Size the heat pump, match the cylinder, and order every fitting in one basket. This guide explains how an air source heat pump system is put together, and the kit builder below turns your home’s details into a full parts list from Panasonic, Grant, Mitsubishi Electric, Samsung and the other brands we stock.
Supply only, with live prices and stock. Installers: every kit can earn you commission through the AIZO Partner Program.
Build your heat pump kit
Work down the four steps. The parts list updates as you go, and the drawing shows which parts of the system your kit covers. Untick anything you already have.
How much heat does your home need?
Use the whole-house figure from your MCS heat loss survey at the design outdoor temperature for your area.
An estimate using the simplified EN 12831 approach behind our heat pump sizing calculator. An installer’s room-by-room heat loss survey must confirm the size before you buy.
Choose your heat pump
Our four main brands are listed first. Each unit shows its smallest output that meets your design load, so nothing is undersized.
Hot water cylinder
Cylinders made for or matched to your heat pump brand are listed first, and only compatible ones are shown. Brand-locked cylinders, such as Ecodan FTC7 and Samsung ClimateHub, appear only with their own brand.
How will the system be installed?
Estimated system volume: —. Used to size the expansion vessel, glycol and water treatment.
Your parts list
Each line says why it is there. Untick what you don’t need, change quantities, then add the whole kit to your basket.
How a heat pump system fits together
A monobloc air source heat pump holds the whole refrigerant circuit inside the outdoor unit. Indoors, it connects to your heating like a boiler would: a flow pipe carries warm water in, a return pipe brings cooler water back. The parts in between protect the heat pump, keep the water clean and the pressure stable, and send heat to either the radiators or the cylinder.
Anti-vibration feet
Lift the unit clear of snow, leaves and standing water so the evaporator can drain during defrost. Rubber mounts stop compressor vibration reaching walls and floors.
Flexible hoses
Short insulated braided hoses join the unit to rigid pipework. They absorb vibration and allow for small movements between the unit and the house.
Isolation valves
One on the flow and one on the return, close to the unit. Closing them lets an engineer work on the heat pump without draining the house. A valve with a built-in strainer on the return adds a second line of defence against debris.
Magnetic filter
The plate heat exchanger inside a heat pump has very fine channels. A heat-pump-rated filter on the return, such as the IntaKlean HP, catches magnetite sludge and loose debris before it gets there. Fit it where it is easy to clean at every service.
Fill and flush valve
A dedicated point on the primary pipework for filling, flushing and draining. Flush the system through a bypass or a temporary loop rather than through the heat pump, so debris from old pipework never reaches it.
Expansion vessel
Water expands as it heats. A pressurised vessel takes up that expansion so system pressure stays within limits. Size it to roughly a tenth of total system volume, or as the manufacturer specifies.
Primary pump
Some monobloc units have a pump built in. Others, such as Samsung standard monoblocs and Ecodan outdoor units used with non-Ecodan cylinders, need an external pump. A speed-controlled pump driven by the heat pump’s own signal keeps the flow rate right as conditions change.
Buffer, volumiser or low loss header
A heat pump needs enough water in circulation to defrost and to run long, steady cycles. A volumiser adds volume in series. A low loss header or four-port buffer separates the heat pump circuit from a heavily zoned heating circuit, which then needs its own secondary pump.
Automatic bypass
On a direct system, TRVs and zone valves can close until almost no water flows, which trips the heat pump on low flow. An automatic bypass valve opens as pressure rises to keep a minimum flow. It isn’t needed if one circuit is left permanently open.
Diverter or zone valves
A motorised three-port diverter, such as the Honeywell V4044C, sends the heat pump’s output either to the heating or to the cylinder. Don’t use a mid-position valve (V4073A): it can open to both circuits at once. An S-plan with two Honeywell 2-port valves also works if the controller has outputs for both. Pre-plumbed cylinders usually include the valve, already wired.
Heat pump cylinder
Heat pumps heat water to around 50–55°C, not the 60–70°C a boiler reaches. A heat pump cylinder has a much larger coil, often around 3m², so it can take heat quickly at those lower temperatures. A standard boiler cylinder’s coil is far too small, even if it is labelled indirect.
