Dimplex oil-free or De'Longhi oil-filled radiator?

Which to buy

Pick Dimplex for an hour or two of heat at a time, or a heater you move from room to room. Dimplex says its oil-free ECR warms up as much as 30% faster than a 2kW oil-filled column and uses up to 9% less energy in its own test: heating a room from 10°C to 22°C, holding 22°C for 5 hours, then switching off. The ECR15 weighs about 8.6kg.

Pick De'Longhi for long evenings in one room. De'Longhi says the Dragon 4's heated oil keeps releasing heat for a while after the unit is switched off, and Electrical Safety First says oil-filled radiators take longer to warm up but continue to give out heat afterwards. The Dragon 4 weighs about 14.1kg and rolls on folding castors.

Pick the Dimplex ECR20TIE rather than the ECR15 if you want a timer: the ECR15 has none. The Dragon 4 has a 24-hour dial timer.

Oil-free and oil-filled

Dimplex's case for its oil-free design is the faster warm-up, in its own test; De'Longhi's page points to the way oil holds heat.

Both makers say a portable heater like these suits only well insulated spaces or occasional use, and both have a frost setting for a cold spare room or garage.

Running cost

On the same setting the two use the same electricity. The Centre for Sustainable Energy works out an appliance's use as its wattage times the hours it runs, so a 2kW radiator on full for an hour uses 2kWh whichever brand it is.

What changes the bill is how long the element stays on and at what setting. Both have a thermostat that cuts the heat once the room reaches the temperature you set, and a low setting, 500 or 600W on the Dimplex and 900W on the Dragon 4. Dimplex's energy claim comes from its own test pattern, not from a lower wattage.