# Window Replacement Calculator — United Kingdom

> Combine a quoted per-window replacement price with a conductive heat-loss comparison using whole-window U-values. GBP planning view; stated limitations apply.

Page: https://askcalculators.com/uk/window-replacement/
Definition: https://askcalculators.com/uk/window-replacement/definition.json
JSON Schema: https://askcalculators.com/uk/window-replacement/schema.json
Version: 20.16.0
Maintained by: AskCalculators (software project; not a credentialed reviewer)
Qualified review: pending. Automated checks do not establish professional approval.
Page status: Live
Review status: Pending

## Use
Open the calculator page and enter values. Query-string parameters can restore and bookmark a calculation.
Example: https://askcalculators.com/uk/window-replacement/?unitSystem=metric&windows=10&windowArea=1.5&oldU=2.8&newU=1.3&degreeDays=2500&heatEfficiency=90&energyRate=0.1&unitRate=0&laborCost=0&deliveryCost=0&otherCost=0&costMultiplier=1&spreadPercent=15&taxRate=0

## Inputs
- unitSystem: Measurement system; type=select; optional; default=metric; values=imperial|metric
- windows: Number of windows; type=number; required; default=10; min=1; max=10000
- windowArea: Average area of one window; type=number; required; default=1.5; min=0.01; max=1000000000000
- oldU: Existing window U-value; type=number; required; default=2.8; min=0.01; max=20
- newU: Proposed window U-value; type=number; required; default=1.3; min=0.01; max=20
- degreeDays: Local heating degree days; type=number; required; default=2500; min=0; max=20000
- heatEfficiency: Seasonal heating efficiency; type=percent; required; default=90; min=0; max=100
- energyRate: Heating energy cost per input kWh; type=money; required; default=0.1; min=0; max=1000000000000
- unitRate: Material price per window; type=money; required; default=0; min=0; max=1000000000000
- laborCost: Total labor allowance; type=money; required; default=0; min=0; max=1000000000000
- deliveryCost: Delivery allowance; type=money; required; default=0; min=0; max=1000000000000
- otherCost: Other fixed costs; type=money; required; default=0; min=0; max=1000000000000
- costMultiplier: Material/labor multiplier; type=number; required; default=1; min=0.1; max=10
- spreadPercent: Low/high sensitivity around the entered total; type=percent; required; default=15; min=0; max=100
- taxRate: Explicit tax allowance; type=percent; required; default=0; min=0; max=100

## Outputs
- totalArea: Total window area; format=number
- annualInputSaving: Modeled heating input saved, kWh; format=number
- annualSaving: Modeled annual heating saving; format=currency
- materialCost: Material cost; format=currency
- laborCost: Labor allowance; format=currency
- deliveryCost: Delivery allowance; format=currency
- otherCost: Other specified costs; format=currency
- tax: Entered tax allowance; format=currency
- low: Low cost scenario; format=currency
- mid: Middle cost scenario; format=currency; primary
- high: High cost scenario; format=currency

## Formula
heating input saved = window area × (old U − new U) × degree days × 24 ÷ (1,000 × heating efficiency).

Inputs are converted to canonical units before evaluating this stated formula.

## Rules
- Empty optional inputs are undefined, not zero.
- Hidden conditional inputs are ignored.
- Do not invent missing required inputs.

Notice: Illustrative defaults are not local quotes or verified legal rules. Dated reference components and user-entered assumptions are explicitly distinguished. Professional review is pending.