Controller and room thermostats
The heat pump’s own controller runs weather compensation, hot water scheduling and the legionella cycle, and is usually the best room control too. Third-party heat pump compatible thermostats such as Hive and Engo send a simple on/off demand. Homely goes further and replaces the control strategy on supported models.
Pipe insulation and isolator
Outdoor pipes need thick, UV-resistant insulation fixed with rubber-lined clips. A lockable rotary isolator beside the unit lets an engineer cut the power safely.
Sizing a heat pump properly
The right size is the heat your home loses on the coldest design day, not its floor area or the size of the old boiler. That figure, the design heat loss, depends on insulation, glazing, air-tightness, room temperatures and the outdoor design temperature for your postcode. MCS installers calculate it room by room to the MIS 3005-D standard.
Oversizing costs you twice. A bigger unit is more expensive to buy, and in mild weather it cycles on and off instead of ticking over, which wears the compressor and lowers efficiency. Undersizing leaves rooms cold at the design temperature and leans on the immersion or backup heater. The kit builder picks the smallest output at or just above your design load for exactly this reason.
Rule of thumb only: a well-insulated 1990s three-bed semi often needs 5–7kW; an older solid-wall detached home can need 10–14kW. Use the estimate to shortlist, then confirm with a survey.
Flow temperature and your radiators
Heat pumps are most efficient at low flow temperatures, typically 35°C for underfloor heating and 45–50°C for radiators. At those temperatures a radiator gives out roughly half of its catalogue rating, which is quoted at a much hotter 75/65°C. Some rooms may need larger or double-panel radiators; the heat loss survey will show which. Our radiator guide and underfloor heating guide cover emitter choice in more depth.
Weather compensation
Every heat pump in the builder supports weather compensation. You set the flow temperature needed at your design outdoor temperature and at a mild day; the controller slides between them as the weather changes. Set up well, it is the single biggest factor in running costs.
Monobloc or split, R290 or R32
A monobloc keeps all refrigerant in the sealed outdoor unit and runs water pipes into the house. No F-gas qualified engineer is needed to connect it, which makes it the usual choice for UK homes and the type the kit builder covers.
A split or hydro split system runs refrigerant pipes to an indoor hydro unit. It suits long pipe runs and keeps water pipes away from frost, but needs F-gas certified installation. Panasonic’s Aquarea L Generation hydro split indoor units are an example. For split systems, ask us for a quote.
| R290 (propane) | R32 | |
|---|---|---|
| Global warming potential | 3 | 675 |
| Maximum flow temperature | Up to 70–75°C on most current models | Typically 55–65°C |
| Where it suits | Retrofits with existing radiators; future-proof against F-gas phase-down | Well-insulated homes and underfloor heating; often lower purchase price |
| Siting | Keep clear of drains, openings and ignition sources as the manual specifies, because propane is flammable | Standard monobloc clearances |
Higher possible flow temperatures don’t mean you should run at them. Even an R290 unit is cheapest to run at the lowest flow temperature that keeps the house warm.
The brands we stock
Our four main heat pump brands are listed first in the kit builder. Each has its own rules for controllers and cylinders, and the builder applies them for you.
Panasonic Aquarea
J Generation R32 monobloc 5–9kW, T-CAP J 9–16kW, M Series T-CAP R290 9–16kW
- J Generation units include their own controller. With a non-Panasonic cylinder, add the PAW-TS2 tank sensor. The Aquarea 192L cylinder comes with its sensor.
- M Series R290 units need an indoor control module: WH-CME5 for single-phase 9 and 12kW, WH-CME8 for three-phase.
- T-CAP models hold their rated output down to very low outdoor temperatures, useful for colder sites.
- Panasonic anti-freeze valves are an alternative to glycol.
Grant Aerona
Aerona 290 R290 monobloc: 4, 6.5, 9, 12 and 15.5kW
- A straightforward monobloc that pairs with any quality heat pump cylinder in our range.
