Non-Domestic Heating Requirements Under the FBS

The Future Buildings Standard introduces low-carbon heating as the default for new non-domestic buildings. Through fuel emission and primary energy factor caps, AD L2 2026 effectively rules out fossil fuel heating in new buildings, making heat pumps or district heat networks the standard choice. This page covers the fuel restrictions, heat pump requirements, flow temperature limits, and controls guidance from the 2026 edition (AD L2 2026, Section 4).

Fuel restrictions for new buildings

For heating and hot water systems in new non-domestic buildings, the fuel must meet both of the following thresholds (AD L2 2026, para 4.4):

• CO₂ emission factor of no greater than 0.086 kgCO₂/kWh (as listed in the NCM Modelling Guide)
• Primary energy factor of no greater than 1.969 kWhPE/kWh (as listed in the NCM Modelling Guide)

Alternatively, the heating may be provided by a district heat network.

A limited exception exists for backup heating and hot water systems: they need not meet the fuel restrictions where there is no suitable low-carbon alternative and failure would present a significant life safety risk or risk to critical national infrastructure (AD L2 2026, para 4.4).

Low-carbon heating in the notional building

The notional building assumes a low-carbon heating system such as an air-source heat pump with a suitable coefficient of performance (COP). Because the TER and TPER are derived from this notional building, specifying fossil fuel heating in the actual building creates a large deficit that is extremely difficult to overcome through other measures (AD L2 2026).

Side-lit vs top-lit buildings

The notional building specification distinguishes between building types based on their lighting arrangement, which also affects the assumed heating system:

• Side-lit buildings (offices, schools, retail) – the notional building assumes heat pumps as the primary heating system, reflecting the suitability of wet distribution systems (radiators, underfloor heating) in these building types
• Top-lit buildings (warehouses, industrial units, large retail sheds) – the notional building assumes radiant electric heating, reflecting the practical challenges of heating large-volume spaces with wet systems and the effectiveness of radiant heating in such environments

This distinction is important because it affects the TER and TPER targets. A warehouse specifying heat pumps where the notional building assumes radiant heating will have different compliance dynamics than an office, and vice versa. Understanding the notional building's assumptions for your building type is essential for an effective design strategy.

Heat pump requirements

Coefficient of performance (COP)

Heat pumps are the primary low-carbon heating technology for most new non-domestic buildings. AD L2 2026 requires heat pumps between 400 kW and 1000 kW output (other than air-to-air), and heat pumps used for domestic hot water heating only, to have a COP of 2.5 or higher (AD L2 2026, Section 5).

For heat pumps up to 400 kW, Ecodesign product regulations set minimum efficiency standards. Table 5.1 of AD L2 2026 maps heat pump types to the applicable EU Ecodesign regulation, covering air-to-water, ground-source, water-source, and air-to-air configurations at various output ranges.

Heat pump types

The choice of heat pump technology depends on the building type, available external space, and heating distribution design:

• Air-source heat pumps (ASHP) – the most common choice for commercial buildings. Require external condensing units with adequate ventilation. Controls must protect against air flow failure and manage defrost cycles (AD L2 2026, Table 5.2)
• Ground-source heat pumps (GSHP) – suitable where ground conditions and available land permit borehole or trench installation. Controls must protect against water flow failure and manage both internal and external water pumps (AD L2 2026, Table 5.2)
• Water-source heat pumps – used where a suitable water source is available (rivers, aquifers, lakes). Similar control requirements to ground-source systems
• Air-to-air heat pumps – providing direct warm air heating. Covered by different Ecodesign regulations depending on output (above or below 12 kW). Must include defrost control and secondary heating control (AD L2 2026, Table 5.2)

Flow temperature – 55°C maximum

New wet heating systems (newly installed or fully replaced) must be sized for a maximum flow temperature of 55°C. The guidance states that it is preferable to design to a lower flow temperature than 55°C to maximise heat pump efficiency (AD L2 2026, para 4.12).

In existing buildings where 55°C is not technically feasible – for example, where existing radiators are undersized for lower temperatures – the system should be designed to the lowest temperature that meets heating needs (AD L2 2026, para 4.12).

Hot water systems

Domestic hot water (DHW) systems in new non-domestic buildings are subject to the same fuel restrictions as heating systems. Minimum thermal efficiencies for DHW systems are set out in Table 5.6 of AD L2 2026, with natural gas direct-fired systems requiring 91% gross calorific value efficiency and electrically-heated systems assumed at 100% (AD L2 2026, Table 5.6).

The backup system exception also applies to hot water – fossil fuel backup DHW systems are permitted only where no suitable low-carbon alternative exists and failure would present a life safety risk or risk to critical national infrastructure.

Controls and zoning

The FBS places significant emphasis on heating controls to prevent energy waste. Key requirements include (AD L2 2026, paras 4.13–4.16):

• Zoning: systems must be subdivided into separate control zones for areas with significantly different solar exposure, pattern of use, or type of use
• Independent control: each zone must have independent timing and temperature control
• Heating/cooling interlock: where both heating and cooling are provided, controls must prevent simultaneous operation in the same space
• Central plant default: central plant should operate only when zone systems require it, with the default condition set to off
• Weather compensation: required where appropriate and technically feasible
• Thermostatic room controls: each room should have thermostatic controls in new buildings or when a heat generator is replaced (with limited exceptions for rooms with very low heat demand below 10 W/m²)

System sizing

Heating systems must be sized based on a heat loss calculation per BS EN 12831-1 and CIBSE Guide B1. Systems should not be significantly oversized – oversizing wastes energy through short cycling and reduces heat pump efficiency. Accurate heat loss calculations are essential for right-sizing the system (AD L2 2026, para 4.11).

System treatment and commissioning

Before a new heating appliance is installed, all central heating and primary hot water circuits must be cleaned and flushed. A suitable chemical inhibitor should be added to the primary heating circuit. In hard water areas (greater than 200 ppm CaCO₃), feed water to water heaters and hot water circuits must be treated to reduce limescale (AD L2 2026, para 4.15).

All fixed building services – including heating – must be commissioned to ensure they use no more fuel and power than is reasonable. A commissioning plan identifying systems, tests, schedules, and responsibilities must be provided to the building control body before work begins. The BRUKL report documents both the design-stage and as-built heating specifications (AD L2 2026, Section 7).

Impact of specifying gas boilers

While the fuel restrictions technically apply only to new buildings, understanding their impact is critical for project planning. A new non-domestic building specifying a gas boiler will face:

• Immediate non-compliance with the fuel emission and primary energy factor caps (para 4.4)
• A large deficit against the TER and TPER, because the notional building assumes low-carbon heating
• The need to compensate through dramatically improved fabric, extensive solar PV, and other measures – making compliance impractical in most cases

The government's consultation response confirmed that the intention is to phase out fossil fuel heating in new non-domestic buildings, aligning with the net zero 2050 target. The FBS achieves this through the combined effect of fuel restrictions and the low-carbon notional building specification.

Building automation and control systems

New buildings with heating or air-conditioning systems with an effective rated output greater than 180 kW must install a building automation and control system (BACS). The BACS must comply with BS EN ISO 16484 and continuously monitor, log, and analyse energy use. A BS EN ISO 52120-1 Class A rated system meets these requirements (AD L2 2026, paras 5.76–5.84).