Czech energy auditing is governed by Act No. 406/2000 Coll. on Energy Management (Zákon o hospodaření energií) and its implementing Decree No. 141/2021 Coll., which replaced the earlier Decree No. 480/2012. The audit provides a structured assessment of a building's energy consumption and identifies technically and economically viable measures to reduce it. For residential buildings, the most relevant output is the energy performance certificate — průkaz energetické náročnosti budovy (PENB) — which is mandatory for buildings sold or leased and is a prerequisite for most subsidy programmes.
Legal Obligation vs. Voluntary Audit
A full energy audit (energetický audit) is legally required for buildings with annual energy consumption exceeding 1 500 GJ (approximately a district-heating block of 100+ apartments) and for large enterprises under the Energy Efficiency Act. For individual family houses and smaller apartment buildings, the audit is typically voluntary but required as a condition of grant applications under the New Green Savings programme (Nová zelená úsporám, NZÚ) and the Reconstruction programme of the Ministry of the Environment (OPŽP).
The PENB, by contrast, is mandatory for: sale or lease of any building or building unit; new construction; major renovation affecting more than 25% of the envelope area.
Who Can Carry Out an Audit
Only a person holding a valid authorisation from the Ministry of Industry and Trade (Ministerstvo průmyslu a obchodu, MPO) may issue a legally recognised energy audit or PENB. The register of authorised energy auditors (energetičtí auditori) and energy specialists (energetičtí specialisté) is publicly available at mpo-enex.cz/experti. The distinction matters: an energetický auditor issues the audit report, while an energetický specialista issues the PENB. One person may hold both authorisations.
What the Audit Covers
The audit assesses the building in its current state and proposes measures, ranked by cost-effectiveness. For a residential building the standard sections are:
- Building envelope: U-values of existing walls, roof, floors, windows and doors; identification of thermal bridges; air leakage assessment (blower door test result if available).
- Heating system: Boiler or heat pump efficiency, distribution losses, control and zoning.
- Hot water preparation: Energy demand, storage losses, solar thermal potential.
- Ventilation: Existing ventilation type (natural, mechanical exhaust, balanced with heat recovery); estimated infiltration heat loss.
- Lighting: For non-residential spaces within the building (common areas, stairwells).
Each measure is quantified in terms of: primary energy savings (kWh/year), CO₂ reduction (kg/year), investment cost (CZK), simple payback period (years) and the resulting energy performance classification improvement (A–G scale).
Energy Performance Classification (PENB Scale)
| Class | Description | Primary Energy Intensity |
|---|---|---|
| A | Extremely efficient | ≤ 0.50 × reference |
| B | Very efficient | 0.51–0.75 × reference |
| C | Efficient | 0.76–1.00 × reference |
| D | Less efficient | 1.01–1.50 × reference |
| E | Inefficient | 1.51–2.00 × reference |
| F | Very inefficient | 2.01–2.50 × reference |
| G | Extremely inefficient | > 2.50 × reference |
The reference value is calculated from the building's geometry and use according to Decree No. 141/2021 Coll. A standard uninsulated panel-block apartment building typically falls in class E or F. After full ETICS retrofit plus window replacement, class C or B is achievable. Adding heat pump heating and solar panels can reach class B or A.
Documents Required for the Audit
The energy auditor will typically request the following documents at the start of the assessment:
- Architectural drawings (floor plans, sections, elevations) — existing condition
- Utility bills for at least the past 3 years (gas, electricity, district heat)
- Boiler or heat pump technical data sheet
- Any existing PENB or previous energy study
- Window replacement records (if applicable)
- Land registry extract (výpis z katastru nemovitostí)
If drawings are unavailable, the auditor will conduct an on-site survey to measure the building geometry. For older buildings without any documentation, this survey can add CZK 2 000–5 000 to the total cost.
Blower Door Testing
A pressurisation test (blower door, EN ISO 9972) is not legally required for the standard PENB but is strongly recommended before specifying a heat recovery ventilation (HRV/MVHR) system. The test measures the air permeability at 50 Pa pressure difference (n50 in h⁻¹). Results below 3.0 h⁻¹ are required for the NZÚ programme's highest subsidy tier for family houses. Passive house standard requires n50 ≤ 0.6 h⁻¹.
Using the PENB in Grant Applications
The NZÚ programme requires a PENB both before and after the renovation for projects in categories C.3 (comprehensive renovation). The pre-renovation PENB establishes the baseline; the post-renovation PENB confirms that the required class improvement has been achieved. The improvement must be at least two energy classes (e.g. from E to C) to qualify for the highest subsidy rates.
For individual measures (insulation only, window replacement only), a PENB is not required but a project documentation prepared by an authorised person is. The NZÚ application portal at novazelenausporam.cz specifies the current required documents for each measure category.
Thermal Imaging as a Diagnostic Tool
Infrared thermography of the building exterior, carried out in winter when there is at least 10 °C difference between interior and exterior temperature, provides qualitative evidence of thermal bridges, missing insulation sections and air leakage paths. While not a substitute for the formal U-value calculation, thermographic images are routinely included in audit reports and can identify defects that are not visible in drawings.
Further reading: MPO — Energy Performance of Buildings | Wall Insulation Materials Guide →