BUILDING CONTROLS & TECHNOLOGY
Evidence-based insights take the guesswork out of HVAC design
T
This clear shift towards understanding real- world building energy performance means airtightness testing is becoming a vital tool in HVAC design and retrofit strategy, moving us away from ‘best guess’ solutions, towards evidence- based installations. That’s according to Luke Smith, managing director of Build Test Solutions (BTS)
here are a range of tools that can aid understanding about a home’s measured energy performance. Airtightness results from tests, such as Pulse or blower door, are very effective for assessing air changes and the associated heat loss in the form of air leakage pathways and draughts. On the flip side, such tools can also determine the appropriateness of installed ventilation, helping to ensure systems are fit for purpose and avoid damaging effects, such as damp and mould.
The new EPC
At the time of writing, details about the new Energy Performance Certificates (EPCs) are imminent, but the Government has already made it clear the metrics it intends to use to improve understanding about building energy performance. While the current EPC offers merely a cost estimate of a property’s energy bills, the ‘new’ EPC will take a more forensic approach.
Its four headline metrics are expected to be: • Energy cost: a fuel bill estimate, to help people make decisions about which energy efficiency home improvements to make.
• Fabric performance: the thermal performance of a building’s walls, roof, floor and constructed elements, to emphasise how a well-insulated, energy-efficient space is more comfortable to live in.
• Heating system: the building heating source, with information on its efficiency and environmental impact, to speed up adoption of lower carbon heating solutions.
• Smart readiness: how readily a building can have smart technologies integrated, to optimise resident energy consumption and enable them to benefit from cheaper smart tariffs.
There will also be a raft of secondary metrics, starting with two that could potentially grow to include indicators about a property’s health impacts.
• Carbon: the estimated carbon emissions from a building from the energy use of its occupants.
• Energy use: overall energy consumption, as well as potential energy efficiency improvements
By using fabric performance as a metric, this will make evidence-based insights, such as airtightness testing, more important to accurately assess thermal performance.
This new EPC information will support decision making around building fabric retrofit. At the same time, any measured energy performance information used to determine EPC ratings can also be used to specify and size heat pumps and other heating systems more accurately, while also guiding the design and specification of other HVAC installations.
Measured data replaces assumptions
The shift to measured data has already begun. From June 2025, domestic energy assessors have been able to input measured airtightness results into the RdSAP10 methodology, which is used to calculate EPC ratings for existing homes. This new input can bump up the point score by between one and three, potentially increasing the EPC rating. EPC reform brings an even greater need for insight, moving the dial further to reflect real- world property energy performance, rather than relying on assumptions and default values. And while the new EPC will initially be for new homes, this will be rolled out across all buildings to base ratings on live fuel prices, actual home occupancy and energy use, and information about how the specific building is constructed and heated.
The use of airtightness testing also has practical design benefits for HVAC specification and design. Measured data feeds directly into heat loss calculations, with the MCS heat loss calculator now also accepting measured airtightness results. This enables engineers to right-size HVAC systems and avoid over- or under-specification. The result is reduced installation and running costs for residents – one of the most tangible outcomes of the move to data-led design. More widely, measurement can not only
provide the evidence base for retrofit strategy but also provide the data to confirm effectiveness upon completion. Homeowners will be recognised for this work by a more accurate EPC system that reflects the work done.
A tool for compliance and confidence
Under the latest PAS 2035:2023 framework, which delivers guidance for whole-house energy-efficient retrofit, airtightness testing is no longer an optional step – it is embedded into the entire compliance process. Any project involving fabric upgrades – from insulation to window replacements – must include a defined airtightness and air leakage
6 BUILDING SERVICES & ENVIRONMENTAL ENGINEER DECEMBER 2025
testing strategy. Pulse testing, which measures leakage at 4Pa, offers an accurate view of real- world performance. Its results help to shape the fabric upgrade strategy whilst also informing ventilation system design, ultimately ensuring that the retrofit delivers the intended energy savings and occupant well-being and comfort. This performance-led approach aligns with both the 2021 Part L and Part F of the Building Regulations – and the upcoming Future Homes Standard – all further supporting the overall shift towards measured outcomes-based delivery of new and refurbished buildings. Testing verifies that both retrofit interventions and new builds meet design intent, but also provides the evidence needed for funding bodies, auditors and residents alike.
Supporting retrofit funding and social housing bids
For local authorities and housing associations delivering against the Social Housing Decarbonisation Fund (SHDF) Wave 3 programme, airtightness testing has become a strategic advantage. Pre- and post-works test results not only deliver compliance but also provide robust, verifiable data to evidence carbon and energy efficiency gains. In many cases, this level of detail strengthens bids and helps demonstrate clear alignment with national retrofit goals, including improved indoor air quality and reduced fuel poverty. In addition, the SAP score uplift offered by the testing helps to directly contribute towards landlords meeting the Minimum Energy Efficiency Standard (MEES) requirement of EPC C by 2030 across both new and existing tenancies, without unnecessary additional measures.
Performance-driven HVAC design
The combined effect of EPC reform, PAS 2035 and updated building regulations is a new era for HVAC design. Measured airtightness data informs not just compliance but system design, occupant comfort and long-term building health. Retrofit professionals are increasingly expected to demonstrate results, not assumptions. Airtightness testing, combined with ventilation flow rate tests, have the power to demonstrate that retrofit interventions and low-carbon heating installations meet both energy efficiency and occupant health requirements. In short, airtightness is no longer a tick-box
exercise: it’s a key metric shaping the future of low-carbon building performance.
Read the latest at:
www.bsee.co.uk
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36
