Carbon Emission Factors 2026

The 2026 NCM introduces updated CO₂ emission factors and primary energy factors for all fuel types. The most significant change is the reduction in the grid electricity emission factor from 0.233 kgCO₂/kWh (Part L 2021) to 0.136 kgCO₂/kWh – a 42% reduction reflecting the continued decarbonisation of the UK electricity grid. This single change is the primary mechanism driving the shift to electric heating under the Future Buildings Standard (NCM Modelling Guide, Section 7.1).

CO₂ emission factors by fuel type

The following table shows the standardised CO₂ emission factors used in the 2026 NCM to convert delivered energy (kWh) into carbon emissions (kgCO₂) (NCM Modelling Guide, Section 7.1):

Primary energy factors by fuel type

Primary energy factors account for the total energy consumed in extracting, processing, transporting, and converting each fuel. They are the second metric in the dual compliance test – a building must pass on both CO₂ emissions (BER ≤ TER) and primary energy (BPER ≤ TPER) (NCM Modelling Guide, Section 7.2):

Grid electricity has the highest primary energy factor, reflecting generation, transmission, and distribution losses. The dual metric (CO₂ + primary energy) prevents gaming – a building cannot comply solely by using a low-carbon but energy-intensive fuel (NCM Modelling Guide, Section 7.2).

Why the grid electricity factor has fallen

The 42% reduction in the grid electricity CO₂ factor reflects the rapid growth of renewable generation in the UK electricity mix since the Part L 2021 factors were set. Wind, solar, and nuclear now account for a much larger share of generation, displacing coal and gas. The factor represents the average carbon intensity of grid electricity over a projected year, taking into account the expected generation mix at the time the regulation takes effect.

Fossil fuel emission factors (gas, oil, LPG, coal) are inherent properties of the fuel's chemical composition and combustion process – they do not change with grid decarbonisation. This creates a widening gap between electricity-based and fossil-fuel-based heating, which is the central policy lever of the Future Buildings Standard.

Why electric heating is now more favourable

The updated factors transform the economics of the Part L calculation for heating systems. Consider the effective emission factor per kWh of delivered heat for different systems (NCM Modelling Guide, Section 7.3):

An ASHP with a seasonal CoP of 3.0 produces just 0.045 kgCO₂ per kWh of heat – roughly one-fifth of a gas boiler at 0.221 kgCO₂. Even direct electric resistance heating at 0.136 kgCO₂ is substantially lower than gas. This arithmetic is the reason the FBS effectively mandates heat pumps for new non-domestic buildings.

Impact on SBEM compliance outcomes

The updated factors affect compliance in several interconnected ways:

• Heat pump buildings benefit significantly. The lower electricity factor means heat pump systems produce far lower calculated emissions than under Part L 2021, making the BER easier to meet.
• Gas buildings are heavily penalised. Gas emission factors are unchanged, but the notional building now assumes a heat pump. The TER is set by a low-carbon notional building, and a gas-heated actual building must compete against this target – which it almost certainly cannot meet.
• Solar PV value increases. Each kWh of PV generation offsets grid electricity at 0.136 kgCO₂/kWh. While the absolute CO₂ offset per kWh is lower than under the 2021 factors, PV remains essential for meeting the tighter targets set by the low-carbon notional building.
• The dual metric prevents shortcuts. A building that passes on CO₂ (BER ≤ TER) must also pass on primary energy (BPER ≤ TPER). Electricity's high primary energy factor (1.501 kWh_PE/kWh) means that electric systems need to be efficient – direct electric heating passes on carbon but may struggle on primary energy.

District heating treatment

District heating receives special treatment in the 2026 NCM. Rather than a fixed emission factor, the factors depend on the declared carbon intensity and primary energy intensity of the specific heat network. This allows well-performing networks (especially those using waste heat, heat pumps, or renewable sources) to demonstrate good compliance outcomes (NCM Modelling Guide, Section 7.1).

The 2026 iSBEM includes standardised inputs for heat network connections, with a compliance route based on the network's declared performance data. Buildings connected to district heating are also exempt from the fossil fuel restrictions in AD L2 2026, paragraph 4.4, reflecting the policy position that heat networks are a viable low-carbon heating route even where the current heat source may be partially fossil-fuelled.

Biomass factors

Biomass fuels (wood pellets at 0.039 kgCO₂/kWh and wood chips at 0.019 kgCO₂/kWh) have very low emission factors, reflecting that the CO₂ released during combustion is offset by CO₂ absorbed during growth. However, biomass heating in non-domestic buildings is constrained by practical factors:

• Air quality regulations – particulate emissions from biomass combustion are subject to increasingly strict controls, especially in urban areas
• Fuel storage and delivery requirements – biomass systems need substantial on-site storage and regular deliveries
• Maintenance intensity – biomass boilers require more frequent servicing than gas or heat pump systems

Where biomass is used, its low CO₂ factor gives a strong compliance advantage on the emissions metric. The primary energy factor for wood pellets (1.325 kWh_PE/kWh) is higher than for gas (1.126), which partially offsets the CO₂ benefit when assessed against the BPER/TPER target.