After a small change the next energy bill is lower. That is pleasing, but on its own it does not yet prove a specific saving effect of the measure. Perhaps the period was shorter, the weather milder or the dwelling occupied less often. A personal comparison becomes more helpful when these influences remain visible.
Separate consumption and bill
Start with the actually recorded energy quantities and their units. Monetary amounts can additionally be affected by prices and billing items. A lower payment is therefore a different observation to a lower consumption. Also check whether the value was read or estimated and which data mark the start and end of the period.
Our editorial recommendation: transfer the original information unchanged into an overview. Add conversions as separate calculation steps, rather than replacing the original number. Different energy carriers are not treated as equivalent quantities without an explained basis.
Note simultaneously changed conditions
Write down what changed alongside the planned measure: heated rooms, presence, desired room temperature or further technical interventions. Also note if you can no longer reliably reconstruct a datum. Such gaps are more honest than a subsequently tailored memory.
For the weather influence there are meteorological comparison metrics. GeoSphere Austria provides climate indices, including heating degree days. [GEO] An appropriate location and period as well as the meaning of the respective dataset must, however, fit the question. The article does not adopt a current index value and does not provide a blanket formula for individual weather correction.
Separate observation and causal statement
You can first state reliably which consumption was documented for which periods. Whether a measure caused the difference and by how much is a further question. With several simultaneously changed conditions this share cannot be cleanly isolated from two calculations alone.
The result can nevertheless be practically useful. You can determine that the observed trend deserves further monitoring or that data are missing before a specialist discussion. An openly limited statement is more helpful for later decisions than an apparently precise savings rate.
Example: New controller and unoccupied study
A household changes the control and at the same time does not use a study for several weeks. The documented total consumption falls. The overview therefore lists both changes and the respective periods. For an assessment of the controller the entire difference is not simply attributed to its effect.
Prepare the next measurement phase better
Set a comprehensible next recording date and note important usage changes promptly. Device or system settings should only be changed within the permissible scope for that; technical interventions belong in expert hands. If you wish to decide on a larger investment, pass consumption data and context together to a suitable energy advisory service.
In the end there is no proof from two numbers, but an understandable course: measured quantity, period, known influencing factors and open cause. With exactly that a professional can more precisely assess which conclusion already holds and which additional data basis would be sensible.