Stelrad reports on the Energy House 2.0 data and explains why we’re not saying goodbye to radiators anytime soon.

Research providing information on the performance of a large collection of different heating systems present in the Future Homes test houses at the Energy House 2.0 facility at the University of Salford, has provided clear evidence that new homes heated by radiators have lower running costs than those heated by a combination of underfloor heating and radiators in the same building. This where a modern renewable heating system is the source of heat for heating and hot water in the home.

Application of heat pumps in new builds can lead to the default adoption of UFH downstairs with radiators upstairs. However, this latest evidence suggests that the use of radiators throughout a new property offers significant benefits where heat is provided by an air source heat pump rather than a traditional boiler.

The academics responsible for the research are Richard Fitton – Professor of Building Performance, Grant Henshaw – Energy House Research Assistant, William Swan – Professor, Phil Clark, David Farmer – Research Fellow, Anestis Sitmalidis and Xinyi Zhang.

The houses at the Energy House 2.0 facility were built by Bellway Homes and a partnership between Saint Gobain and Barratt Developments. The report follows up on one published in 2023 on the fabric performance of both of these homes.

The systems were selected, designed and installed by the housebuilders and their partners. The research team had no input on the design of these systems and were focussed only on the measurement of the performance of these systems, which number 28 in total, and covered a range of technologies including, infrared heat panels and air source heat pumps (floor mounted and roof mounted). Different heat emitter technologies were also tested including underfloor heating, skirting board heating and importantly for Stelrad, radiators.

All methods of heating the home were measured in the same chamber conditions reflecting typical (5 °C) and more extreme (-5 °C) winter temperatures found in the UK. This allows for a comparison between these technologies that up to this moment has not been possible and represents unique research.

Interestingly, systems with radiators throughout – on each floor – showed lower running costs than the systems with a combination of UFH and radiators. This was not focused on in the report but can be unambiguously calculated from data published within it.

Using the external ASHP with radiators throughout, the running cost was 11% less than with UFH. Using the loft ASHP with radiators throughout, the running cost was 13% less than with UFH. These outcomes are very revealing and highlight the running cost benefits of selecting radiators throughout a new home powered by an air source heat pump of any design.

Radiators throughout a home were shown to be consistently more cost effective than UFH and radiators combined when looking at the most realistic scenario ie a SAP intermittent heating pattern, at average winter temperatures. Out of all 28 tests carried out and researched, the most economic configuration was the external ASHP with radiators throughout running the SAP pattern in a 5 degrees °C environment.

Analysis of other heating regimes tested indicated that if constant 24 hour heat is required then ground floor UFH has the lowest running costs. However, this is shown to be 25% to 35% more expensive than the standard SAP heating pattern with radiators throughout the home. In the overwhelming majority of homes, heating is targeted at times when it is required – not on 24 hours a day. Radiator based systems are clearly better suited to this. They are more responsive than UFH, more flexible and cost effective.

The ability to target heat is very simple with radiators via a locally mounted TRV. Temperature control is intuitive and simple. No external wiring, controls or configuration are required.

A popular function of heating controls is the one-hour boost. It’s a simple way of countering a cold snap or quickly raising the temperature outside of the normal occupational routine. It is also the ‘go to’ control method for those who find modern controls confusing or who are trying to control costs. Radiator based systems are the best solution in all of these cases.

Due to the high thermal mass and low response times of a UFH system, the user is committed to heating for longer periods, potential expensive repairs and restricted floor covering options. It is fundamentally suited to constant heating but in real world situations it lacks flexibility and it is therefore less economical for the majority of households.

“This research confirms our understanding that radiators are the optimal choice when it comes to heating economically and flexibly,” says Tim Wells, Stelrad’s Engineering Manager. “It’s particularly reassuring that these results were achieved in an environment optimised for UFH. We can be confident that radiators are just as fit for the future as they have always been, whether the heat is provided by traditional means or renewable technology.”

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The latest electric radiator series launched in the UK and Ireland by Stelrad has sparked significant interest in the heating sector.

The range is currently made up of 13 expertly selected steel and aluminium radiators and towel radiators. The Electric Series come with a five-year warranty on the heating parts and a two-year warranty on the electric components.

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Chris Harvey, Head of Marketing, Stelrad Radiator Group, explores the relationship between heat pumps and radiators.  

The arrival of the low temperature heating system has brought with it perhaps understandable questions to which specifiers, architects and housing designers want answers. Can we still use products we use now with traditional boiler driven heating systems if the heat source is a heat pump? Is there anything we need to consider that we take for granted nowadays?

The development of lower temperature heating systems, utilising renewable heating appliances such as air source heat pumps, has given rise to a number of questions including, where do components we have got to know and love over the years fit into the future of heating? Stelrad Radiators has responded forcefully to those people who claim, for example, that underfloor heating is the only or ‘best’ solution for heat pump installations.

