# Furnace Replacement Calculator — United Kingdom

> Compare the fuel-cost consequence of two seasonal efficiencies at the same useful heating load. GBP planning view; stated limitations apply.

Page: https://askcalculators.com/uk/furnace-replacement/
Definition: https://askcalculators.com/uk/furnace-replacement/definition.json
JSON Schema: https://askcalculators.com/uk/furnace-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/furnace-replacement/?annualFuelCost=1800&oldEfficiency=75&newEfficiency=95&projectCost=7000&incentive=0&maintenanceChange=0&years=15&discountRate=4

## Inputs
- annualFuelCost: Current annual fuel-only cost; type=money; required; default=1800; min=0; max=1000000000000
- oldEfficiency: Current seasonal efficiency; type=percent; required; default=75; min=0; max=100
- newEfficiency: Replacement seasonal efficiency; type=percent; required; default=95; min=0; max=100
- projectCost: Installed replacement price; type=money; required; default=7000; min=0; max=1000000000000
- incentive: Confirmed incentive; type=money; required; default=0; min=0; max=1000000000000
- maintenanceChange: Additional annual maintenance; type=money; required; default=0; min=0; max=1000000000000
- years: Planning horizon, years; type=number; required; default=15; min=1; max=40
- discountRate: Discount rate; type=percent; required; default=4; min=0; max=50

## Outputs
- capital: Net capital cost; format=currency
- annualSaving: First-year net saving; format=currency
- payback: Simple payback, years; format=number; primary
- npv: Discounted net value; format=currency

## Formula
gross fuel saving = current fuel spending × (1 − old efficiency ÷ new 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.