How We Calculate This
The reference case is the Energy Saving Trust's semi-detached single-to-A-rated double-glazing example.
WINDOWS REPAIR, UPGRADE & REPLACEMENT CALCULATOR
Should You Repair, Improve or Replace Your Windows?
Start with the problem you need to solve. Compare affordable repair and improvement options before considering complete window replacement.
✓ Repair First Where Suitable✓ Compare Practical Improvements✓ Understand Replacement Costs
What Would You Like to Do?
Begin with a repair or improvement where appropriate. Select replacement only if you are considering new windows. No savings are invented for repairs or glazing options without a matching evidence-based reference.
Switch routes at any time. Your entered quote stays with the selected route.
1. What Is Wrong With Your Window?
These are common starting points, not a remote diagnosis.
Suggested selection follows your symptom; an installer must confirm suitability.
Repair Suitability & Safety
Check the existing frame, ventilation and safety before undertaking work.
1. Improve Existing Windows
Costs and energy benefits vary widely by window type, area and suitability. Use a written quotation.
Improvement Guidance
Draught-proofing can improve comfort when windows are suitable. Essential ventilation must be retained.
1. Your Current Windows
For a home with some existing double glazing, do not use an entirely single-glazed estimate.
The official £85 saving example is specific to a gas-heated semi-detached home in Great Britain.
2. Your Proposed Windows
Only the single-to-A-rated double-glazing reference has a verified bill-saving starting point. Other options show costs without invented savings.
Frames influence cost, appearance, upkeep and thermal performance. We don't apply unsupported material multipliers.
2. Costs & Financial Assumptions
For repairs and improvements, enter an actual quote. There is no trustworthy universal price for every repair or window size. The calculator will not invent one.
Leave blank until you have a quote. Costs vary by fault, number of windows, access and location.
Assume £0 unless funding is independently confirmed.
Editable illustrative price; savings scale against the 7.97p reference assumption.
100% = published reference; other percentages are what-if cases, not property predictions.
✓ Results Update Automatically
Your Estimated Results
Your Selected Scenario
For a repair, enter a quote to see the upfront cost. Savings are not calculated without a reliable reference.
Estimated Work Cost—Ask for an itemised quotation
Potential Annual Heating-Bill Savings—Only where a matched published replacement reference is applicable
Net Upfront Cost—After confirmed funding, if any
Carbon Impact—Only for the supported replacement scenario; not a measured reduction
ILLUSTRATIVE ANNUAL BENEFIT—
SIMPLE PAYBACK PERIOD—
Payback excludes maintenance, finance, future price changes and non-energy benefits.
Illustrative Cumulative Savings Over 25 Years
Constant annual bill savings and upfront replacement cost. Not a full financial forecast.
Cumulative benefit Net upfront cost
What These Results Mean
Select your existing glazing and planned improvement.
Comfort & Noise Benefits
Modern, appropriately specified windows can reduce draughts, cold surfaces and external noise, but benefits depend on installation, the frames, glass and ventilation.
Before You Proceed
Check ventilation, fire escape, safety glazing, building regulations, installer certification and planning restrictions.
Suggested Next Steps
- Describe the Fault
- Ask a Repair Specialist
- Get an Itemised Quote
- Confirm Safety & Guarantees
Repair, Improve or Replace?
Repairable faults may include draughts, hinges, handles, locks, damaged timber and failed sealed glass units. Ask a competent repairer to confirm whether existing frames are sound before committing to complete replacement.
Secondary glazing, appropriate draught-proofing and correctly chosen upgrades may improve warmth and noise comfort without full replacement. Avoid blocking required ventilation. For historic windows, consult conservation guidance before altering original fabric.
For complete replacement, compare whole-window energy ratings, guarantees, fire-escape needs and installation quality. U-values alone do not capture all performance.
Official Guidance
Methodology, Sources & Limitations
Repair and improvement routes deliberately use only a homeowner-entered quote and produce no invented bill savings, CO₂ figure or payback. Energy Saving Trust estimates around £250 for professional draught-proofing of windows and doors across a whole house, and about £55/year savings from draught-proofing around windows, doors and floors in Great Britain. Those numbers describe different combined scopes and must not be assigned to a single-window repair or one glazing improvement. Historic England recommends repairing suitable traditional windows and considering reversible secondary glazing; damp, ventilation, access, safety and heritage restrictions must be assessed.
For the replacement route only, the source is Energy Saving Trust's updated 2026 energy-efficient windows guide. An entirely single-glazed, gas-heated semi-detached house in Great Britain upgraded to A-rated double glazing has an example installed cost around £4,800, annual energy-bill savings of £85, and a published approximate 290 kg annual CO₂ reduction. These are published reference values, not derived from a window-count or U-value model. This prototype does not calculate heat loss from dimensions, orientation, frame condition, whole-window rating, heating demand or climate. The £85 amount is scaled only by a labelled what-if percentage and editable tariff factor, not represented as a certified calculation.
When the baseline, improvement or house reference differs, savings, carbon and payback are deliberately withheld pending a property-specific survey. For a scenario based on the published reference, annual CO₂-equivalent context starts from its 290 kg/year example and scales with the same what-if factor. This is not an independently modelled or guaranteed carbon benefit. Comfort, noise and condensation improvements are qualitative and may differ.
A 25-year cumulative-benefit graph assumes unchanged yearly savings; it omits future energy tariffs, financing, maintenance, weather, inflation, glazing failure, time value of money and the fact that windows are often replaced for reasons other than energy savings. It is not an investment forecast. Check fire escape, ventilation, structural changes, conservation/listed-building rules and building-regulation certification with the installer and applicable local authority.