Insulation payback calculator
Estimate annual heating energy and cost saved by changing an element’s U-value, using your local degree days, heating efficiency and installation cost.
Element area above 0 to 1,000,000 m², U-values 0 to 20 W/m² K, heating degree days 0 to 20,000 K days, heating efficiency or COP above 0 to 20, price per input kWh 0 to 100,000 and installed cost 0 to 1 trillion in one currency. Area accepts m² or ft². Calculated on your device. Downloads: JSON report and results CSV. This calculator uses the fields below. Results update as you type. Up to 1,000,000 characters.
Your result
How to use Insulation payback calculator
- Enter the insulated area and its whole-element U-values before and after the work.
- Enter local heating degree days in K days, heating efficiency or COP, and the price per input kWh.
- Enter installed cost and review annual energy and cost savings.
- Check the model boundaries before using simple payback, then download the JSON report or CSV.
Useful next steps
Annual heat transfer
The estimate uses U-value × area × heating degree days × 24 / 1000 to calculate useful heat in kWh. Use U-values for the whole element, including the construction layers you intend to compare. Enter local degree days at an appropriate balance temperature; Fahrenheit degree days must first be divided by 1.8.
From heat to cost
Useful heat is divided by heating efficiency or seasonal COP before applying the input-energy price. Enter 0.8 for 80% efficiency or 3 for a seasonal COP of 3. The example 100 m², U-values 1.5 and 0.5, and 2,000 K days saves 4,800 useful heat kWh.
Simple payback limits
Simple payback is installed cost divided by positive annual cost saving. Equal or worse U-values and zero tariffs can produce no payback or a negative saving. The model excludes cooling, thermal bridges, air leakage, solar gains, behavioural changes, grants, finance and tariff changes.