RESIDENTIAL HEATING & VENTILATION
Practical guidance for delivering lower carbon homes
The 2026 edition of the CIBSE Domestic Heating Design Guide arrives at a time when domestic system design is under growing pressure to deliver lower carbon performance in practice, not just on paper. Mark Krull, director at LCL Awards, which contributed to the revised guide, highlights the areas likely to matter most to installers and designers
H
eat pumps, low temperature emitters, improved fabric standards and changing regulation are all pushing the building
services sector towards a more rigorous design and installation approach. CIBSE’s updated Domestic Heating Design Guide brings together current best practice across heat loss assessment, emitter selection, domestic hot water, controls and commissioning at a time when Warm Homes, the Future Homes Standard and general concerns around energy security due to global unrest, are increasing attention on low carbon systems.
What’s new for 2026:
¡ A stronger focus on accurate heat loss assessment and avoiding oversizing ¡ Greater emphasis on low temperature system design and emitter choice ¡ Updated guidance on domestic hot water, controls and mixed temperature systems ¡ Clearer documentation of system intent and design responsibility
Low temperature design & control
One of the clearest themes in the revised guide is a focus on low temperature heating and hot water systems, such as heat pumps. Coverage of heat emitters has been expanded beyond standard steel panel radiators, with improved attention to core fl uid dynamics, modern hydraulic arrangements, circulator control options and low-loss headers. Advanced layouts, including four-pipe heat generators and manifold distribution, are also featured.
The guide provides dedicated attention to control strategy, including mixed temperature systems. As
22 July 2026
more homes combine diff erent emitters or balance space heating with domestic hot water demand, installers increasingly need to understand how the parts of a system interact. Better controls can support comfort, effi ciency and stability, while helping end users achieve optimum performance. Another important change is the closer
integration of space heating and domestic hot water design. Domestic hot water provision has been updated in line with BS EN 12831-3:2017, with new information on cylinder sizing, including the storage of domestic hot water below 60°C and the associated thermal disinfection procedure.
Heat loss in the spotlight
One of the most signifi cant changes in the 2026 guide is its treatment of heat loss. CIBSE has aligned the assessment method more closely with BS EN 12831-1 and has incorporated updated weather data including 28 zones and four outdoor design temperatures. Heat loss calculations sit at the centre of system
effi ciency - if they are wrong, emitter sizing, fl ow temperatures, plant selection and overall running performance are likely to be wrong as well, leading to unnecessary energy use, higher bills and dissatisfi ed householders. The guide also encourages a more disciplined
approach to safety margins. Rather than adding extra allowance at several stages of the design, the emphasis is on getting the assessment right fi rst and only making adjustments at the end where they are genuinely needed; a step that should help reduce oversizing, which has long limited effi cient low temperature operation. A fabric-fi rst approach is reinforced too, with updated U-value tables refl ecting modern
construction methods and revised guidance on air permeability assessment. Wherever possible, an air permeability test is preferred, while SAP 10 methodology is identifi ed as the fallback for retrofi t work. The overall message is simple: understand the building before sizing the system.
Clearer accountability in design
A notable addition to the guide is the new System Criteria Document. Its purpose is to provide a clear and auditable record of design decisions, system intent and professional responsibility, with the potential to support commissioning and client and designer sign-off in line with the Building Safety Act. Better documentation can improve handover, reduce misunderstandings and make it easier to demonstrate that design choices were made deliberately. In practical terms, better design should mean
fewer compromises on site, more predictable commissioning, improved effi ciency and a stronger case for low carbon systems overall. The CIBSE Domestic Heating Design Guide
informs the content of related qualifi cations, including LCL Awards’ Domestic Heating and Hot Water System Design in Dwellings. By aligning learning outcomes with this guidance, training can help ensure that candidates are able to apply best practice in real-world situations.
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