Draught-proofing savings calculator
Supply all building, heating and price assumptions. Add optional after-rate scenarios to compare with the same starting rate.
A QUICK WALKTHROUGH
How to use this tool
- Enter volume, both air-change rates, seasonal temperature difference, heating hours and efficiency.
- Enter the heat coefficient, fuel price, installation cost and currency; optionally add up to 20 after-rate scenarios.
- Calculate and review the signed changes and payback; copy or download the full report.
Assumptions and limits
Use a coefficient appropriate to your chosen model and a heating-season average temperature difference. Rates, temperature, efficiency and prices are held constant. Fabric heat loss, weather variation, moisture, indoor air quality, finance and price changes are outside this calculation. No coefficient or ventilation rate is preset.
Calculate
Loss = k × ACH × V × ΔT. Heat change = (loss before − loss after) × H / 1000. Fuel change = heat change / (η / 100). Cost saving = fuel change × price. Payback = installation cost / positive cost saving.
Main result
Positive changes mean savings; negative changes mean extra demand or cost. This model does not select a ventilation rate. Natural air-change rates are different from blower-door n50 readings. JavaScript floating-point estimates. The report shows raw numeric inputs → parsed JavaScript values and computed JavaScript numbers without rounding for display.
GOOD TO KNOW
Common questions
What happens if the after-rate is higher?
Signed changes are negative and the tool reports no positive payback.