Which electricity price should you use for heating costs?
The price entered in a heating calculator affects comparisons between heat pumps, pellets and electric heaters. First decide whether you want the extra cost of heating or the total cost of your household electricity bill.
1. Find energy use and the unit price
Portuguese bills distinguish energy, contracted power, taxes and other charges. Check the billing period, kWh and whether readings are actual or estimated. A correction for earlier estimates or an additional service can distort a single month. ERSE explains the bill components in Portuguese.
Find the €/kWh line and applicable discounts. Check whether network access is already included before adding another component. Account for applicable variable taxes without double counting. Where VAT rates or thresholds differ, the next kWh may cost a different amount from the previous average. Ask your supplier for a breakdown if needed.
2. Separate additional cost from the whole bill
Consider a made-up bill: 300 kWh, €66 of variable charges and €14 of other charges, totalling €80. The whole-bill average is about €0.267/kWh. The variable average is €66 ÷ 300 = €0.22/kWh.
If heating adds 100 kWh at €0.22 each, the additional energy costs €22. Using the whole-bill average would produce €26.67 and allocate part of the fixed charges again. The €14 is an illustrative assumption, not a statutory charge or a market offer.
If installing heating requires higher contracted power, the increase in the fixed charge is an additional cost of that decision. Budget for it separately. ERSE’s contracted-power simulator considers simultaneous appliance use; monthly kWh alone do not determine the required capacity.
3. Weight time-of-use prices by heating energy
Use the share of heating kWh in each period, rather than the share of calendar hours. With illustrative final prices of €0.16/kWh off-peak and €0.25/kWh otherwise, and 60% of heating energy off-peak:
Weighted price = 0.60 × 0.16 + 0.40 × 0.25 = €0.196/kWh
100 kWh costs €19.60. If only 20% is off-peak, the average becomes €0.232/kWh and the cost €23.20. Check the actual schedule in your contract. These figures are calculation examples, not supplier quotations.
4. Test a plausible price range
If the timing is uncertain, run the calculator at a low, central and high price consistent with your contract. Keep the heated area, hours and efficiency unchanged. You can then see how sensitive the comparison is to the tariff.
WattRumo accepts one electricity price. It does not reproduce a tax bill or every interval of an indexed tariff. Enter a suitable weighted average and budget fixed charges separately. For whole-contract comparisons, use the ERSE energy price simulator.
Check before comparing
- Enter euros per kWh, rather than cents or a daily charge.
- Apply taxes consistently across alternatives.
- Separate energy costs from purchase, installation and maintenance.
- Use prices relevant to your heating schedule.
Next, record heating consumption for a week. A suitable price improves the estimate; it does not measure how much energy your home uses.