Air Source Heat Pump Installation Day: What Actually Happens
A standard air source heat pump installation in a Lancashire home takes two to four days, with the outdoor unit typically operational by the end of day two. The process involves more than just fitting a box outside your house – your heating system is essentially being re-engineered to work at lower temperatures, with new controls, pipework modifications, and often a hot water cylinder installation. Knowing what to expect each day helps you prepare and reduces the disruption to your household.
Before Installation Day: The Survey and Design Phase
Four to eight weeks before installation, your qualified installer will have completed a detailed survey of your home. This includes room-by-room heat loss calculations, assessment of your existing radiators, electrical supply check, outdoor unit placement planning, and hot water cylinder sizing. For Lancashire homes, the surveyor pays particular attention to the property’s exposure to weather (elevated homes in Rossendale or the Pennine foothills may need a slightly larger unit than sheltered properties in central Preston) and noise considerations for neighbours.
Before the installation team arrives, make sure the area where the outdoor unit will go is clear and accessible. This typically means a concrete pad or paving at the side or rear of the property, with at least 300mm clearance on all sides and 1 metre from any opening windows. For terraced houses in Blackburn, Burnley or Bolton, the unit usually goes in the back yard. For semis and detached homes, the side passage is the most common location.
You also need to prepare indoor space for the hot water cylinder if one is being installed. This is typically an airing cupboard, utility room or garage. The cylinder is around 1,800mm tall and 500mm to 600mm in diameter, so it needs a reasonable footprint. If your old gas boiler is being removed from inside, that sometimes frees up the space needed.
Day One: The Big Changes
Day one is the busiest and most disruptive. The installation team (typically two to three engineers) will arrive between 8am and 9am. The first tasks involve isolating your existing heating system and draining the radiator circuit. If you have a gas boiler being replaced, the gas supply will be capped off. This means you will have no heating or hot water from the moment work begins until the heat pump is commissioned, so plan accordingly – in winter, consider whether you need temporary heating for the household.
The outdoor unit base is prepared – either a concrete plinth (poured in advance or pre-cast) or anti-vibration mounting feet on existing hard standing. The unit itself weighs 60 to 120kg depending on the model, so the team will use appropriate equipment to position it. The refrigerant lines (insulated copper pipes) are run from the outdoor unit to the indoor connection point, typically through an external wall. A core drill creates the penetration, which is sealed and weatherproofed after the pipes are threaded through.
Inside, the hot water cylinder is installed and connected to the pipework. If you are keeping your existing cylinder, it may need a new coil or immersion heater to work with the heat pump. Most Lancashire installations involve fitting a new unvented cylinder specifically designed for heat pump use, which stores water at mains pressure and eliminates the need for a header tank in the loft.
By the end of day one, the outdoor unit is in place, the refrigerant lines are connected, the cylinder is installed, and the main pipework modifications are largely complete. The house may feel like a construction site, with dust sheets, tools and exposed pipework.
Day Two: Electrical Work and Commissioning
Day two focuses on the electrical connections and system commissioning. The heat pump requires a dedicated electrical supply, usually a separate circuit from your consumer unit rated at 16A to 32A depending on the unit’s size. An electrician (electrically qualified) will install the circuit, fit an isolator switch near the outdoor unit, and connect the controls wiring.
The heating system is filled with water, pressurised, and tested for leaks. Any radiator modifications – new TRVs, replaced radiators, or additional radiators identified during the survey – are completed. The system is flushed to remove debris and a corrosion inhibitor is added, just as with a conventional boiler installation.
The refrigerant circuit is pressure-tested and, if not pre-charged, the refrigerant is added. This is a controlled process carried out by a qualified refrigerant engineer. The indoor and outdoor units are powered up and the commissioning process begins – checking refrigerant pressures, testing the defrost cycle, verifying heat output at various flow temperatures, and programming the controls.
