HesapHanem

Loft Insulation Savings Calculator

Enter your loft area, current and new U-values and energy price to see what better insulation saves you.

How it is calculated

Enter the loft area in m², the current and new U-values in W/m²K, your location's heating degree days per year, the energy price per kWh and the heating system efficiency in percent. Heat saved through the ceiling is (U old − U new) × area × degree days × 24 / 1000 in kWh per year. Dividing by the efficiency (for example 0.90) gives the extra fuel or electricity you would otherwise have to buy: kWh saved = heat saved / efficiency. Savings are kWh saved × price, and the 10-year figure is simply ten times the annual saving, with no price rises or discounting. The new U-value must be lower than the old one, otherwise there is no result. Degree days depend on your climate and the base temperature used, so take them from a local source.

Worked example

A 50 m² loft goes from U 2.3 to U 0.16, in a climate with 2,200 heating degree days, with energy at 0.12 per kWh and a 90 % efficient system. The U-value drop is 2.3 − 0.16 = 2.14. Heat saved = 2.14 × 50 × 2,200 × 24 / 1000 = 5,650 kWh. Divided by 0.90, the energy you no longer buy is 6,277 kWh a year. At 0.12 per kWh that is $753.28 a year, or $7,532.80 over ten years.

Try this example →

Common mistakes

  • Entering insulation thickness or an R-value in the U-value fields: U is the reciprocal of R, and mixing them gives nonsense.
  • Entering the new U-value higher than the old one, or equal to it, which returns no result because nothing is saved.
  • Using a degree-day figure with a different base temperature than the one your region normally quotes, or a single cold winter's figure instead of a typical year.
  • Entering the efficiency as 0.9 instead of 90: it is read as 0.9 %, which multiplies the energy saved by 100.
  • Treating the 10-year figure as a forecast: it assumes constant prices and weather, and it ignores the cost of installing the insulation.

About this calculator

A material's U-value measures how much heat passes through it — expressed in watts per square meter per degree Kelvin (W/m²K) — so a lower U-value means better insulation. Upgrading loft insulation lowers the roof's U-value, and the annual heating energy saved is calculated as the loft area multiplied by the difference between the old and new U-values, multiplied by the year’s heating degree days and 24 hours, divided by your heating system’s efficiency to give the energy you buy, and then converted into cost using the energy price per kWh.

Homeowners run this calculation before spending money on loft insulation upgrades because the return on investment varies enormously depending on the starting U-value — going from poor, aging insulation (a high U-value) to modern standards saves dramatically more energy per pound spent than topping up insulation that already meets current building-code minimums, where the diminishing returns mean payback periods stretch out much longer.

Was this helpful?

You can pick up to 3 reactions.

Comments

  • Be the first to comment.

Popular calculators

Loan Calculator

Monthly payment, total interest and full amortization schedule.

Percentage Calculator

Percent change, percent of, and ratio calculations.

Discount Calculator

Calculate final price, savings, and discount amount.

BMI Calculator

Body mass index from height and weight (metric or imperial).

Age Calculator

Compute your exact age in years, months and days from a birth date.

Compound Interest Calculator

Calculate the final amount and interest earned with compounding.

All Calculators