How To Choose The Right Size And Quantity Of Radiators

In order to heat any room in your house efficiently, you need to ensure you choose the right size and quantity of electric radiators.

If your radiator is too small and not powerful enough, you’ll be spending more money on electricity than you need to, and still have a cold room. If your radiator is too large, you’ll be spending more money than you need to upfront on the radiator itself and might struggle to fit it in the right place.

Working out the size of radiator you need

The radiator size, wattage and quantity you need will depend on two things:

  • The size of the room (including ceiling height) - the bigger the room, the bigger the radiator you'll need
  • How well insulated the room is - the poorer the insulation, the bigger the radiator you'll need

If you're looking for a rough rule of thumb, there is a generally accepted correlation between required wattage and room size in square metres. If yours is a poorly insulated room, you need 100 watts per 1m2.

On our price list page, and on individual radiator pages, you’ll find a table that outlines the following:

  • Radiator wattage
  • Suitable room size in square metres - both poor and modern insulation
  • Radiator dimensions
  • Radiator weight

For example, the table below shows the available specifications for our Vertex Compact electric radiator:

Wattage Room Size M2
InsulationPoor / Modern
600 6 7 565 486 73 8
900 9 11 565 648 73 10
1200 12 14 565 810 73 12
1500 15 18 565 972 73 15
1800 18 21 565 1134 73 18
2100 21 25 565 1296 73 20

So, if the room you’d like to heat - your living room, for example - is 11 square metres and insulated to modern standards, the 900 watt 600 x 622mm Vertex Compact radiator will meet your needs.

What is 'modern insulation'?

When we refer to a room with 'modern insulation', we mean one that is cavity wall insulated, double glazed, loft insulated to current regulations (if applicable) and one from which there is no excessive heat loss from a number of drafty doors or windows. If yours is a relatively modern property, it will most likely be well insulated.

Poor insulation is common in older properties. By 'poor insulation', we mean rooms with no cavity wall insulation, single glazing and/or lots of windows and doors through which heat can escape.

If your room is poorly insulated, a more powerful and larger radiator will be required to compensate for the larger amount of heat being lost.

Ceiling height

For the general recommendations made in tables like the one above, we assume that a standard ceiling is 3.5 metres high. If your room has a high ceiling, for example perhaps yours is a Victorian property, a factor of 1.25 needs to be applied. That means you will need a radiator that is 25% more powerful than someone heating a room of the same size with standard ceilings.

For vaulted ceilings that go up into the eaves, a factor of 1.5 needs to be applied, meaning you need a radiator that is 50% more powerful.

If you’re concerned about how the ceiling height of your rooms impacts the radiator size you need, please don’t hesitate to contact us - we'll happily answer any questions you have.

What if my room falls between two sizes?

If the size of the room you want to heat sits just between two radiator sizes, we recommend that you choose the higher wattage radiator. You'll find that it will heat up your room quicker, reach the programmed temperature and then switch off.

If you choose a radiator that is too small, it will use up more electricity as it works harder to heat the room.

For example, if the room you want to heat is 9 square metres and well insulated, the 900 watt 600 x 622mm Vertex Compact radiator will meet your needs.

When to use multiple radiators

Again, if the size of your room falls between two wattage recommendations, and you have sufficient wall space, it may be appropriate to choose two smaller radiators rather than one large one.

For example, if your room is 14 square metres and well insulated, you may choose to use two 600 watt 600 x 465mm Vertex Compact radiators.

As ever, if you have any questions about how many radiators are best for your room, don’t hesitate to contact us.

Heating different rooms with electric radiators

For different rooms in your home, there are slightly different considerations to be made when choosing the right radiators.


Conservatories are notoriously difficult to heat because of the amount of glass they feature, and the limited amount of wall space available. As such, when choosing an electric radiator for a conservatory, you will need one that is more powerful but also lower in height. For more information, see our guide to heating a conservatory with electric radiators.


Electric radiators or heated towel rails used in the bathroom must meet stipulated waterproof standards and must also be placed in certain ‘Bathroom Electrical Zones’. For more information, see our guide to heating a bathroom with electric radiators.


When heating your kitchen, you need to ensure the radiator you choose is sufficiently responsive to quickly adapt to changing temperatures - for example, when the oven is on. For more information, see our guide to heating a kitchen with electric radiators.

Ultimately, every room in every home is different. The information we’ve provided here should help give you a fair idea of which size you’re looking for, but is intended as a guideline only. If you’ve got any questions at all about which electric radiator is best for your needs, please don’t hesitate to call us on 01845 518 888.

Find out more about The Economy Radiator Company and our electric radiators: