Glossary

Key Terms & Definitions

A comprehensive reference for the terminology used in the Future Homes Standard, building regulations, and low-carbon heating systems.

Air Source Heat Pump(ASHP): A heating system that extracts heat from ambient outdoor air and transfers it to indoor spaces via a refrigerant cycle. The most common low-carbon heating solution for FHS-compliant homes, achieving COPs of 3.0–4.0 at design conditions.
Airtightness: A measure of how well a building prevents uncontrolled air leakage through the building envelope. Measured in m³/h/m² at 50 Pascals pressure. FHS requires 3 m³/h/m² at 50Pa — approximately three times tighter than Part L 2021.
BREL Report(BREL): Building Regulations England Part L report — produced by approved energy modelling software, providing building control bodies with compliance information in a standardised format. Under the FHS, voluntary delivered energy reporting is also available via the BREL where the Home Energy Model is used.
Building Regulations: The statutory instruments that set standards for the design and construction of buildings in England and Wales. The Future Homes Standard amends Part L (conservation of fuel and power) and introduces requirements under Part F (ventilation) and Part O (overheating).
Building Safety Regulator(BSR): The body responsible for overseeing the safety and standards of Higher-Risk Buildings in England, established under the Building Safety Act 2022. The BSR manages the Gateway process for HRBs and is considering what can be done to address common issues highlighted in the Part O call for evidence.
Coefficient of Performance(COP): The ratio of heat output to electrical input for a heat pump. A COP of 3.0 means the heat pump produces 3kW of heat for every 1kW of electricity consumed. Higher COPs indicate greater efficiency. COP varies with flow temperature — lower flow temperatures yield higher COPs.
Commissioning: The process of testing, adjusting, and verifying that building services systems (heating, ventilation, hot water) are installed correctly and operating at their design performance. FHS requires commissioning certificates for MVHR and heating systems.
Competent Person Scheme: A certification scheme that allows registered installers to self-certify that their work complies with building regulations without the need for building control inspection. Under the FHS, competent person schemes are recommended for heat pump and mechanical ventilation installations. Registered schemes for heat pumps include APHC, BESCA, Certsure, HETAS, NAPIT, and OFTEC.
Decentralised Mechanical Extract Ventilation(dMEV): A ventilation system using individual extract fans in wet rooms (kitchens, bathrooms) to remove moist air. Included in the FHS notional building specification. Under the updated Approved Document F, there is no longer an explicit maximum duct length for dMEV, but design verification by a competent person is required for duct lengths over 2 metres.
Delta-T(ΔT): The temperature difference between the heating system water and the room air, used to calculate emitter heat output. At lower flow temperatures (heat pump operation), delta-T is smaller, meaning each emitter produces less heat — requiring larger or more emitters.
District Heating: A system where heat is generated centrally and distributed to multiple buildings through a network of insulated pipes. Also known as heat networks. Can achieve FHS compliance when supplied by low-carbon heat sources.
Dwelling Emission Rate(DER): The calculated CO₂ emissions per square metre of floor area per year for a dwelling, based on standardised assumptions about occupancy and use. Under FHS, the DER must be 75–80% lower than the 2013 baseline Target Emission Rate.
Energy Performance Certificate(EPC): A certificate rating the energy efficiency of a building on a scale from A (most efficient) to G (least efficient). FHS homes are expected to achieve EPC ratings of A or high B.
Fabric Energy Efficiency(FEE): A metric measuring the energy demand of a building's fabric (walls, roof, floor, windows) independent of the heating system or renewable generation. FEE is one of three performance metrics used for FHS compliance alongside Target Emission Rate (TER) and Target Primary Energy Rate (TPER). The government has confirmed these metrics will be retained for the FHS.
Fabric First: A design approach that prioritises the thermal performance of the building envelope (walls, roof, floor, windows) before considering heating system efficiency. FHS strongly supports this approach with its demanding U-value and airtightness targets.
Fan Convector: A heat emitter that uses an integrated fan to force air across a heat exchanger, increasing output from a compact unit. Offers the fastest response time of any emitter type but produces audible noise (25–35dB). Operates well at low flow temperatures.
Flow Temperature: The temperature of water leaving the heat pump and entering the heating distribution circuit. Lower flow temperatures increase heat pump COP. FHS-optimised systems typically operate at 35–45°C, compared to 65–80°C for gas boiler systems.
Future Homes Standard(FHS): A 2025 UK building regulation requiring new homes in England to produce 75–80% less carbon than 2013 baseline homes. Mandates low-carbon heating, high insulation standards, triple glazing, and MVHR. Replaces SAP with the Home Energy Model.
Gateway 2(GW2): A regulatory approval stage in the Building Safety Act 2022 process for Higher-Risk Buildings. Developers must submit detailed plans to the Building Safety Regulator for approval before construction can begin. Under FHS transitional arrangements, a valid GW2 application must be submitted before 24 September 2027 for HRB work to benefit from transitional provisions.
