You’ve probably noticed: your meter displays cubic metres (m³) while your bill refers to kilowatt-hours (kWh). Don’t worry, this isn’t a calculation error; it’s a method intended to make sure you’re billed as accurately as possible.
This difference, which may seem complex at first glance, is based on a desire for technical accuracy and fairness among consumers. The following are the key points to help you understand how your actual consumption is converted into the amount billed.
Why convert to kilowatt-hours?
Natural gas is a product extracted from the earth, and its composition varies depending on the source. As a result, a one-cubic-metre volume of gas does not always produce the same amount of heat, depending on where it came from. If billing were based solely on volume (m³), some customers would be at a disadvantage, as they would receive gas with a lower calorific value than others.
Using kWh makes it possible to measure the actual energy in the gas rather than the space it takes up. This system ensures that you only pay for the heat produced and the energy you have actually consumed, and not simply for a volume of gas.
The role of calorific value
The capacity of gas to produce heat is known as its ‘calorific value’. Although high-calorific gas is now the standard, the calorific value can vary slightly from year to year. This fluctuation is due to the origin of the gas, its composition, and also factors such as the altitude of your place of consumption.
The energy value of the gas is calculated by your system operator. The latter determines the exact conversion factor based on the quality of the gas supplied to your address.
What is the coefficient in Brussels?
In Brussels, this value usually fluctuates around 11.5 kWh per m³. You can find the monthly values for the UCV (the upper calorific value of gas) here.
The 3 stages of billing
- It all starts with your meter reading: the difference between your new reading and the previous one is the basis for calculating your annual consumption, expressed in cubic metres.
- Once this volume is known, it is converted into kilowatt-hours by your system operator using the conversion factor.
- Finally, this consumption is sent to your energy supplier, who calculates your annual bill (total in kWh multiplied by the unit price per kWh specified in your contract).
A practical example
Let’s take the example of a household with a meter reading 27,000 m³, and displaying 29,100 m³ a year later.
- The recorded annual consumption is therefore 2,100 m³.
- To convert this volume into energy, we multiply this 2,100 m³ by the average value of 11.5 kWh/m³ (for example), which gives a total of 24,150 kWh.
- If your contract specifies a rate of €0.05/kWh, your annual cost for gas consumption will be €1,207.50.
This example perfectly illustrates how the volume, gas quality and your contractual rate are combined in calculating your final bill.
NB: this amount corresponds to the ‘energy’ portion of your bill. To calculate your total cost, you will need to add grid charges and taxes, which can almost double the final cost per kWh.
