Heat pumps and air conditioning
Domestic heat pumps include wet heating systems, ground-source equipment and fixed air-to-air systems sold as air conditioning. The survey and design work depends on whether the equipment is providing space heating, cooling, hot water or a combination of these duties.
Current UK research
DESNZ published detailed modelling of reversible air-to-air heat pumps in UK homes in July 2026.
Read the DESNZ publication →Domestic system types
Air-source systems can feed a wet heating circuit or deliver conditioned air directly to rooms. Ground and water source systems use a different source arrangement. Each type has its own indoor equipment, calculations and hot-water requirements.
Air-to-water heat pumps
An outdoor unit supplies a wet heating system and normally a hot-water cylinder. Heat loss, water temperatures, emitters and hydraulic design determine the installation.
Reference entry →Fixed air conditioning
A reversible air-to-air system heats and cools through indoor fan units. It does not normally provide domestic hot water or supply a wet radiator circuit.
Reference entry →Ground and water source
Ground loops, boreholes or a suitable water source collect heat for a heat pump. Source access, permissions and circulating equipment become part of the project.
Reference entry →Fixed air conditioning and mini-splits
Domestic fixed AC uses a reversible refrigerant circuit, with an outdoor unit connected to one or more indoor units. It can cool in summer and provide air-to-air heating when the equipment and design cover that duty.
The matched indoor and outdoor models, room duties, pipe routes, condensate drainage, electrical requirements, controls and service access define the installed system. Domestic hot water normally remains separate, although some compatible air-to-air platforms can connect dedicated hot-water equipment.
Air-to-air heat-pump reference →Portable AC sits outside the equipment catalogue
A portable room unit contains its working equipment in the appliance and rejects heat through an exhaust hose. Energy Stack explains the category, but the manufacturer and model catalogue covers fixed residential systems rather than portable appliances.
Portable air conditioners →Fixed AC system design
Rooms and loads
Cooling load and heating loss are separate calculations. Glazing, orientation, solar gain, room volume, occupancy, insulation and ventilation can all affect selection.
Read the reference →Single-split or multi-split
One outdoor unit can serve one indoor unit or, on a compatible multi-split system, several. Permitted combinations and available output come from the manufacturer’s selection data.
Read the reference →Indoor-unit format
High-wall, floor-console, cassette and concealed ducted units place different demands on the room, ceiling void, airflow route, drainage and service access.
Read the reference →Condensate
Cooling produces water at the indoor unit. It needs a gravity drain or condensate-pump arrangement and a suitable discharge point.
Read the reference →Air-to-air room coverage
Air-to-air heating and cooling can cover one room, several rooms or a whole home. The equipment arrangement and air distribution differ between these systems.
Single-room systems
A single-split connects one indoor unit to one outdoor unit. The indoor unit can be high-wall, floor-mounted, cassette or concealed ducted equipment.
Multi-room and whole-home systems
A multi-split connects several permitted indoor units to one outdoor unit. Whole-home layouts can also use more than one single-split system or combine single-split and multi-split equipment.
Concealed ducted systems
One concealed indoor unit can distribute air to several rooms through ducts and grilles. The design includes supply and return air paths, duct space, sound, drainage and service access.
Fixed monobloc systems
A fixed monobloc or through-wall unit keeps the refrigerant circuit in one casing and uses openings through an outside wall. It is a fixed system rather than a portable room appliance.
Air-to-water heat-pump design
A wet heat-pump system is designed around the building heat loss, water temperatures and the equipment that transfers heat into each room and the hot-water cylinder.
Room-by-room heat loss
The calculation records room dimensions, fabric, ventilation and design temperatures. It establishes the heat needed in each room and for the home.
Read the reference →Water temperature and emitters
Radiator and underfloor-heating output must be checked at the proposed flow and return temperatures. Existing radiators can remain where the calculation supports them.
Read the reference →Pipework and flow
Flow rate, pressure loss, pipe sizes, pump duty and system volume affect heat transfer and cycling. The complete hydraulic arrangement needs to be shown.
Read the reference →Hot water and controls
Cylinder volume, coil performance, reheat time, hot-water priority, weather compensation and backup settings are part of the system design.
Read the reference →Siting, planning and installation routes
Outdoor units need project-specific airflow, sound, drainage and service checks. Planning rules differ across the UK. In England, the current permitted-development route for a domestic ASHP (air source heat pump) includes conditions on siting, MCS 020 a compliance and use: a unit used solely for cooling does not meet that route.
Split systems also involve refrigerant pipework. In Great Britain, work on stationary equipment containing F gas requires the appropriate qualification for the activity.
Planning and outdoor-unit siting →- Airflow clearances and service access around each outdoor unit
- Sound data and the relevant neighbouring assessment position
- Planning rules for the property, location, intended use and UK nation
- Electrical supply, circuit protection, isolation and any DNO process
- Refrigerant pipework, water pipework, cable routes and wall penetrations
- Indoor cooling condensate and outdoor heating or defrost water
Other residential heat-pump arrangements
The main categories do not cover every domestic system. Cooling through a wet circuit, ventilation heat recovery and hot-water-only equipment have different system boundaries.
Reversible air-to-water cooling
Some air-to-water heat pumps can also supply chilled water. Cooling needs compatible emitters such as fan coils, together with suitable controls, water temperatures and condensate drainage.
Exhaust-air heat pumps
An exhaust-air heat pump recovers energy from extract ventilation air. Domestic products can combine ventilation, space heating and hot water without a conventional outdoor unit.
Domestic hot-water heat pumps
A domestic hot-water heat pump heats stored water. Space heating remains a separate system.
Air conditioning references
Heat-pump and air-conditioning guides
Air-to-water and air-to-air systems have different design, installation and operating requirements. The guides cover those subjects separately, including fixed and portable cooling.
Home air conditioning in the UK
Fixed air-to-air systems, single-split and multi-split layouts, indoor-unit types, room coverage, sizing and efficiency ratings.
Read the guide →Installing fixed air conditioning
Room loads, indoor and outdoor unit siting, planning, F-gas work, electrical supply, condensate, commissioning and records.
Read the guide →Running home air conditioning efficiently
Heat-gain control, set points, schedules, airflow, filters, electricity monitoring and operation with solar PV.
Read the guide →Portable versus fixed air conditioning
Heat rejection, room coverage, efficiency information, installation and condensate for portable and fixed systems.
Read the guide →Home air-source heat-pump installation
The survey, heat-loss work, hydraulic design, installation, commissioning and handover for an air-to-water system.
Read the guide →Comparing air-source heat-pump quotes
The design records, equipment, emitters, hot water, electrical work, controls and exclusions that allow two proposals to be compared.
Read the guide →Heat-pump controls and settings
Weather compensation, schedules, setbacks, hot-water cycles, backup heat and the settings recorded at handover.
Read the guide →Current official information
Checked 28 July 2026. The live sources carry current standards, research, planning conditions and qualification rules.