- R290 allows higher flow temperatures, which helps retrofits keep more of the existing radiators.
- Grant offers extended guarantees when installed by one of its G1 approved installers.
Mitsubishi Electric Ecodan
R290 PUZ-WZ 5–12kW, R32 PUZ-WM 5–11.2kW, Zubadan 14kW, coastal-protected versions
- Ecodan outdoor units need an FTC controller. Ecodan FTC7 pre-plumbed and packaged cylinders include the controller, primary pump and valves.
- With another make of cylinder, add the FTC7 master controller (PAC-IF082B-E), the cylinder sensor (PAC-TH011TK2-E) and a primary pump. The builder does this automatically.
- BS coastal models have extra corrosion protection for sites near the sea.
Samsung EHS
Mono Gen 7 R290 5–16kW (Standard and Integrated), HT Quiet R32 8–14kW, R32 16kW single and three-phase
- Standard monoblocs need a controller, such as the MIM-E03FN AI Home kit, and an external primary pump that takes its speed signal from the Samsung board.
- The Mono ClimateHub combines cylinder, hydro components and controls in one indoor unit, and only works with Samsung outdoor units.
- Communication between outdoor unit and controller needs screened cable, such as 1mm² CY.
Other heat pump brands
The kit builder also includes every other air source heat pump we stock. Choose “Other brands” in step 2 to see them. Some need the manufacturer’s own interface or controller, and the builder flags this.
Choosing a hot water cylinder
Because a heat pump stores water at a lower temperature than a boiler, you need a little more of it. Allow roughly 45 litres per person, with a 150L minimum and more for extra bathrooms or a large bath.
| Household | Typical cylinder | Notes |
|---|---|---|
| 1–2 people, 1 bathroom | 150L | Slimline models suit small airing cupboards |
| 3–4 people, 1 bathroom | 200–210L | The most common size |
| 4–5 people, 2 bathrooms | 250–260L | Allows back-to-back showers |
| 5+ people, 2–3 bathrooms | 300L+ | Check coil size against heat pump output |
Standard or pre-plumbed
A standard heat pump cylinder is just the vessel and its coil; the installer adds the diverter valve, expansion vessel and controls. A pre-plumbed cylinder arrives with these fitted and wired, which saves hours on site. Some, such as the Telford Tempest with a 50L integrated buffer and Ideal HP290 buffer and low loss header versions, also include the hydraulic separation. Horizontal models like the Telford Tempest horizontal range fit lofts and low spaces.
Browse the full ranges: heat pump cylinders and pre-plumbed heat pump cylinders.
Legionella protection
Stored hot water must reach 60°C regularly. Heat pump controllers run a weekly pasteurisation cycle, usually topped up by the immersion heater. Schedule it early in the morning on a mid-week day, when the water is already warm.
Frost protection: glycol or anti-freeze valves
Water sits in the outdoor unit and its pipes all year. If the power fails in a freeze, the heat pump can’t run its own frost protection, so the system needs a fallback.
Glycol mixes an inhibited antifreeze through the whole system. It protects even during long power cuts and adds corrosion protection. It slightly lowers heat transfer, raises pump demand, and the concentration should be checked at each service. We stock Thermox DTX and Sentinel R600. The kit builder works out drums from your estimated system volume at the concentration you choose; check each product’s datasheet for the protection it gives at that mix.
Anti-freeze valves keep the system on plain water. Fitted at the lowest outdoor point on flow and return, such as the Intatec ZERO, they open and dump water if it nears freezing. The system then needs refilling and re-pressurising, and a normal inhibitor is added instead of glycol. Check the heat pump manufacturer accepts them.
Either way, clean the system before commissioning. Old systems benefit from a power flush; browse our central heating chemicals for cleaners, inhibitors and biocides.
Electrical supply and isolation
A heat pump needs its own circuit from the consumer unit, sized to the maximum running current in the installation manual. Most single-phase domestic units up to 16kW sit on a 16–32A circuit. A local isolator beside the unit is required so it can be safely switched off for service, and it must be rated at or above the circuit protection.