Well understood
More than 90% of all heating systems in the UK currently rely on radiators to share the heat around the home, and despite the arrival of underfloor heating there is still a marked reluctance to use UFH upstairs in new build and it can be a complex option to fit as a retrofit solution – so radiators tend to win out most of the time. Radiators heat up and cool down far more quickly than underfloor heating, something that needs to be borne in mind when selecting the best way to share heat around the home.

Remember radiators are poorly named. Most radiators are actually convectors – there is a small amount of radiant heat from the radiator but more than 80% of the heat is convected heat – drawn up behind the radiator where the air passes over the metal surfaces of the radiator and heats the air in the room.

In new build housing, using a heat pump-based solution is a relatively simple solution. The heating system can be designed into the home at the outset so you know the parameters in which the heating system has to operate – the method of construction, the size of the rooms, the number, type and size of doors and windows – so the heat loss calculations can be done up front and radiators sized accordingly. 

The key to radiators operating well in any situation is to size them properly at the outset, which involves accurately working out heat loss calculations to achieve the necessary number of BTUs required to provide comfort heating in each room and to select a radiator can provide that level of heating.

In replacement heating systems for older properties there are additional issues. It’s a fact that simply replacing a boiler with a heat pump will usually see the existing radiators unable to provide the levels of heat needed in a home. 

So what is the solution – one that is cost effective and straightforward? Do we need to ditch radiators altogether and look for alternatives?

Larger surface areas
The simple answer is no. Radiators will work well with heat pumps, but you will need to increase the size of the radiators to provide a larger metal surface area to heat the air in the room to the level required to provide comfort heating. This need not involve unsightly radiators – for one, modern radiators are aesthetically far more attractive anyway, but there are other solutions too. 

You can achieve the extra boost radiators need by replacing the existing single or double panel radiators with the relatively new K3 radiators that have three panels and three sets of fins – providing the additional metal surfaces you need but without increasing the radiator footprint on the wall.

Major radiator manufacturers such as Stelrad have anticipated the significant move towards air source heat pumps in the UK and have added new, larger size radiators to their portfolio providing that option. They have also stepped up the options on the K3 radiator designs available too.

Go vertical
In addition, the huge popularity of vertical radiators has also offered a solution. Vertical radiators clearly have a smaller horizontal footprint than a traditional radiator, but they can be larger by design – taking up floor to ceiling space. It may be more practical and more attractive to have two modern vertical radiators in a room than one large standard radiator which traditionally has been placed along under the main window.

Stelrad has developed a wider range of vertical radiators, adding a huge number of new designs and sizes helping to provide the larger radiators needed by the renewable heating options. These take up a much-reduced horizontal footprint to slot into smaller wall areas in a room, to provide the levels of heat required without taking up large wall areas that will cause confrontation with furniture in the rooms. Vertical radiators can be focal points in the room, part of the décor, and fit nooks and crannies in a room which traditional horizontal radiators won’t do as effectively.

So new low temperature heating systems offer additional opportunities for the products we know and love and have used virtually every day of our working lives, for years. There’s no need to change what we do, just an element of changing how we do it, and the questions we ask when undertaking an installation or specifying for a heating system design.

Radiators are very much ‘fit for the future’ but as always, correct sizing will need to be undertaken to ensure that they keep the home warm and cosy. But can radiators work well with air source heat pumps? Very definitely yes they can – and they already are in a host of installations across the UK.

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The latest addition to the growing Stelrad Radiator range is the Silhouette with versions now available in the Vita and Softline Series.

The Silhouette features sophisticated vertical lines on the fascia creating a crisp, clean, bold appeal. The Vita has flat grille and side panels whilst the Softline features gently curved side panels and grille.

Silhouette is a step up from the standard Compact models, but remains an entry level premium panel option for those looking for something a little bit more special than a standard panel radiator. The company reports that it is already proving a popular introduction for housebuilders keen to offer their customers a step up from ‘the norm’ – in radiator parlance.

“It’s a welcome addition to both the Vita and Softline Series, adding a smart new vertical lined fascia to the existing options,” said Head of Marketing Chris Harvey. “It was always envisaged that the Vita and Softline Series would grow in options, and this is the next step in the evolution of these Series that have taken the heating sector by storm, since their launch a couple of years ago.”

PHPD caught up with Stelrad to discover the design options now available for radiators.

The Silhouette is available in 40 different models in K1 and K2 formats, in heights 300 to 600mm and lengths from 400 to 2,000mm and comes in white as standard from stock. It has outputs from 235 Watts (802 Btu/hr) up to 3202 Watts (10,925 Btu/hr).

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