Air-to-water heat pump installation

In the price list, installation means the heating engineer's labour for placing and connecting one air-to-water heat pump. It typically covers:

• placing the outdoor unit on a prepared base, plinth or wall bracket, including levelling and anti-vibration pads,
• fitting the indoor unit, hydraulic module or a compact unit with an integrated cylinder,
• connecting the outdoor and indoor parts hydraulically and connecting them to the heating circuit and hot water production,
• fitting the valves and fittings that belong to the heat pump, such as a strainer, isolation valves, safety valve and air vents,
• routing the condensate drain from the outdoor unit,
• filling, venting and pressure testing the circuit,
• first start-up, basic setup of the controls and a handover briefing for the owner.

What installation does not normally include: the heat pump itself, the cylinder, the buffer tank, the concrete base, trenching for pipes, the electrical supply and the inspection of the electrical installation. The power connection is done by a qualified electrician. With a split system, where refrigerant pipes are joined on site, only a technician certified to handle fluorinated greenhouse gases may open and charge the refrigerant circuit. With a monobloc, the refrigerant is sealed inside the outdoor unit at the factory, and only water flows between the units.

For many brands, such as Daikin, Mitsubishi Electric, Panasonic, Vaillant, Viessmann or NIBE, commissioning is carried out by the manufacturer's authorised service technician or a certified partner. An extended warranty often depends on it. Before signing the contract, check who does the commissioning and whether it is included in the price.

In a new build, the heat pump is usually installed after plastering and screeding, once the house is weathertight and the heating pipework is finished. In a renovation, the heat pump is often connected to the existing radiators. In that case it should first be checked whether the radiators can heat the house at a lower water temperature. A heat pump is most efficient with a low flow temperature, ideally with underfloor heating. Old radiators sized for 70 to 80 °C may not be enough in very cold weather.

Before the installation team arrives, these items should be ready:

• A heat loss calculation for the house. Without it, the heat pump output is only a guess. An oversized unit cycles on and off frequently, while an undersized one runs for long periods on the electric backup heater in cold weather.
• A base or bracket for the outdoor unit. A concrete strip, block or plinth, high enough to stay above the usual snow level at the site.
• A wall penetration. A core-drilled hole or sleeve for pipes and cables, ideally prepared during the shell construction.
• Condensate drainage. A gravel soakaway or a connection to the rainwater or foul drainage. According to manufacturers, an outdoor unit can produce dozens of litres of condensate a day in winter.
• Electrical supply. A dedicated, protected circuit to the manufacturer's specification, and agreement with the grid operator if the main fuse or the tariff is to be changed.
• Space for the indoor unit. A plant room with access to the pipework, a drain for the safety valve and room for servicing.

Positioning the outdoor unit

This is the most important decision of the whole job. The unit needs an unobstructed air supply, and the cold exhaust air must not be drawn back into the intake. Manufacturers advise avoiding corners and spaces between two walls, because reflections amplify the noise. Spots under a bedroom window, next to a terrace or right on the boundary with a neighbour are also unsuitable. If snow or ice can slide off the roof, the unit needs a canopy. With R290 refrigerant, which many newer monoblocs use, the manufacturer defines a safety zone around the unit where there must be no drains, light wells, ventilation openings or basement entrances, for example.

Placing on a base or bracket

The unit is set on a concrete base, a plinth or a load-bearing wall bracket. It must be level, with anti-vibration pads under the feet. A wall bracket is a compromise. It saves space, but on lightweight walls or a bedroom wall it can transmit vibration into the house. Most heating engineers therefore prefer a separate base on the ground.

Hydraulic connection

Insulated pipes run between the outdoor and indoor units. Outdoors, the insulation must resist moisture and UV radiation. Flexible hoses that dampen vibration are fitted at the connections, together with a strainer that protects the heat pump's heat exchanger from dirt in the system. When connecting to an old system, it pays to flush the pipework first and add a magnetic dirt separator. Sludge from old radiators is a common cause of faults.

Connecting to heating and hot water

Depending on the design, the heat pump is connected directly to the heating circuit or via a buffer tank or low loss header. Hot water is produced through a diverter valve and a cylinder with a sufficiently large coil. A standard cylinder intended for a boiler often has a coil that is too small, and the water then gets topped up by the electric immersion heater. Manufacturers also specify a minimum water volume in the system and a minimum flow rate that must always be guaranteed, even when the thermostatic radiator valves are closed.

Condensate and frost protection

The condensate drain is routed to a gravel soakaway below frost depth, to the rainwater drain or through a trap into the foul drainage. The outdoor section of the drain needs frost protection, often a trace heating cable. If the outdoor hydraulics are not protected against frost and the heat pump stops during a power cut, the water in the heat exchanger can freeze. Solutions include antifreeze, anti-freeze valves or separating the circuit according to the manufacturer's instructions.