- Single-phase: a 32A three-pole outdoor isolator such as the Scame IP66/IP69 covers units up to 16kW.
- Three-phase: use a four-pole isolator, such as the IMO STAG range.
- Controllers, hydro kits and pre-plumbed cylinders often need their own fused supply too.
- Tell your electricity network operator before connecting. Most accept a simple notification for domestic heat pumps.
Electrical work must meet BS 7671 and be notified under Part P, so use a qualified electrician.
Grants and MCS
In England and Wales, the Boiler Upgrade Scheme takes £7,500 off an air source heat pump installation. At the time of review, homes replacing oil or LPG heating can get £9,000 until 31 March 2027. Scotland runs its own grant and loan scheme through Home Energy Scotland.
The grant is claimed by an MCS-certified installer, who must design and commission the system. If you are buying equipment for a grant-funded job, agree the kit with your installer first. For more on funding, see our grants FAQs.
Heat pump FAQs
What size heat pump do I need?
One that matches your home’s design heat loss, the heat it loses on a very cold day. A rough estimate for a typical three-bed semi is 5–8kW, but insulation and age make a big difference. Use the kit builder to shortlist, then confirm with a room-by-room heat loss survey.
Do I need a buffer tank?
Not always. Many systems work best direct, with the heat pump connected straight to the heating. You need extra volume when the system holds too little water for defrosting, and hydraulic separation when heavy zoning, such as underfloor heating with many actuators, could choke the flow. The kit builder recommends a layout, and you can change it.
Should I use glycol or anti-freeze valves?
Glycol protects the system even during a long power cut and needs no refill afterwards, but it slightly reduces efficiency and must be checked at services. Anti-freeze valves keep the system on water but dump it if it approaches freezing, and the system then needs refilling. Check what the heat pump manufacturer approves.
Can I keep my existing radiators?
Often, yes. At heat pump flow temperatures radiators give out roughly half their rated output, so some rooms may need a larger radiator. The heat loss survey shows which. R290 heat pumps can run hotter when needed, which helps retrofits.
Can I use any cylinder with any heat pump?
Most heat pump cylinders work with any monobloc, as long as the coil is large enough. Some are brand-locked because they contain the controller and hydraulics, such as Mitsubishi Ecodan FTC7 cylinders and Samsung ClimateHub. The kit builder only shows cylinders that suit your chosen heat pump.
What is the difference between R290 and R32?
They are refrigerants. R290 is propane, with a global warming potential of 3, and supports higher flow temperatures. R32 has a GWP of 675 and is widely used in well-established models. Both are efficient; R290 is the more future-proof choice.
Can I install a heat pump myself?
Monobloc units need no refrigerant work, but the installation involves plumbing, unvented hot water and electrical work that must meet Building Regulations. Unvented cylinders need a G3-qualified installer, and electrical work must be done under Part P. To claim the Boiler Upgrade Scheme grant, an MCS-certified installer must carry out the work.
How much is the Boiler Upgrade Scheme grant?
£7,500 off an air source heat pump in England and Wales. At the time of review, homes replacing oil or LPG heating can get £9,000 until 31 March 2027. Your MCS installer applies and deducts the grant from the quote.
Do I need a three-phase supply?
No. Almost all domestic heat pumps up to 16kW run on a normal single-phase supply. Three-phase versions exist for larger outputs and for properties that already have it. Choose your supply in step 2 to see the right models.
What controls come with the heat pump?
It depends on the brand. Some units have the controller built in; Samsung standard monoblocs need a separate control kit; Mitsubishi Ecodan uses an FTC controller that is inside Ecodan cylinders or bought separately. The kit builder adds the right one for your combination.
Fitting heat pumps for your customers?
Join the AIZO Partner Program. Send customers a kit built here, or order it yourself, and earn commission on every sale. Trade discounts are available case by case on larger or repeat orders.
- Commission on referred orders
- Direct line to our technical team
- Help with specifying larger and three-phase systems
Last reviewed: September 2026. This guide gives general guidance only. Always follow the manufacturer’s installation manual, and have the system designed by a competent, MCS-certified installer.