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Tools and calculators to make radiator sizing simple

Getting radiator sizing right is critical to ensuring rooms are warm and comfortable without wasting energy. With many factors to consider, sizing equations and calculations can be tricky. Proper sizing requires a lot of information, from room layout and fabric to water temperature and heat source type.

  1. Rads and Towel Warmers
  2. Product info
15 Oct 2026

Myson’s online calculators make the process simple. The Room Heat Loss Calculator accounts for metrics such as temperature, placement and insulation, giving a clear indication of the amount of heat loss a radiator must account for.

There’s also a range of sizing calculators aligned specifically to Myson’s extensive product range. So whether you’re installing a panel radiator, a designer radiator, an electric radiator or a towel warmer, you can accurately gauge the right size for the space in just a few clicks, avoiding common mistakes such as:

  • Guessing the size

    Choosing a radiator based on the way it looks, or the available wall space, instead of calculating thermal requirements frequently leads to poor thermal performance.

  • Ignoring insulation and windows

    Failing to account for insulation, single versus double glazing, and whether cavity walls are insulated can all lead to underheating.

  • Overlooking ceiling height

    Making calculations based on floor area instead of total room volume will leave rooms with high ceilings underheated.

  • Relying on a single unit for large spaces

    Trying to heat a large room or open-plan space with one large radiator can create uneven heat distribution and cold spots. It might be more effective to split the necessary output across multiple smaller emitters.

  • Ignoring heat pump requirements

    Heat pumps run on lower water temperatures and require their own sizing considerations. Radiators typically need to be larger to provide the same output as traditional boiler systems.

  • Oversizing the radiator ‘just in case’

    This forces short, inefficient heating cycles where the system turns on and off repeatedly, which wastes energy and wears out components.

Accurate sizing takes the guesswork out of radiator selection and helps ensure the heating system performs as intended. Myson’s calculators give installers a quick and practical way to work out the right radiator for the job.

Explore Myson’s calculators or contact the Myson team for further support.