Most straightforward air-to-water heat pump installations take between two and four days on site, once you include commissioning. A ground source system takes considerably longer because of the groundworks involved. What actually happens during that time surprises a lot of homeowners, mostly because it’s less disruptive than they expect. Here’s what to expect from the first survey through to the moment your new system is handed over.
What Happens During the Heat Pump Survey?
The survey is a technical visit, not a sales call: a qualified surveyor or engineer spends an hour or more in your property recording the details that everything else depends on. The accuracy of the quote, the equipment size, and your grant eligibility all rest on what’s recorded here. They’ll be looking at:
- Insulation levels: loft depth, wall construction and any cavity or external insulation, since this drives how much heat the property loses.
- Existing radiators: size, age and type, to work out which ones can stay as they are and which need upsizing for lower-temperature heat pump operation.
- Electrical supply: the condition of the consumer unit and whether the incoming supply can handle the additional load.
- Outdoor space: where the outdoor unit can sit, with enough clearance for airflow, noise regulations, and pipe runs back into the house.
- Hot water cylinder space: heat pumps need a cylinder, so the surveyor checks whether an existing one can be reused or where a new one will fit, typically in an airing cupboard, loft, or utility space.
This visit produces the raw data for a room-by-room heat loss calculation. That calculation tells us how much heat your home loses each hour on a cold day, and therefore what size heat pump and what flow temperature will keep you comfortable.
How Does the Survey Become a Design and Quote?
Once the heat loss calculation from the survey is complete, we turn it into an MCS-compliant heat loss report and a full system design. This isn’t a generic package. It specifies the exact heat pump model and output, which radiators need replacing or upsizing, cylinder size, pipe routing, and controls setup. MCS compliance matters because it’s the standard that underpins both the manufacturer warranty and eligibility for the Boiler Upgrade Scheme (BUS) grant.
As your installer, we handle the BUS grant application on your behalf as part of this stage. You don’t need to deal with Ofgem paperwork directly. The grant currently takes £7,500 off the cost of an air source or ground source heat pump installation in England and Wales, applied at the point of installation rather than as a rebate you claim back later.
From an accepted quote to an install date, lead times vary quite a bit depending on the time of year, equipment availability, and how much work like radiator changes or electrical upgrades is needed. It’s worth asking your installer for a realistic estimate specific to your job rather than assuming a fixed wait.
What Does a Typical Air-to-Water ASHP Installation Look Like Day by Day?
A typical air-to-water ASHP installation runs over three to four days on site, covering removal, indoor fitting, radiators and electrics, and commissioning. Every property is different, but a standard retrofit (replacing an existing gas or oil boiler with an air source heat pump, with moderate radiator changes) tends to follow this pattern.
What Happens on Day 1 of Installation?
Day one is about removal and groundwork: if you’re replacing an old boiler, the day starts with draining the heating system and removing the old unit and any redundant pipework or flue. Outside, the team prepares the base or wall bracket for the outdoor unit (this might be a concrete or plastic pad on the ground, or a bracket fixed to an external wall) and begins running the pipework that will connect the outdoor unit to the house. Expect some noise from drilling and cutting, and the heating will likely be off for part of the day.
What Happens on Day 2 of Installation?
Day two is largely indoor installation and first-fix electrics. The hot water cylinder goes in (or is connected, if one is already in place), along with the indoor unit or manifold, expansion vessels, and the pipework connecting everything to the heating circuit. Electricians carry out the first fix, running cables from the consumer unit to the outdoor unit and controls, without yet making the live connections.
What Happens on Day 3 of Installation?
Day three covers radiators, second-fix electrics, and controls: any radiators identified for replacement or upsizing during the survey are swapped out, along with associated pipework adjustments. Electricians complete the second fix, connecting up the outdoor unit, immersion backup (where fitted), and wiring in the heat pump controller and any smart thermostats or zone controls. By the end of day three, the system is physically complete.
What Happens on Day 4 of Installation?
Day four, where needed, is for commissioning, testing, and handover, the final and arguably most important stage. On straightforward jobs this can happen on day three instead; on larger or more complex installs it’s a separate day.
What Does Heat Pump Commissioning Actually Involve?
Commissioning involves the engineer setting the heat pump’s operating parameters (flow temperatures, weather compensation curves, cylinder settings) to match the MCS design produced at the quote stage, then testing the system under load. It isn’t just switching the system on and checking it runs: they also check pressures and flow rates through each circuit, verify there are no leaks, and confirm the heat pump is delivering the performance it was designed to deliver.
This step matters beyond just making sure the heating works. Successful commissioning is what triggers the MCS certificate for your installation, and that certificate is required both to release your BUS grant payment and to register your manufacturer warranty. Skipping or rushing commissioning isn’t just bad practice. It can leave you without the paperwork you need for the grant or a valid warranty claim later.
