Radiant heating – what’s fact, what’s fiction?

Radiant panels

Radiant heating technology has been around for many years, but has only recently become more widely used in commercial, healthcare and educational applications in the UK. Despite its growing popularity, there is still much confusion about how the technology works, resulting in many false assumptions. Kevin Boulter, technical sales engineer at SPC, examines the most common misconceptions and busts some myths along the way.

  • Radiant panels are the same as radiators

This is false because they use different methods of heat transfer.

Radiant heat is a form of electromagnetic radiation, falling between visible light and radio waves on the electromagnetic spectrum. As part of the spectrum with a long wavelength, it works similarly to the way the sun heats the earth, penetrating clean air without energy loss or deterioration, exchanging heat with any object of a lower temperature. The objects then warm up the air around them.

Radiators, on the other hand, heat a space by convection. This is the transfer of heat from one place to another by the movement of fluids – and so, in heating spaces, convection heats the air first, which in turn heats the objects and people in contact with it.

  • Heat rises, so heated ceiling panels don’t work as well as floor and wall-mounted heating

This is untrue for two reasons.

Hot air rises, but radiant heat uses radiation which can radiate in all directions, including downwards. To give one simple example, the sun’s radiant heat reaches us on earth after travelling more than 90 million miles. Although radiant panels are not as powerful, they work in the same way, sending heat to occupants and objects in a room from heights as great as 30 metres.

Secondly, underfloor heating is not as efficient. Heat resistant floor coverings, such as certain carpets or wood, can significantly reduce the amount of energy that penetrates them. Radiant panels aren’t muffled in this way.

  • Radiant panels warm up objects rather than a space, so they are not as comfortable for occupants

Again, not true. To keep occupants comfortable, it isn’t necessary to heat great volumes of air around them, and it can waste energy to do so.

Depending on which areas of the room and the air that’s being heated (determined by factors including the fabric of the building), relying on space heating can prove inefficient and costly. Conventional (blown air) heating systems allow heat to collect in areas where it is more likely to escape, so that achieving a comfortable temperature can be difficult. One of the key advantages of radiant ceiling panels is that heat can be directed to the interior of the space, reducing or eliminating excessive temperatures on outer walls and ceilings.

  • It’s difficult to control and adjust room temperature if radiant panels are used for heating

Not if a black bulb temperature sensor is used.

A conventional room thermostat doesn’t detect radiant heat, giving a figure around three degrees below the perceived temperature in a room where radiant panels are used for heating. In contrast, a black bulb sensor can measure radiant temperature present as well as air temperature to give a more accurate reading. This means that the heating system can better adjust its output to meet the temperature needs set by users.  In addition, radiant panel heaters are very responsive because they have much lower water volumes than conventional systems.

  • Radiant heating panels at ceiling level make your head hot

This is untrue provided that the layout, surface area and height of the panels have been designed and specified correctly in relation to water temperatures going through the pipes.

As an analogy, think about good lighting design. In general, the light sources should consider the height of the space, and be evenly spread across the ceiling to achieve an even distribution of light. Installing an intense light in a space with a low ceiling would create an uncomfortably bright area underneath, whilst the rest of the room remains under-lit.

Radiant heat works similarly to light. If you put a panel which is too large or too hot in a low ceiling, occupants underneath could feel too warm. In healthcare applications such as hospital wards, the height of patients’ beds particularly needs to be taken into consideration when designing a radiant heating system. For example, a hospital bed usually sits at 1.2m above the floor. If the ward has a typical ceiling height of 2.5m, a static hospital patient would potentially be 1.3m below a radiant panel. To avoid overheating patients, the panels’ surface area, positioning and/ or water temperatures running through the pipes will need to be carefully designed.

Radiant panels which are installed within or hanging from a ceiling free up wall and floor space. In a hospital, this enables more beds and medical equipment to be fitted in wards, whilst more pupils can be accommodated in a school.  With the added benefit of energy savings and easy maintenance, radiant panels are giving conventional heating methods a run for their money.