Calculate heating cost from electrical input and equivalent operating hours, then compare the comfort task being delivered. A room heater and an electric blanket heat different things. Comparing their watts alone does not establish that one can replace the other in every situation.
Two explicit electricity scenarios
| Assumed routine | Daily electricity | 30-day energy | At illustrative R3.50/kWh |
|---|---|---|---|
| 2 kW heater at full input for 3 hours/day | 6 kWh | 180 kWh | R630 |
| 0.1 kW blanket at full input for 3 hours/day | 0.3 kWh | 9 kWh | R31.50 |
The blanket scenario delivers local warmth, not the same room-heating service. Thermostatic cycling and selected settings can reduce actual input from a continuous full-power assumption. Use the model's own instructions and rating.
Use measured consumption or actual run time
Enter watts and equivalent full-power hours in the calculator. If a thermostatic appliance is connected for six hours but the element draws full input for only part of that period, do not silently substitute six full-power hours.
A suitable energy measurement over representative use provides a firmer basis. Record room conditions, settings, occupancy and how long the appliance is actually used. A short test in a warm room does not describe a cold winter evening.
Compare the same useful task
When comparing two room-heating appliances, consider the same room, desired conditions and period. Different technology and controls can change how electricity delivers useful warmth. A low-wattage device used much longer can consume more than the simple wattage comparison suggests.
For personal warming, follow the manufacturer's instructions for the specific product and user. Do not use a blanket or heater outside its intended application to reproduce an example. Keep appliance condition and safe placement separate from the arithmetic.
Winter energy and the household tariff
An extra 180 kWh/month can move a household into a higher energy block where one applies. It is not always correct to multiply every unit by the first-block price. The calculator's named block tariffs accept a baseline for the rest of the month's electricity.
Use the tariff hub to identify the assigned rate. Fixed charges or arrears can also alter a purchase receipt, but they are not physical heater consumption. Compare kWh over the same month before attributing a whole bill change to one device.
A useful heating record
Keep a short log of the input setting, operating hours and measured energy over comparable days. Note other changes such as more hot-water use or different occupancy. If you change one routine, measure again before extrapolating a saving across the whole season.
Prioritise the loads your evidence identifies. Avoid dismissing all small loads or assuming every large appliance dominates every household. The household guide combines the individual estimates.
Heating questions
Does a thermostat change the rated watts?
It can change the proportion of time an element is energised. Calculate actual or equivalent full-power operation, or measure kWh.
Is the monthly figure a winter average?
No. It is a stated scenario. Use your own hours, measured consumption and tariff.
Method reference: Eskom household guidance. Reviewed 1 November 2026; examples use explicit assumptions.