Filling, pressure test and start-up

The circuit is filled with treated water, vented and pressure tested. The electrician completes the power connection and the technician starts the heat pump. The settings include the weather compensation curve, meaning how the flow temperature depends on the outside temperature, hot water production, the anti-legionella programme and time schedules. Finally, the commissioning report is completed.

Monobloc

The entire refrigerant circuit sits in the outdoor unit. Only water pipes enter the house. Installation is simpler and no F-gas certificate is needed. The downside is that the outdoor water pipes must be protected against frost and the distance between the units is usually limited.

Split

The compressor is outside, and the water-to-refrigerant heat exchanger is inside. Refrigerant pipes, which cannot freeze, run between the units. However, the circuit is joined, evacuated and charged on site, and only a certified technician may do this. A split is often chosen when the outdoor unit stands further from the house.

Hybrid system

The heat pump works together with the existing gas boiler, which only switches on in the coldest weather or when hot water demand is high. In renovations this can be a sensible intermediate step if the house is not yet insulated.

Equipment prices vary widely by output and brand. For typical family house outputs, the unit costs several thousand euros, plus the cylinder, buffer tank and accessories. Only a quote for the specific house gives an exact figure.

• Output based on a guess. In practice, the heat pump is sometimes chosen by floor area or by the output of the old boiler. Old boilers are usually heavily oversized, and an insulated house needs far less heat.
• Unit in the wrong place. Under a bedroom window, in a corner between walls or facing the neighbour's terrace. Noise then has to be dealt with later and at higher cost.
• Condensate discharged onto the ground. The water freezes in winter, ice builds up under the unit and can damage the evaporator or the path.
• Outdoor unit with no clearance above the ground. Snow blocks the air intake or the condensate drain, and the heat pump struggles during defrosting.
• Old system not flushed. Sludge and magnetite clog the strainer and heat exchanger within the first season.
• Small coil in the cylinder. Hot water takes a long time to heat and the immersion heater tops it up, which increases consumption.
• Thermostatic valves in every room without a bypass. The heat pump has no guaranteed minimum flow and reports faults.
• Factory settings left in place. The weather compensation curve stays unnecessarily high and the heat pump runs less efficiently than it could.

Check with your local authority whether your project needs a permit or a notification before installation. In an apartment building you will need the consent of the other owners, because the facade and roof are usually common parts of the building.

Noise from the outdoor unit must meet the limits that apply towards neighbouring houses, especially at night. Complaints from neighbours can lead to costly changes after the fact. Manufacturers therefore state the sound power level of the unit and recommended distances, which are worth respecting at the design stage.

The electrical connection must be carried out by a qualified electrician and followed by an inspection or test certificate. If the main fuse needs upgrading or you want a special heat pump tariff, arrange this with your grid operator in advance.

Many European countries support heat pumps through grants, tax relief or low-interest loans, usually on condition that the unit meets efficiency requirements and that a qualified or certified installer does the work. The rules change frequently and applications often have to be submitted before the work starts, so check current conditions on the official national or regional portal before you place an order.

At handover, ask for the commissioning report, the warranty terms and the electrical test certificate. Then go through these points:

• the outdoor unit is level, on anti-vibration pads and with enough clearance above the ground,
• the clearances around the unit match the manufacturer's instructions, and the exhaust air does not blow at a wall or towards the neighbour,
• the condensate drains into the soakaway or the drainage and does not run onto the path,
• the outdoor pipes are fully insulated, the insulation is undamaged and protected from the sun,
• the wall penetration is sealed and water cannot get in,
• a strainer and isolation valves are fitted on the heat pump inlet and are easy to reach for servicing,
• the system pressure does not drop after the test and nothing drips from the fittings,
• the controls are set up, you know how to change the temperature and mode, and you have the login details for the app,
• the heat pump makes no unusual noise or vibration that is transmitted into the house.

During the first winter, keep an eye on electricity consumption and on the hours the electric backup heater runs. If it runs often even in mild frost, something is wrong with the settings or the sizing.

The labour price in the NUMIQ price list is €950 per unit for one air-to-water heat pump. This covers the heating engineer's labour including minor consumables, without the heat pump itself, the cylinder, the buffer tank or other main materials. Prices vary by country, region and city.

The final cost of installation depends mainly on:

• the distance between the outdoor and indoor units and how the pipes are routed,
• whether it is a new build with prepared pipework or a replacement in an old system that needs flushing and alterations,
• the number of heating circuits, a buffer tank, a cylinder and a hybrid connection with the old boiler,
• removal and disposal of the old boiler,
• access to the installation site and the need for scaffolding or a lifting platform for a wall bracket,
• building work such as the base, wall penetrations and trenches for pipes.

Related work can be priced separately, for example gas or electric boiler removal, expansion vessel installation or laying underfloor heating pipes. You will find an overview of all items under heating work.