What Should You Receive at Handover?
At handover you should receive your MCS certificate, manuals, warranty confirmation, and a controls walkthrough, not just the installer packing up and leaving. Before they go, you should be given:
- Your MCS certificate, confirming the installation meets the required standard
- User manuals for the heat pump, cylinder, and any controls or smart thermostats fitted
- Confirmation that the manufacturer warranty has been registered in your name
- A walkthrough of the controls and any app, covering how to adjust temperatures, set schedules, and read basic fault codes
Take the time for the controls walkthrough even if you’re keen to get your kitchen table back. Heat pumps are typically run differently to a boiler, with steadier, lower-temperature heating rather than short blasts, and understanding that up front avoids a lot of “is it actually working?” phone calls in the first few weeks.
How Long Does a Ground Source Heat Pump Installation Take?
A ground source heat pump (GSHP) installation typically takes one to three weeks rather than a few days. The difference comes down entirely to what happens outside. A GSHP extracts heat from the ground via either a horizontal trench system, which needs a large area of garden excavated to around 1.2 metres deep, or vertical boreholes, which require specialist drilling rigs to go anywhere from 50 to 150 metres down.
Trenching or borehole drilling is weather-dependent, needs heavy plant access to your garden, and has to happen before any indoor work can really get going, since the ground loop has to be connected before the system can be tested. Once the groundworks are done, the indoor installation itself (cylinder, indoor unit, pipework, electrics, controls, commissioning) follows a similar pattern to an ASHP install, just added onto a longer overall project.
How Do ASHP and GSHP Installation Timelines Compare?
| Stage | Air Source Heat Pump (ASHP) | Ground Source Heat Pump (GSHP) |
|---|---|---|
| Groundworks | None. Outdoor unit sits on a small base or wall bracket | 1–2+ weeks for trenching or borehole drilling |
| Indoor installation | 1–2 days | 2–4 days, once groundworks are complete |
| Commissioning | Same day or following day | 1 day, after ground loop is connected and pressure-tested |
| Typical total on-site time | 2–4 days | 1–3 weeks |
| Weather sensitivity | Low | High. Groundworks can be delayed by wet or frozen ground |
| Garden disruption | Minimal, localised to unit position | Significant. Trenches or drilling rig access across the garden |
What Should You Expect on Each Day of Installation?
| Day | What’s Happening | What It Means for You |
|---|---|---|
| Day 1 | Old boiler/system removed, outdoor unit base prepared, initial pipework | Heating off for part of the day; drilling noise; access needed to boiler location and garden |
| Day 2 | Cylinder and indoor unit fitted, pipework connected, electrical first fix | Access needed to airing cupboard/utility space and consumer unit; some water off periods |
| Day 3 | Radiator changes, electrical second fix, controls fitted | Access needed to every room with a radiator being changed; some mess from pipework |
| Day 4 (if separate) | Commissioning, testing, handover | System tested under load; you’ll get your controls walkthrough and paperwork |
What Disruption Should You Actually Expect?
Expect drilling and cutting noise on the first day or two, dust sheets and some mess around radiator locations, your heating being off for periods, and hot water being unavailable while the cylinder is connected. It’s a building job, so there’s no pretending it’s silent and mess-free, but it’s typically far less disruptive than a full boiler system replacement with major pipework changes. Heating is rarely off overnight in colder months, as installers generally avoid leaving a home without heat. Installers will need access to every room where a radiator is being changed, plus the loft, airing cupboard or utility room, and obviously the garden or exterior wall where the outdoor unit goes.
How Should You Prepare Your Home Before Install Day?
Clear access routes, move furniture, arrange pets, and clear the outdoor unit space. A bit of preparation on your part makes the whole job faster and smoother for everyone:
- Clear access routes to the boiler location, loft hatch, airing cupboard, and any rooms with radiators being replaced.
- Move furniture away from radiators: a metre of clear space around each one being worked on avoids delays and protects your belongings from dust or knocks.
- Clear the outdoor unit location of pots, furniture, or storage, and make sure there’s reasonable access from the street or driveway for materials.
- Arrange pets for the day. Doors will be open, tools and materials will be around, and most pets are happier elsewhere or in a closed-off room.
- Plan around young children if possible, particularly on days with drilling or when the heating and hot water are off.
- Set aside valuables in rooms that will be worked in, simply as good practice whenever tradespeople are in and out of the house.
- Expect no heating overnight interruptions but check with your installer if you have specific medical or household needs that mean you need heating or hot water maintained at a particular point in the job.
None of this is complicated, but doing it before the van turns up on day one means the team can get straight to work rather than losing the first hour moving furniture themselves.
