Selecting Heater Size

Convector heaters warm all the air in a space/room. It is therefore very important to choose the correct size heaters for the rooms you require heating. We will assume that your ceilings are normal height (about 2.8 Metres)

Adax, Beha and Vigo all produce size charts, but we find the following rule-of-thumb to work well for non-insulated Spanish houses. 
In a living room you will need 100 watts per m²:  1,000 watts (1kw) per 10m².
In a bedroom you probably only need 75 watts per m²:  750 watts per 10m².

You need to find out the area in square metres of your room. For my example I am going to make the dimensions 7 metres by 3 metres, which is 21m². For ease of calculation let’s call it 20m². This means that if it is a living area you will need 2kw to heat it. If it is a bedroom; 1.5kw will probably be sufficient.

You then have to consider the following factors.

·         The most efficient way to heat a rectangular room, like this, is to have two heaters; one at either end.

·         It is cheaper to buy one 2kw heater than two 1kw heaters.

·         Do you have sufficient wall space to mount your heaters?
(free standing options with Neat Feet are available for all our models)

Other Factors you should consider.

·         Your contracted limit. It is no good buying 7 kilowatts worth of heaters if your contract only permits you 5.5kw. If in doubt consult your supplier, or a qualified electrician.

·         Convector heaters cannot heat half a room. When calculating the area to heat you must always include any open plan areas that cannot be closed off. This includes hallways, stairwells, serving hatches to kitchens etc.

·         Many houses in Spain have high ceilings. These must be included in your calculations.

·         The aspect of your rooms will also determine how cold they get.

Having taken all the above into consideration, if you are undecided between two sizes, you should usually pick the larger option. The difference in purchase price is minimal, and…….

·         The smaller heater might struggle on colder days.

·         The larger heater will take less time to achieve the temperature you require, and turn off for longer periods, so the consumption will be similar.

·         Never pick a smaller heater “Just to take off the chill”. Always pick the correct heater and just turn it down to the required temperature.

Adax and NEO recommended calculations In Norway

Vigo Basic Electric Panel Convector Heater Model Selection


Recommended Heater Power (watt)

Room Area (m2)

EPK 4550 E05



EPK 4570 E10



EPK 4570 E15



EPK 4590 E20



EPK 4590 E25



The heat requirement depends on factors such as the exterior temperature, room heat insulation, door open / close cycles. The values stated on the above table are for average conditions therefore when calculating the heater power these factors should be taken into consideration

Online Beha Heater Calculator
To download, please click here

(Please note that in Spain, Portugal and France most houses are not very well insulated in comparison to Norwegian homes. Please select poor insulation when considering the size of your heater or if in doubt use the 100w for every m2 rule) 


The approximate running cost are 23 cents ( including iva ) per kilowatt hour , based on Iberdrola standard tariff. (rates vary, please check your individual tariff on your electricity bill in your area) 
This means that for every 1 kw used continuously for one hour it will cost you 23 cents.
The total cost for a 1kw heater running continuously for 24 hours would therefore be € 5.52.
(These figures are greatly reduced with the thermostat in operation) 

You can work out roughly how much your heating would be using our heaters the following way.
Work out the square meterage of the room/rooms you want to heat. The chart will show you the size of radiator in Watts that would be needed to effectively heat that room.
Each 100 watts will cost you 0.023 cents including iva per hour on the standard tariff (Iberdrolla´s figures, the correct term is 23 cents /kilowatt hour, it means the same).

The cost is varied by the fact that Adax heaters have thermostats built into them and therefore are not running continuously for one hour as they will be reaching the set temperature and turning off.
The thermostat will also regulate according to differing factors like the outdoor temperature and how many open doors or windows you have in the area where the heaters are fitted.

A heater with a greater wattage does not use more energy, and does not cost more to run. The heater’s element will be working less frequently, which also gives a lower surface temperature.