Ground Source Heat Pump(GSHP): A heating system that extracts heat from the ground via buried pipework (horizontal trenches or vertical boreholes). Achieves higher COPs than ASHPs (typically 4.0–5.0) due to stable ground temperatures, but with higher installation costs.
Heat Loss Calculation: A room-by-room calculation of the rate at which a building loses heat through its fabric and ventilation. Essential for sizing heating systems and emitters correctly. Must use actual FHS fabric performance values, not generic assumptions.
Heat Network: See District Heating. A centralised heat distribution system serving multiple buildings from a shared heat source.
Heat Network Zoning: A regulatory framework being developed under the Energy Act 2023 to designate areas where heat networks are expected to be the lowest-cost solution for decarbonising heat. Buildings in designated zones may be required to connect to a heat network. The FHBS Approved Documents will be kept under review to align with heat network zoning regulations as they develop.
Higher-Risk Building(HRB): A building at least 18 metres in height or 7 storeys that contains at least 2 residential units, or is a care home or hospital. HRBs must pass through a Gateway process managed by the Building Safety Regulator before construction and occupation. They have separate transitional arrangements under the FHBS, with regulations coming into force on 24 September 2027.
Home Energy Model(HEM): The replacement for SAP as the energy assessment methodology under FHS. A more sophisticated whole-building model that accounts for thermal mass, realistic occupancy, actual heating system performance, and interactions between building systems. Available from 2026.
Home User Guide: A document provided to new homeowners containing information on how to operate and maintain their home's ventilation, heating, hot water, on-site electricity generation, and overheating systems. Under the FHS, Regulation 40C requires this to be provided in an appropriate format — both paper and digital copies should be given, or a paper copy with a digital copy made available.
Hybrid Heat Pump: A system combining a heat pump with a gas or oil boiler. The heat pump operates at lower outdoor temperatures and the boiler supplements during peak demand. May achieve FHS compliance in limited circumstances but is not the primary compliance route.
Linear Thermal Transmittance(Ψ (psi)): A measure of heat loss at junctions between building elements (e.g., wall-to-floor, wall-to-roof). Also called thermal bridging. FHS requires careful detailing to minimise Ψ-values at all junctions.
Material Change of Use(MCU): A conversion of a building from one purpose to another, such as converting an office into flats. MCU dwellings are currently subject to lower minimum standards than new-build dwellings. The government has retained current MCU standards under the FHS but plans further consultation on uplifted requirements.
MCS Certification: Microgeneration Certification Scheme — the quality assurance standard for renewable energy installations in the UK. Heat pump installations must be carried out by MCS-certified installers to qualify for FHS compliance and government incentive schemes.
Mean Water Temperature(MWT): The average of the flow and return water temperatures in a heating circuit. Emitter output is determined by the difference between MWT and room temperature. Lower MWT means lower emitter output per unit, requiring larger emitters.
Mechanical Ventilation with Heat Recovery(MVHR): A ventilation system that extracts stale air from wet rooms and supplies fresh air to living spaces, recovering 85–95% of the heat from the extract air via a heat exchanger. Essential in airtight FHS homes to maintain indoor air quality.
Minimum Energy Efficiency Standards(MEES): Regulations requiring rented properties to meet a minimum EPC rating. Currently EPC E, with proposals to raise to EPC C. Applies to existing buildings, not new builds — but demonstrates the direction of travel in building energy policy.
Notional Building: A reference building specification used to set tailored performance targets for new dwellings and non-domestic buildings. The actual building must achieve the same or better level of energy and carbon performance as the notional building. The FHS notional building includes a heat pump, solar PV, wastewater heat recovery, and enhanced fabric standards.
Overheating: The risk of excessive indoor temperatures, particularly in summer. Highly insulated, airtight FHS homes are more susceptible to overheating. Part O of the Building Regulations and TM59 methodology address this risk through design requirements.
Part F: The section of the Building Regulations covering ventilation. Works in conjunction with FHS to ensure adequate indoor air quality in highly airtight homes. Specifies minimum extract and whole-dwelling ventilation rates.
Part L: The section of the Building Regulations covering conservation of fuel and power. The Future Homes Standard is implemented as an amendment to Part L, significantly tightening the carbon emission and fabric performance requirements for new homes.
Part O: The section of the Building Regulations covering overheating, introduced in 2022. Requires new homes to be designed to limit the risk of excessive indoor temperatures, using TM59 assessment methodology.
Passive Cooling: Design strategies that reduce overheating risk without mechanical cooling — including external shading, cross-ventilation, appropriate glazing ratios, low g-value glass, thermal mass, and MVHR summer bypass modes.
Primary Energy: The total energy consumed including generation and transmission losses. FHS assesses primary energy use to account for the full carbon impact of electricity and other fuels, not just the energy consumed at the meter.
Return Temperature: The temperature of water returning to the heat pump after circulating through the heating system. The difference between flow and return temperatures indicates how much heat the emitters have extracted from the water.
SAP(SAP): Standard Assessment Procedure — the current methodology for assessing the energy performance of dwellings, being replaced by the Home Energy Model (HEM) under FHS. SAP has been criticised for using simplified assumptions that do not reflect real-world performance.
