Improving your EPC rating in Belgium: why geothermal is a strong lever

In Belgium, whether in Brussels, Wallonia or Flanders, the energy performance certificate (EPC, or PEB/EPB) has become the most important document in a property transaction. A poor rating (F or G) can cut the price of a house by 20 % or 30 %. Conversely, an A or B rating guarantees immediate added value. At WellDoneDrill, we help our clients transform their certificate thanks to vertical drilling.

1. Understanding the EPC calculation: primary energy

The EPC score does not just measure your actual consumption, but your consumption of primary energy. For electric heating (heat pumps), Belgium applies a conversion factor.

• Gas or heating oil: For 1 kWh consumed, the EPC counts 1 kWh of primary energy.
• Geothermal: Thanks to a high COP (coefficient of performance), often above 5, your system produces 5 kWh of heat for just 1 kWh of electricity.

The EPC software recognises this exceptional efficiency. Installing a 150-metre probe can cut the "heating" share of your certificate by a factor of 4 or 5 compared with a modern condensing boiler.

2. Geothermal vs air-source in the EPC software

Many energy assessors and architects will confirm it: with the same insulation, a house with a geothermal (ground-to-water) heat pump systematically scores better than one with an air-source (air-to-water) heat pump.

• Stable source temperature: The software penalises air-source systems because their efficiency drops in freezing weather. Geothermal, with its stable 12 °C source at 150 metres, gets a performance bonus in the calculation.
• Auxiliary consumption: No power-hungry outdoor fans and no energy-intensive defrost cycles reduce the "hidden" consumption the assessor takes into account.

3. Geocooling: comfort without a penalty

One of the EPC's pitfalls is air conditioning. If you install conventional air conditioning for summer, the software treats it as extra energy use and lowers your score (overheating risk).

• The positive loophole: Passive geocooling uses so little energy that the software considers it negligible. You enjoy a cool house all summer without your certificate turning from green to orange.

4. Reaching an "A" or "A+" rating

For new builds or deep renovations, an A rating is the ultimate goal. It is almost impossible with gas, and difficult with a simple air-to-water heat pump without a massive number of solar panels. With WellDoneDrill, geothermal does most of the work. It reduces primary energy needs so much that a small solar installation is often enough to tip the house into the energy-positive category.

5. An investment that pays off on certificate day

Picture a 200 m² house. Going from a C to an A rating can mean a market value difference of €40,000 to €60,000. The cost of your borehole (about €15,000 to €20,000) is therefore paid back immediately by the increase in property value, before you have even saved a single euro on your first heating bill.