Portable Heater Running Costs: Watts, Thermostats and the Efficiency Myth

Start with input power, time and your tariff

Australian Government Energy Ratings guidance uses a portable electric heater as the worked example for appliance running cost:

1. find your electricity price in dollars per kilowatt-hour (kWh);
2. convert heater input power from watts to kilowatts by dividing by 1000;
3. multiply kilowatts by the electricity price per kWh;
4. multiply by the actual time the appliance draws that power.

So a 2000W heater is 2kW. If it drew 2kW continuously for one hour and your electricity rate were $0.35/kWh, the energy component would be about $0.70 for that hour.

The 35-cent rate is only an example. Use the tariff on your own plan rather than a hard-coded PIQSY number.

Maximum watts are not the same as evening-long consumption

The current PIQSY heater set shows why maximum input is only the starting point:

• Dimplex DHCERA15M: 1500W maximum.
• Philips CX3120/01: 900W, 1200W and 2000W settings.
• De'Longhi Radia S: 1000W minimum and 2400W maximum across three settings.
• De'Longhi Dragon5 Connect: 2400W maximum with automatic power modulation.
• Ausclimate ACPH915: 2000W maximum with five heat settings and inverter power modulation.

Those figures do not tell you exactly how many kWh each product will use over an evening. Actual consumption depends on setting, thermostat behaviour and how long the heater remains energised at each power level.

Resistance heaters are 100% efficient at the point of use — that is not the same as cheap

Current Australian Government guidance says electric resistance heaters convert electrical energy into heat and are 100% energy efficient at the point of use: one unit of electrical energy becomes one unit of heat energy.

That statement is often misunderstood.

It does not mean:

• every 1500W, 2000W and 2400W heater has the same hourly cost;
• every heater needs the same run time to maintain comfort;
• insulation, draughts, ceiling height or room size stop mattering;
• an oil column, ceramic heater or panel heater is automatically cheaper because of its format name.

A higher-input heater can draw more power while energised. A thermostat may then reduce the amount of time the element stays on once the set point is reached. The real bill is the accumulated kWh over the period of use.

Thermostats and modulation change duty cycle, not energy-conversion physics

A thermostat can reduce unnecessary heating once the target temperature is reached. Australian Government guidance notes that thermostat settings materially affect energy use and recommends using thermostat controls to minimise energy consumption while maintaining comfort.

Dragon5's automatic power modulation and Ausclimate's inverter modulation are regulation features. Philips offers discrete lower-power settings, while Radia S provides multiple power settings and an electronic thermostat.

These controls can change how much and how long the heater draws power in a given room. PIQSY does not convert labels such as “Eco”, “inverter” or “smart” into a guaranteed percentage saving unless comparable evidence supports that exact claim.

Room heat loss can dominate the bill

A thermostat can only reduce run time if the room can approach and maintain the target temperature.

Insulation, draughts, open doors, ceiling height, window area, outdoor temperature and target set point all affect heat loss. Australian Government energy guidance specifically notes that insulation and air tightness improve heating efficiency, and that thermostat changes affect energy use.

That is why a smaller-wattage heater running almost continuously can be a poor solution for a demanding room, while a higher-input heater does not automatically mean a higher total bill if it can cycle appropriately after reaching the set point.

The correct comparison is actual kWh needed to achieve the comfort target, not wattage in isolation.

Do not confuse resistance heaters with heat pumps

Portable resistance heaters generate heat from electrical resistance. Reverse-cycle air conditioners use a heat-pump cycle to transfer heat instead of generating all useful heat directly from resistance.

Australian Government electrification guidance identifies reverse-cycle split systems as a more energy-efficient heating technology than electric resistance space heating in appropriate installations.

So “all portable resistance heaters are 100% efficient at point of use” does not mean portable resistance heaters are the most energy-efficient way to heat a home compared with heat-pump technology.

Use a two-step running-cost decision

Step 1: estimate the full-power ceiling. Convert the selected power setting to kW and multiply by your tariff and intended hours.

Step 2: ask what will change actual run time. Consider thermostat behaviour, lower-power modes, room heat loss, set point and session length.

This produces a much more defensible estimate than assuming “oil is cheaper”, “ceramic costs more”, or an Eco/inverter label guarantees savings.

Electrical safety still applies

Current Fire and Rescue NSW guidance says heaters should be kept clear of combustible materials, power points and power boards should not be overloaded, and heater guidance advises direct wall-socket use. The running-cost calculation is not a reason to use an unsafe extension or power-board arrangement.