June 3, 2026, 9:31 am | Read time: 2 minutes
Insulation can significantly reduce heating costs and increase living comfort. However, caution is advised when providers make blanket statements like “insulation saves 50 percent of energy.” The actual savings always depend on the specific building.
The Schleswig-Holstein Consumer Center also warns against blanket advertising promises. “General percentage figures without comprehensible calculations or measurements are not technically reliable and can mislead consumers,” say the consumer advocates.
The Real Impact of Insulation
How much energy an insulation measure saves cannot be answered with a single percentage. Key factors include:
- the construction and current condition of the house
- the existing heating system
- the individual heating behavior of the residents
Even the question of what temperature to heat to significantly affects energy consumption.
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Using Calculations for a Realistic Assessment
Those who want to know if facade insulation is financially worthwhile should calculate the potential savings as concretely as possible. The Schleswig-Holstein Consumer Center provides a calculation method on its website.
Three values are multiplied together for this:
- the difference between the thermal transmittance (U-value) of the facade before and after insulation
- the heating effort during the heating period (in kilokelvin hours, kKh)
- the facade area to be insulated
The result shows how many kilowatt-hours (kWh) of heating energy can be saved per year. If you also know the current energy price, you can calculate the annual savings in euros. This allows you to estimate how many years it will take for the investment to pay off—or whether it is economically worthwhile at all.
Where to Get the Necessary Data
Homeowners can sometimes find information about the current condition of the facade in construction documents or old plans. Alternatively, wall thickness and building material can be determined. With the help of appropriate online calculators, the U-value of the exterior wall can often be determined from this.
For heating effort, consumer advocates recommend the so-called degree-day number. This can be found in the technical paperwork. If it is given in Kelvin days, it can be converted for the calculation: The value is first multiplied by 24 and then divided by 1,000.
The facade area does not need to be measured to the centimeter. According to the consumer center, in many cases, it is sufficient to use the area that a professional company has already included in its offer.
With material from dpa