On National Radiator Day, technical director at Zehnder Group UK Nigel Coston explains how radiator colour can influence heat efficiency, the science behind it, and tips for choosing the best colour for optimal warmth.

“My room is 4m x 5.5m x 2.5m high: what colour should my radiator?” That was a real and on the face of it, quite strange question that we received once from a customer.

But on reflection, do we give colour and finish enough consideration – what colour should a radiator be?

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Many don’t realise – from interior designers and retailers to end users –  the colour and finish of a radiator can impact not only the aesthetic appeal of a room but also the efficiency of the radiator itself.

While it might seem like a minor detail or personal preference, selecting the right finish can actually make a big difference in both heat output and the overall feel of a space.

Metallic surfaces

Let’s start off with the worst finish for radiator performance  – and that is a shiny metallic surface, like chrome or polished stainless steel.

This type of finish effectively kills the radiant output of a radiator – that ‘s the heat effect you feel that’s transmitted as electromagnetic radiation, the same way that the Sun transmits its heat energy.

This typically means  the output is reduced by 15-50% from what it could theoretically produce.

As an example, a 1200 x 600 ladder type towel rail in white would give an output of 670W, but in chrome this drops to 489W, a reduction of 27%.

The convective output (the amount it warms the air) is virtually unchanged and as the metallic finishes are highly conductive, it will feel very hot when touched.

So why do we use chrome and other metallic finishes? – well, typically, in bathrooms, chrome is chosen so that the towel radiator matches the other fittings such as taps and showers.

This is an important consideration for finishes, that they should compliment or match the décor and fittings in a space and is still the case with the latest PVD type finishes such as Brushed Brass and Brushed Stainless Steel.

Matt Black is best

But with system water temperatures reducing through the use of heat pumps and low carbon energy sources, optimising heat output is becoming increasingly important – so what’s the best finish from a heat out perspective?

Well, the opposite of shiny chrome is Matt Black, and indeed this gives the optimum radiant performance whilst convection remains unaffected.

However, the current rise in the number of black and anthracite finished radiators is not driven by performance, but by design trends.

So once again, the finish of the radiator is driven by style rather than performance.

So why is white the most popular colour for radiators? The simple answer is convenience…and cost.

White is seen as neutral and can sit happily in most interior schemes – it is almost a cloak of invisibility and a large radiator can be hidden in plain sight- we become oblivious to its presence through familiarity.

This means that white radiators can be produced in high volumes (white paint or epoxy polyester powder is only cheaper because it is used in higher volumes than other colours) and consequently white radiators can be easily stocked.

In real world terms, the difference in thermal output between a black finish radiator and a white radiator at normal operating temperatures is in the order of 1% or less – and to put that in perspective, the accuracy of the thermal test is +/-2% .  (The differential at higher temperatures does significantly increase due to the Stefan Boltzman Constant and Planck’s radiation Law – but that is another discussion completely!)

Use warm tones

We have determined that the finish of a radiator can affect the thermal output and could be chosen to match a compliment an interior design -or even to be as anonymous as possible – but it can also affect our mood!

‘Warm’ colours such as red, orange and yellow, which are often associated with summer, sun and fire,  can give a suggestion of heat and coziness even when a radiator is not working and this psychology is often useful when helping occupants feel comfortable even when system temperatures are reduced.

Even warm tones of traditionally ‘cold’ colours can imply snugness in a room.

A design trend of leaving the radiator in the ‘as-manufactured’ condition with just a clear lacquer for corrosion protection can suggest a more stark, architectural feel whilst maintaining thermal performance and the radiator increasingly becomes a design statement.

As the use of colour becomes increasingly important it is now possible to have the radiator valves and other accessories colour matched to the radiator, so that it becomes more of an interior enhancement than a utilitarian, purely functional necessity.

To return to the original question – what colour should my radiator be? – well, it can virtually be whatever colour or finish that you want, but it is great that it is being considered.

In the end, choosing the right radiator colour and finish is more than just matching the décor; it’s about achieving a balance between style, function and even comfort.

We are excited to see interior designers, retailers and customers approaching radiators with an eye for design, considering them as essential elements of the room rather than simply functional items.

So, whether drawn to the sleekness of black, the subtlety of white, or the warmth of a bold colour, there’s always a perfect radiator for every room.

It is wonderful to think that the humble radiator can be seen as well as its effects are felt.