SAP 10.3(SAP 10.3): An updated version of the Standard Assessment Procedure made available for FHS compliance. SAP 10.3 is the approved calculation methodology at FHS launch, with the Home Energy Model (HEM) to follow during a dual running period of at least 24 months. Either methodology can be used to demonstrate compliance during dual running.
Seasonal COP(SCOP): The average coefficient of performance of a heat pump over an entire heating season, accounting for varying outdoor temperatures. A more realistic measure of heat pump efficiency than instantaneous COP. FHS homes should target SCOP of 3.0+.
Skirting Board Heating: A low-profile heat emitter system that replaces conventional skirting boards with hydronic heat exchangers running along the perimeter of rooms. Operates at 35–50°C flow temperatures, making it well-suited to heat pump systems. The extended linear length provides substantial surface area for heat emission at low flow temperatures. Products such as ThermaSkirt (www.discreteheat.com) are examples of this technology, offering a discreet whole-house heating solution that replaces standard skirting boards.
Smart Meter: A digital energy meter that automatically sends readings to the energy supplier and provides real-time usage data to the consumer. Updated voluntary guidance for smart meter installation in new buildings has been published alongside the FHS, covering both domestic and non-domestic properties. The guidance addresses connectivity, placement, and signal propagation issues.
Solar Gain: Heat gained from sunlight entering through windows. Beneficial in winter (reducing heating demand) but a major overheating risk factor in summer. FHS design must balance solar gain through appropriate glazing ratios and shading strategies.
Specific Fan Power(SFP): A measure of the energy efficiency of a ventilation fan system, expressed as watts per litre per second (W/l/s). Lower SFP indicates a more efficient fan. The FHS has revised the maximum SFP for continuous dMEV systems to 3.5 W/l/s, following consultation feedback that the originally proposed level was too challenging to achieve.
Target Emission Rate(TER): The maximum CO₂ emission rate allowed for a dwelling under building regulations. The TER is calculated based on a notional building of the same size and shape. FHS homes must achieve a Dwelling Emission Rate (DER) 75–80% below the 2013 TER.
Target Primary Energy Rate(TPER): A performance metric measuring the total primary energy consumption of a building, including generation and transmission losses. TPER is used alongside TER and FEE to assess FHS compliance. The government has confirmed these three metrics will continue to be used for setting performance requirements under the FHS.
Thermal Bridge: A localised area of the building envelope with significantly higher heat transfer than the surrounding area — typically at junctions, around windows, or where structural elements penetrate insulation. Careful detailing is essential for FHS compliance.
Thermal Mass: The ability of building materials to absorb, store, and release heat. High thermal mass (e.g., concrete, masonry) can moderate indoor temperature swings, reducing both overheating risk and heating demand peaks. HEM accounts for thermal mass more accurately than SAP.
TM59: CIBSE Technical Memorandum 59 — the methodology for assessing overheating risk in dwellings. Living rooms must not exceed 28°C for more than 3% of occupied hours; bedrooms must not exceed 26°C for more than 1% of occupied hours.
Triple Glazing: Windows with three panes of glass separated by two insulating gas-filled cavities. Required under FHS to achieve the window U-value of 1.2 W/m²K. Also improves acoustic performance compared to double glazing.
U-Value: A measure of how quickly heat passes through a building element, in watts per square metre per degree Kelvin (W/m²K). Lower U-values indicate better insulation. FHS requires walls 0.18, roof 0.13, floor 0.13, windows 1.2 W/m²K.
Underfloor Heating(UFH): A heating system where warm water circulates through pipes embedded in the floor. Operates at the lowest flow temperatures of any emitter type (35–45°C), maximising heat pump COP. Response time is slow (1–6 hours) due to thermal mass of the floor. Heat pumps are typically run continuously to mitigate response time issues.
Ventilation Heat Loss: Heat lost through the movement of air into and out of a building — both controlled ventilation (e.g., MVHR) and uncontrolled air leakage. FHS minimises uncontrolled losses through airtightness and recovers heat from controlled ventilation via MVHR.
Wastewater Heat Recovery(WWHR): A system that captures heat from wastewater (typically from showers) and uses it to pre-heat incoming cold water. Included in the FHS Option 1 notional building specification for multi-storey dwellings, reducing hot water energy demand and improving overall building performance.
Weather Compensation: A control strategy where the heat pump modulates its flow temperature based on outdoor temperature. Warmer outside temperatures allow lower flow temperatures, improving COP. Essential for optimising heat pump performance in FHS homes year-round.
Whole-House Design: An integrated approach to building design that considers fabric, heating, ventilation, and renewables as an interconnected system rather than isolated components. Central to the HEM methodology and FHS compliance philosophy.
Zero Carbon Ready: A home designed and built so that it can become fully zero carbon as the electricity grid decarbonises, without requiring further physical retrofit. FHS homes are intended to be zero carbon ready — their carbon emissions reduce automatically as grid electricity becomes cleaner.