Heat Pump Requirements and Low-Carbon Heating

What This Requirement Covers

The 2021 edition of Approved Document L and the forthcoming Future Homes Standard strongly favour low-carbon heating systems, particularly heat pumps, as the primary means of compliance with carbon emission targets. While Part L does not mandate a specific heating technology, the carbon emission targets are set at levels that make heat pumps the most straightforward compliance route for new dwellings.

Key Requirements

Heat Pump Types

1. Air source heat pumps (ASHP): Extract heat from outside air; the most common type in UK domestic installations. Available as monobloc (outdoor unit only) or split (outdoor and indoor units)
2. Ground source heat pumps (GSHP): Extract heat from the ground via buried loops or boreholes; higher efficiency but significantly higher installation cost
3. Water source heat pumps: Extract heat from a body of water; suitable only for specific sites
4. Hybrid heat pumps: Combine a heat pump with a gas boiler; the heat pump handles most heating, with the boiler providing supplementary heat in very cold conditions

Performance Standards

1. Heat pumps must have a Seasonal Coefficient of Performance (SCOP) of at least 2.5 for space heating (i.e., for every 1 kW of electricity consumed, at least 2.5 kW of heat is produced)
2. In practice, air source heat pumps typically achieve SCOP of 2.8-3.5, and ground source heat pumps achieve 3.5-4.5
3. Heat pumps must be MCS certified (Microgeneration Certification Scheme) to qualify for the Boiler Upgrade Scheme grant
4. Installation must be carried out by an MCS-certified installer

Radiator and Emitter Design

1. Heat pumps operate most efficiently at lower flow temperatures (35-45 degrees C) compared to gas boilers (60-80 degrees C)
2. Radiators in heat pump systems must be larger than those used with gas boilers to compensate for the lower flow temperature
3. Underfloor heating is highly compatible with heat pumps due to its large surface area and low flow temperature requirement
4. Fan-assisted radiators can also be used to achieve higher output at lower flow temperatures

Noise and Planning

1. Air source heat pumps produce noise from the compressor and fan; this must comply with MCS 020 (Planning Standards)
2. Permitted development rights allow ASHP installation without planning permission in most cases, subject to:

- Maximum volume of the outdoor unit: 0.6 m³ - Minimum distance from the property boundary: 1 metre - Noise level: Must not exceed 42 dBA at the nearest neighbour's window (measured 1 metre from the window)

1. Planning permission is required in conservation areas, on listed buildings, and where permitted development rights have been removed

The Boiler Upgrade Scheme

1. The Government's Boiler Upgrade Scheme provides grants of up to GBP 7,500 for air source heat pumps and GBP 7,500 for ground source heat pumps (as of 2024)
2. The property must have a valid EPC (no older than 10 years)
3. The heat pump must be installed by an MCS-certified installer
4. The scheme runs until March 2028

Practical Compliance Tips

1. Design the heating system for low flow temperatures from the outset; retrofit heat pump installations in older properties may require radiator upgrades
2. Carry out a heat loss calculation for each room to size radiators correctly for the lower flow temperature
3. Specify a hot water cylinder with a heat pump coil; heat pumps cannot produce instant hot water like a combi boiler
4. Check the electrical supply capacity; a typical 8-12 kW ASHP may require a dedicated electrical circuit and possibly a supply upgrade
5. Position the outdoor unit away from bedroom windows (the homeowner's and the neighbour's) and in a well-ventilated location
6. Consider the defrost cycle noise; ASHPs defrost periodically in cold weather, producing additional noise
7. Keep the MCS certificate and commissioning data for the EPC assessment and building control sign-off