By the end of day two, you should have heating and hot water. The system may not be fully optimised – that takes time and adjustment – but it will be functional. The installer will set initial heating schedules and explain the basic controls.
Day Three (If Needed): Finishing and Fine-Tuning
Some installations, particularly more complex ones involving extensive pipework changes, multiple radiator replacements, or underfloor heating connections, require a third day. This is common in larger Lancashire properties and in older homes where the existing pipework layout does not easily accommodate the heat pump configuration.
Day three typically covers finishing plasterwork around pipe runs, making good any disruption to walls or floors, completing the installer certification paperwork, and walking you through the system in detail. The installer should explain the weather compensation curve (which adjusts the flow temperature based on outdoor conditions), the hot water schedule, the boost function for extra heating, and the monitoring app or display.
The installer will also complete the installer certification notification and register the system with your local council’s Building Control department (or through an approved competent person scheme). This documentation is essential for claiming the government grant and for future property sales.
The First Few Weeks: What to Expect
Your heat pump will not feel like your old gas boiler, and adjusting to the difference takes time. A gas boiler produces a blast of very hot water that heats radiators quickly. A heat pump produces a steady flow of warm water (typically 40 to 55C) that heats the home gently and continuously. Think of it like the difference between a microwave (quick and intense) and a slow cooker (gradual and steady).
During the first few weeks, resist the urge to turn the thermostat up if the house feels slightly cool. Instead, let the system run for longer periods – many heat pump owners find that running the heating for extended hours at a low flow temperature is more comfortable and more efficient than short blasts at high temperature. Your installer should advise on the optimal schedule for your specific home and system.
Hot water may take longer to reach full temperature than with a gas boiler. Most heat pump cylinders heat from cold to 50C in one to two hours, with a top-up legionella cycle to 60C once or twice a week. If you are used to on-demand hot water from a combi boiler, the switch to stored hot water requires a minor adjustment to your routine.
Your electricity bills will increase because the heat pump runs on electricity, while your gas bills will decrease dramatically or disappear entirely. For the first quarter, monitor both to understand your new cost profile. Most Lancashire heat pump owners find their total energy costs are similar to or slightly lower than their previous gas and electricity combined, with the gap widening in favour of the heat pump as they optimise settings.
Common Installation Challenges in Lancashire Homes
Lancashire’s housing stock presents some recurring challenges. Older terraced houses in Burnley, Accrington and Darwen often have small back yards with limited space for the outdoor unit. Creative placement – mounted on a wall bracket, positioned in a corner, or installed in a small side alley – can solve this, but requires careful attention to noise regulations and airflow requirements.
Electrical supply limitations are common in older properties. Some Lancashire homes, particularly pre-war terraces, have single-phase electrical supplies that are already close to capacity. The heat pump (drawing 2 to 5kW) may require an electrical supply upgrade, adding £500 to £1,500 to the project. Your installer should check this during the survey.
Asbestos in old heating systems can cause delays. If your existing pipework, boiler flue, or cistern lagging contains asbestos (common in Lancashire homes built or renovated before 1985), specialist removal is required before the installer can proceed. This adds one to five days and £300 to £1,000 to the project depending on the extent.
How long does heat pump installation take?
A standard installation takes two to three days. More complex projects involving multiple radiator changes, underfloor heating, or extensive pipework modifications can take three to four days. The outdoor unit is typically operational by the end of day two, with the third day used for finishing and commissioning.
Will I be without heating during installation?
Yes, typically for one to two days. The existing heating system must be drained and the gas boiler disconnected before the heat pump can be installed. In winter, consider portable electric heaters for essential rooms. Some installers can stage the work to minimise the gap, keeping the old boiler running until the heat pump is ready to commission.
Do I need to be home during installation?
You need to be available for the start and end of each day to provide access and discuss any decisions that arise. Most installers are happy for you to be out during the middle of the day as long as the team can access all required areas. On the final day, plan to be present for the commissioning walkthrough and controls demonstration, which typically takes 30 to 60 minutes.
