.1M

Double glazing (post-2002)

1.50 n=3.5M

Triple glazing

1.44 n=27.2K

Current → Potential EPC band movement

75.8% of UK homes would improve at least one EPC band if all recommended measures were applied. The most common transitions are shown below.

D → B

4.8M 20.5%

C → B

4.2M 18.2%

D → C

3.3M 14.4%

C → C

3.3M 14.2%

B → B

1.7M 7.5%

E → C

1.4M 6.1%

B → A

1.2M 5.2%

E → B

1.1M 4.7%

D → D

371.7K 1.6%

E → D

296.2K 1.3%

EPC domestic dataset, aggregated 2026-04-24. Licensed under Open Government Licence v3 (OGL v3) — non-address fields only. Read the full analysis →