Low-wattage wall-mounted flat-panel heaters are heavily promoted as being cheap to run and there are several makes on the market.

Most flat-panel heaters deliver around 400W of heat, although other wattages are available. They're usually mounted on 4 spacers to keep them away from the wall. Some have timers as well. They’re cheap to run. At current electricity prices, a 400W flat-panel heater costs 9.2 cents an hour to run ($2.21 per day if left on for 24 hours).

Low running costs are one thing … but do they do a good job of keeping a typical bedroom warm? To find out we tested a 400W flat-panel heater against a dehumidifier and a 2300W thermostatically-controlled oil-column heater.

Our test

We tested an Econoheat 0603 400W flat panel heater, a DeLonghi CF08M dehumidifier and an Evantair TWNDB1EIII-11T 2300W oil column heater.

We tested them in a special "room inside a room". The inner test room was a typical size for a bedroom (3 metres by 4 metres and 2.4 metres high). It had insulated ceilings and walls.

Before the start of each test run, both the inner and outer rooms were stabilised at 8°C. Throughout the test runs – while the inner room warmed up – the outer room was maintained at 8°C. We monitored the temperature of the inner test room with 72 evenly placed sensors.

Dehumidifiers and heating
It may seem strange to use a dehumidifier to heat a room. But dehumidifiers deliver more heat to the room than they use in electricity – so they warm and dry the air. For a fuller explanation see our dehumidifiers test.

What we found

The fastest at heating the room was the oil-column heater – it took only 8.2 minutes to raise the room temperature by 2°C. Almost as fast was the dehumidifier at 8.8 minutes. But the flat-panel heater took 21 minutes to heat the room even by this modest amount.

The World Health Organization (WHO) recommends that bedroom temperatures not drop below 16°C. So we set the thermostat of the oil-column heater to 16°C and waited to see how long it took to get there. It did it within an hour – and then the thermostat cycled on and off to maintain this temperature for the remaining hour of our test run. It used 45 cents worth of electricity over the 2-hour period.

Over a 24-hour period the oil-column heater would cost $5.36 in power but provide a much better level of heating than a flat-panel heater. If used overnight for 12 hours, it would cost about the same as a flat-panel heater running for 24 hours.

How did the dehumidifier and the flat-panel heater compare?

The dehumidifier initially raised the temperature quite quickly but tailed off, giving a final temperature of 11.6°C at the end of the 2 hours. The dehumidifier used 11 cents worth of electricity over the 2 hours (which shows that it’s a cost-effective way of providing a relatively small amount of heating).

The flat-panel heater slowly raised the temperature to 12.2°C after 2 hours and used 19 cents worth of electricity.

Our graph shows the relative performance of each of the heating options.

Tip: You can check the temperature of your room with an inexpensive digital room thermometer. They’re available for less than $20.

Our view

• Our test shows that low-wattage heaters can only do so much – and our test room was well-insulated, unlike many homes.
• To achieve the WHO-recommended temperature of 16°C for bedrooms, a higher-wattage but thermostatically controlled heater is a better solution – even if it costs more to run.
• A dehumidifier is a cost-effective way of warming and drying a room, particularly when it’s used with a thermostatically controlled electric heater.