Proposed compliance metrics for Part L 2020

Government’s Future Homes Standard consultation closed early last month, leaving industry with no doubt that HVAC specification is about to change. One of the biggest changes is the proposal of four compliance metrics for new developments which will impact new HVAC strategies.

With the net-zero 2050 target now set in law and the last Spring Statement announcing a 2025 Future Homes Standard, the 2020 update to Part L was always going to be a milestone in readying industry for a challenging future.

In order to do this, Government have suggested four compliance metrics for new developments: primary energy, carbon emissions, affordability and minimum standards for fabric and fixed building services.

Primary Energy

The Energy Performance of Buildings Directive (EPBD) requires all new buildings in the UK to be nearly zero energy from the 31st December 2020, with building compliance measured through primary energy. The introduction of this metric means that building specifiers will now need to consider energy use and energy origin when providing heating and hot water for new homes.

Primary energy is a reflection of how much raw fuel is used to generate a unit of final energy, from extraction to transportation to use. As such, renewable technologies perform well under primary energy metrics, especially when specified on-site, and will provide designers with compliance benefits under 2020 updates to Part L.

When looking at the primary energy factors, listed in the table below, other technologies which will be beneficial when gaining building compliance also become clear. Gas, extracted from the ground and shipped straight to the gas network, has the lowest primary energy factors compared with electricity and oil.

However, if primary energy was the sole compliance metric, this would have negative effects on the achievement of the UK’s Carbon Budgets, as a low primary energy solution is often not a low carbon one.


Energy SourcePrimary Energy Factor (SAP 10.1)Carbon Emission Factor (SAP 10.1)



Carbon Emissions

This target has been introduced to ensure that progression already made in reducing CO2 emissions in new homes is protected and enhanced, as many of the UK’s existing environmental targets are based on carbon emissions.

Electricity has rapidly decarbonised due to increased renewables feeding into the grid. This means that as carbon emissions targets become more challenging, electrical solutions will increase in specification. This does not only relate to heat pumps, but also to direct electric solutions, such as panel heaters.

As electricity currently has the highest primary energy factor when compared with oil and gas, designing hybrid solutions will allow a design to utilise benefits from different technologies in order to meet each compliance metric. A hybrid system could mean heat pumps and gas boilers or hot water heat pumps and direct electric panel heaters.


High voltage electricity powerlines



The third proposed compliance metric is affordability. This has been introduced due to the benefit that can be gained from specifying direct electrical solutions due to lower carbon factors. The benefits of such solutions, such as direct electric panels, are only realised in operational use when the fabric retains heat within the building.

This metric aims to ensure that such solutions are not used in developments with low fabric performance due to the current high unit cost of electricity. However, research completed using the SAP 10.1 BETA software has shown that where designs comply with primary energy and minimum fabric standards, the affordability target is also met.

Minimum standards for fabric and fixed building services

The final area of compliance that new developments will need to adhere to is the minimum standards for fabric and fixed building services. Minimum U-values have been increased and the fixed building services have been updated to align with the Ecodesign standards, even though manufacturers have been adhering to Ecodesign rules as they have become legally enforceable.

With four compliance metrics proposed by Government, heating, hot water and ventilation strategies will soon need to change as the way we design our buildings evolves. Although some of these metrics may not be new, ingenuity and hybridisation will be essential to meeting them all in the future; especially as we move away from traditional HVAC solutions.


Colourful city apartment building with balconies


HVAC specification under Part L 2020

In our HVAC Specification Under New Regulatory Standards research paper, you can learn more about HVAC specification under the proposed changes for Part L 2020 and what you can do to prepare new strategies for your projects.

Using the supporting SAP 10.1 BETA software for proposed Part L and Part F 2020, this document analyses the potential impact these changes may have on HVAC specification within residential developments; proposing new strategies to help building designers gain compliance.

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Learn more about HVAC specification under proposed Part L and Part F 2020.

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