Home insulation calculator: how much will you save in Poland
Choose a wall or ceiling, the insulation material and its thickness. The calculator works out the U-value before and after the work, how much heat and money you save a year with your heating, and when the cost pays back.
Example: 180 m², solid brick, 38 cm, 15 cm
Saving of about 5,596 PLN a year, heating with: natural gas
heating with: natural gas
U from 1.51 to 0.23about 17,149 kWh less heat per seasonpays back in about 9.0 years
- Before1.51 W/(m²·K)
- After0.23 W/(m²·K)
U 0.23 exceeds 0.20 W/(m²·K). 18 cm of white polystyrene (EPS) is enough.
| Item | Value |
|---|---|
| U before insulation | 1.51 W/(m²·K) |
| U after insulation | 0.227 W/(m²·K) |
| Heat loss through the element before | 20,184 kWh/yr |
| Heat loss through the element after | 3,034 kWh/yr |
| Heat saved | 17,149 kWh/yr |
| Energy or fuel you buy less | 18,052 kWh |
| Yearly saving | 5,596 PLN/yr |
| Insulation cost | 50,400 PLN |
| Grant or tax relief | 0 PLN |
| Cost after grant or relief | 50,400 PLN |
| Simple payback | about 9.0 years |
| Minimum thickness under WT 2021 | 18 cm |
| Boards or rolls, no offcut allowance | 180 m² |
| Insulation volume | 27.0 m³ |
Assumptions and formula11 October 2026
Thermal resistance before insulation
R = 0.13 + 0.38 ÷ 0.77 + 0.04 = 0.664 m²·K/W; U = 1.51
Resistance and U after insulation
R = 0.664 + 0.15 ÷ 0.040 = 4.414 m²·K/W; U = 0.227
Heat saved per season
Q = 1.281 × 180 m² × 3,100 × 24 ÷ 1000 = 17,149 kWh/yr
Saving and payback
saving = Q ÷ efficiency × energy price
17,149 ÷ 0.95 × 0.31 = 5,596 PLN/yr
payback = (cost - grant) ÷ saving
(50,400 - 0) ÷ 5,596 = 9.0
Layer resistances are calculated to three digits and U is shown with two decimal places. The WT 2021 limit is compared with the unrounded value.
- Rsi, internal surface resistance
- 0.13 m²·K/WPN-EN ISO 6946:2008, surface resistance table (ProAkademia summary)
- Rse, external surface resistance
- 0.04 m²·K/WPN-EN ISO 6946:2008, surface resistance table (ProAkademia summary)
- U(max) under WT 2021
- 0.20 W/(m²·K)WT 2021, annex 2 (Journal of Laws 2022 item 1225); may be applied until March 2028 (art. 102a of the Construction Law)
- λ of the element: Solid brick, 38 cm
- 0.770ITB Building Physics Department data and PN-EN 12524:2003 (ProAkademia summary)
- λ of insulation: EPS
- 0.040 W/(m·K)Holcim Biały FASADA PRO 040, declaration of performance BFP 040-01/26 of 8 June 2026
- Degree days (base 18°C)
- 3,100Eurostat nrg_chdd_a, Poland, 2016-2025 average (about 3119)
- Efficiency: natural gas
- 0.95
- Price: natural gas
- 0.31 PLN/kWhmyORLEN (formerly PGNiG OD) W-3.6 tariff, Oct 2026, with PSG distribution
- Insulation cost per m²
- 280 PLN/m²KB.pl, wall insulation prices 2026: 15 cm polystyrene with materials
An estimate for one building element, without thermal bridges, windows and ventilation. The real saving depends on how you heat the house.
How electricity, gas, pellet and coal prices have changed, month by month. Price history
Ready-made calculations
How to use the calculator
- Choose what you insulate: walls, or a ceiling or roof. Enter the area in m².
- Choose what the element is made of now. If you know its U-value, e.g. from an energy audit, choose I know the U-value and enter it.
- Choose the insulation material and set the thickness with the slider or type it in cm.
- Choose your heat source and check the energy price. Enter the insulation cost per m² from a quote and any grant or tax relief as a percentage.
- Click Calculate savings. The result updates with every change, and the formula with your numbers is in the assumptions.
