Social Housing

Social housing landlords face constant government pressure to meet and improve on sustainability targets. The added strain of rising energy prices has seen centralised boilers and district heating schemes become increasingly popular in multi-dwelling residences. A highly efficient, centralised heat source helps buildings meet sustainability initiatives, such as the GLA’s ‘Be Lean, Be Clean, Be Green’, and other building regulations. The integration of Combined Heat and Power (CHP) plant within the system further improves the building’s energy efficiency.


Heat Interface Units (HIUs), located within apartments, are integral to the centralised boiler approach. They connect the space heating and domestic hot-water systems to the central boiler network and provide control functions, control devices and measure heat consumption.


Sales of HIUs have grown 85% between 2012 and 2017, from under 25,000 units in 2012 to nearly 45,000 in 2017.  This is still only a small proportion of the 1.6 million domestic boilers sold annually in the UK. With the Zero Carbon Policy coming into force in 2020, district heating and HIUs could be seen in up to 20% of all new build residences in the UK, with forecasts for 100% in multi-dwelling high rise buildings.




There are several benefits to landlords and property managers.

  1. Centralised systems do not require gas distribution to each flat. This means easier maintenance, less safety checks and lower fire risk.
  2. One boiler is contained in a single plantroom not in each dwelling. Engineers and facilities management can carry out maintenance and gas safety checks more easily.
  3. The heat distribution system is more efficient compared to individual boilers in each apartment.
  4. Energy efficient CHP units can be easily integrated.




Complex Billing

The landlord, rather than the utility company, bills the tenant. Third party operators offer landlords a site-wide billing solution. Billing systems must be identified by the design team and included early, as changing the billing provider may require infrastructure changes. The HIU and internal controls chosen will need to interface correctly with the billing system.


Uncontrolled Heat Dissipation

Pipework distributed through communal areas can overheat. Pipework distribution and corridor ventilation require careful planning during the design to limit overheating in common areas.


Product Quality

Not all HIUs are made equal. Some are less intelligent and harder to control, which can affect performance. Simple models are easier to maintain and most of the internal consumables are readily available to a good plumber. More sophisticated units give the user greater control and can be remotely operated and faults diagnosed via a data link. However, these units require a manufacturer’s approved engineer to maintain them, and use more specialist consumables.


Customer Experience

Depending on the controls of the unit the time taken to deliver hot water to the tap from the HIU may differ significantly between units. The delay may not meet the customers’ expectations for instant hot water.


In conclusion, HIUs and centralised boiler systems provide energy efficiency to multi-dwelling buildings. However, models, manufacturers, third-party billing options and pipework distribution must all be determined as part of the new building’s design. The sooner the kit has been identified and integrated into the design, the greater the benefits to the landlord, building manager and residents.


Steven Norwood is Associate Director at Crofton. He leads a team of building services engineers from our London Bridge office.


Crofton offers electrical, mechanical, structural and civil engineering design consultancy. Our multi-disciplinary teams have experience across sectors. Our offices in London, Kent and Sussex serve clients across the South-East.

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