When you're replacing radiators in a ward, school or care setting, the specification must do two things: hold accessible surfaces below 43°C and still meet the room's calculated heat loss. Enclosing the emitter within a casing solves the former. It's the latter, that decides whether the specification works.
A casing adds depth and limits direct radiant transfer to the room, so a cased LST radiator generally needs a larger heat-exchanging surface than an exposed radiator to deliver equivalent output. Protecting the patient is straightforward. Recovering the output, you lose protecting the patient is the radiator design problem.
A cover is not one decision, it's four that interact: airflow path, grille position, high/low convection layout, and internal heat-exchanger sizing.
Get the balance wrong and the failures may include: Starved airflow, cutting output below the figure the room needs. Heat trapped inside the casing, raising the casing's own surface temperature back towards the 43°C limit the cover was fitted for. Tight internal cavities become areas that cleaning schedules can't reach properly.
Which raises the question that decides the specification: how do you verify that a given casing design delivers the desired output?
As Part One covered, BS EN 442 → introduced a standard laboratory test for measuring radiator output. This meant manufacturers could publish figures based on a recognised test, rather than relying on their own claims.
This is why radiator outputs are shown at different temperature differences, such as ΔT50, ΔT30, ΔT24 and ΔT20. Each figure is calculated from the same tested equation, based on the difference between the radiator temperature and the room temperature.
However, these figures should not always be treated as exact. Research published in the REHVA Journal found that, for some radiator types and operating conditions, calculated outputs could differ from directly measured outputs by around 10%. This was particularly noticeable with panel radiators operating at low flow rates and large temperature differences.
This does not mean BS EN 442 is generally inaccurate. It shows that radiator performance can vary under certain conditions. As heat pumps make lower-flow and part-load operation more common, it can be more useful to look at performance data across a range of operating conditions rather than relying on one quoted wattage.
How LST & heat pumps overlap
Heat pumps run at flow temperatures of roughly 35–55°C, against 60–80°C for a conventional gas boiler. Output falls as the temperature difference between emitter and room narrows, so a radiator sized to perform at boiler flow temperatures will generally need to be larger to deliver the same output once flow drops to heat-pump levels. The commonly quoted 1.5–2x figure is a rule of thumb rather than a design value: the actual factor depends on room temperature, flow and return temperatures, the radiator's exponent, and the original design conditions, and needs calculating per installation.
The scale of the retrofit challenge varies depending on how it is measured. A 2021 BEIS survey suggested that around 90% of UK homes would need radiator upgrades to meet peak heat demand at a 55°C flow temperature, rising to around 99% at 45°C. More recent research, based on measured data from approximately 4,600 UK boilers, paints a less severe picture: around a third of homes may already be able to meet peak demand at a 55°C flow temperature without changing their radiators.
Although these studies focus on domestic heating rather than healthcare, the underlying principle is the same: as system temperatures fall, radiators need enough surface area and heat output to meet the room's heat loss.
This creates a natural overlap with LST radiator design. LST radiators have long used larger heat-emitting surfaces to deliver the required output while keeping accessible surface temperatures safer. Where additional output is needed within limited wall space, designs such as Contour's DeepClean Triple Fin LST radiator increase the available heat-emitting surface within a similar overall height to a double-fin model.
That does not mean an LST radiator is automatically suitable for a heat pump. The correct radiator still needs to be selected using its certified output at the intended flow and return temperatures and checked against the calculated heat loss of the room. Looking at published outputs at lower ΔT conditions is therefore more useful than relying on the product category alone.
Surface temperature is a well-defined and manageable specification requirement rather than a live engineering unknown. Current design effort sits on what the casing introduces alongside it.
Cleanability is the clearest. Fixed grilles trap dust and debris in cavities that cleaning schedules can't reach; removable and drop-down panels that open the casing flat address this directly.
Impact and edge-injury resistance, bullnose corners and radius edges, addresses what happens if someone falls against the unit, sitting alongside rather than replacing the anti-ligature fixing requirements covered in Part One.
Antimicrobial finishes are the third strand. Silver-ion technologies such as BioCote are specified on healthcare-grade LST radiators to address the risk that grilles and internal cavities can otherwise harbour bacteria. Contour's DeepClean range has used BioCote technology since 2006.
The sequence that resolves most of these projects:
1. Calculate the room's heat loss at the design conditions for the setting, not the output of the radiator being replaced.
2. Check certified output at your actual temperature regime, using the delta-T table for the flow and return you'll run, particularly if a heat pump is planned now or later.
3. Select casing, cleaning and safety features for the setting — anti-ligature requirements, cleaning access, and impact resistance vary by ward type and change the product, not just the finish.
A safety threshold from the 1990s produced a design discipline that now has to answer to infection control, ligature risk, and low-temperature heat sources at the same time. The specification questions have grown; the method for answering them hasn't changed much.
Next step: send us the room schedule and intended flow and return temperatures, and we'll return an output assessment showing certified performance at your conditions against the calculated heat loss. Send your room schedule here↗
For the regulatory background behind these requirements, read Part One: The history of low surface temperature radiators: how a safety standard reshaped heating design
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