What insulating a brick wall gives: an example
The calculator starts with 180 m² of uninsulated solid brick wall, 38 cm thick. Such a wall has a U-value of about 1.51 W/(m²·K). With 15 cm of white EPS (λ 0.040) the U-value drops to about 0.23, and about 17,149 kWh less heat escapes through the wall each season.
With a gas boiler that is about 5,596 PLN a year, with a heat pump about 5,096 PLN, with pellets about 9,594 PLN. At an average 280 PLN/m² the work costs 50,400 PLN and pays back in about 9.0 years with gas and about 5.3 years with pellets. The thermal modernisation tax relief at the 12% rate cuts the cost by 6,048 PLN and the gas payback to about 7.9 years.
How we calculate
The resistance of each layer is its thickness in metres divided by its λ value: R = d ÷ λ. The U-value is the inverse of the sum of resistances plus the surface resistances from PN-EN ISO 6946: U = 1 ÷ (Rsi + R1 + R2 + Rse). For a wall Rsi is 0.13, for a ceiling or roof 0.10, and outside Rse = 0.04 m²·K/W.
Heat saved per season comes from degree days: Q = (U before - U after) × A × HDD × 24 ÷ 1000. We use 3,100 degree days, the Eurostat average for Poland in 2016-2025. Kilowatt hours become zloty the same way as in the heating cost calculator: divided by the efficiency of the heat source and multiplied by the energy price. Payback is the insulation cost minus any grant, divided by the yearly saving.
Which thickness meets WT 2021
The Polish building regulations WT 2021 required external walls to have a U-value of at most 0.20 W/(m²·K), and roofs and ceilings below an unheated attic 0.15. The regulation expired in September 2026, but art. 102a of the Construction Law allows these requirements to be applied until March 2028.
15 cm of white EPS on a 38 cm brick wall gives a U-value of about 0.23, so it misses the limit. 18 cm of EPS λ 0.040, 16 cm of mineral wool λ 0.036 or 14 cm of graphite EPS λ 0.031 is enough. The calculator shows the minimum thickness of the selected material for any element.
What the calculator leaves out
We calculate heat transfer through a single element. Thermal bridges (ring beams, lintels, balcony slabs), windows and ventilation are left out. A ceiling below an unheated attic loses less in practice than the formula shows, because the attic air is warmer than outside.
In old houses real consumption is often lower than calculated, because some rooms are not heated to 20°C. The saving in zloty will then be lower too. The payback ignores changes in energy prices and the time value of money. The thermal modernisation relief has a limit of 53,000 PLN per taxpayer, which the calculator does not check.
Frequently asked questions
Is it worth insulating a house in Poland?
It pays most to insulate a wall or ceiling that has no insulation at all. In the calculator example, 180 m² of 38 cm brick wall insulated with 15 cm of EPS pays back in about 9.0 years with gas. If the wall already has 5 cm of old polystyrene, the same work saves about 1,671 PLN a year and the payback grows to about 30.2 years. Then it mainly makes sense together with a facade renovation.
How many cm of polystyrene does a wall need?
For a 38 cm solid brick wall, the WT 2021 requirement (U up to 0.20 W/(m²·K)) is met by 18 cm of white EPS λ 0.040 or 14 cm of graphite EPS λ 0.031. For a 24 cm aerated concrete wall 17 cm of white EPS is enough.
How do I calculate the U-value of a wall?
Add up the layer resistances (thickness in metres divided by λ) and add the surface resistances 0.13 and 0.04. For 38 cm solid brick: R = 0.13 + 0.38 ÷ 0.77 + 0.04 = about 0.664 m²·K/W, so U = 1 ÷ 0.664 = about 1.51 W/(m²·K).
Is insulating the ceiling worth it?
In the calculator example it pays back faster than the walls, because a square metre costs less. 100 m² of concrete slab with 5 cm of old wool, topped with 20 cm of wool λ 0.036, goes from a U-value of about 0.76 to about 0.15. That is about 4,569 kWh less heat, or about 1,491 PLN a year with gas. At 109 PLN/m² net, i.e. 10,900 PLN, the payback is about 7.3 years.
How much does insulating a house cost in 2026?
According to KB.pl price surveys from 2026, insulating walls with 15 cm of polystyrene including materials costs about 280 PLN/m² on average, with mineral wool about 347 PLN/m², and insulating a ceiling without a frame about 109 PLN/m² net. Enter your contractor's quote in the calculator.