What Are the Standard Radiator Sizes?

Measuring tape

For many years, radiators were all very similar – chunky white horizontal models that came in three sizes. Heating technology has moved on a long way in the last ten years and now there’s no limit to the number of types, shapes and sizes radiators can be bought in.

Standard radiator sizes are no more thanks to the different types – vertical, horizontal, column and trench all fit into different spaces. While size or shape of space no longer needs to be a constraint, it’s likely that your existing radiators, if not installed in the last few years, do fit the previous standards for radiators. These were, traditionally, 700mm x 1400mm at the smallest and 600mm x 2400mm at the largest for horizontal radiators. Vertical radiators came in at 800mm x 600mm at their largest.

Now, the question homeowners and tenants need to ask is no longer “what are the standard radiator sizes?” but instead, “what size radiator do I need?”. Now, radiators can work for you and your space rather than you working around them.

How to calculate the radiator size for a room

Of course, something you’re not taught in school mathematics lessons is how to calculate the radiator size for a room – that is, the size that will optimally heat the space around it (if not constrained by size limitations due to suitable wall space).

Radiator sizes in the UK use measurements based around a heat output calculation called BTU (British Thermal Units). These are sometimes in the metric system and sometimes imperial, so be sure whichever you’re using is consistent throughout your calculations; or you really will need that interdenominational maths know-how!

A BTU measurement demonstrates how much heat a radiator is capable of emitting, and is calculated by measuring the energy needed to heat a pint of water by a single degree. The higher a BTU number, the quicker the radiator can heat the space around it. A standard radiator in a British home can be expected to have a BTU output of anything from 600 right up to 10,000.

To make the radiator work for the space for optimal heating performance, you need the room’s dimensions: both the width and length of the floor space, as well as the length and width of any windows. The latter is simply because this is where the heat is most likely to escape, particularly if you have old or single-glazed windows. These factors must be taken into consideration, as in these incidences, or where there isn’t sufficient insulation in a room, the BTU should be thought of as ‘the higher, the better’.

Radiator size and BTU table

The easiest way to calculate the BTU needed for the room size is to use a BTU Calculator. Whilst there are plenty of old radiator size and BTU tables and graphs available that can give you a rough overview of standardised sizing and power, the Great Rads BTU Calculator automates calculations and can give you a more accurate measurement, quicker. This will mean an accurate and bespoke BTU calculation for the rooms in your home.

To use the Great Rads BTU Calculator, simply enter the info required. This can be done in either metric or imperial measurements. The required details include:

  • Room dimensions
  • Room type (ie. kitchen, living room, utility room)
  • Window type (ie. single-glazing, double glazing)
  • Room exposure levels (ie. sheltered, internal, external, uninsulated).

The result the BTU Calculator will give you is an estimated measurement to the power a radiator would need to heat your room in the most efficient way to a satisfactory and comfortable temperature. In a large room, you may be installing more than one radiator and so this power measurement can be split between the number of radiators being fitted.

Of course, if appropriate wall space is at a premium, you may be unable to meet a room’s full BTU requirement properly. If this is the case you could consider bench heating, trench heating or underfloor heating, either to replace the traditional radiator set-up or to give an extra boost to the heating output it makes to the room.

If you have any questions about BTU calculation or what the BTU of any given radiator we stock is, just drop a line to the Great Rads team. We’re always happy to help guide you and advise pre-purchase (with no obligation to buy!) and if you’re struggling with calculating the appropriate BTU, we’re happy to do it for you from floor plans and dimension information.


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