When we moved into our Derbyshire home in April 2014, it was already a work in progress. The ground floor was insulated and heated with a wet underfloor system, while the upstairs had two heating circuits: one for the two bathrooms and another for the three bedrooms and hallways. Although the house felt a little small for our needs at the time, it came with planning permission for an extension. We began the extension in 2015 and completed it in early 2018, increasing the house size to 450m². The ground floor continued to use underfloor heating, while the five bedrooms and five bathrooms were heated by radiators on separate circuits.

The house is well-insulated, with walls built to modern standards (using thermalite blocks and 100mm insulation) or dry-lined plasterboard inside thick, rendered old walls. The lofts are also well-insulated. However, the 11 exterior doors remain the weakest point in terms of insulation, despite all windows and doors being double-glazed. We also have four solid fuel fires, which we use sparingly during the coldest months of December through February.

Energy Efficiency Challenges

Despite our efforts to keep heating costs manageable (never heating the house above 20C and setting the water temperature to 55C) the running costs were significant. My usual approach was to encourage everyone to “put on a jumper,” tape up the immersion switch, lock down the nine thermostats, and turn the TRVs (thermostatic radiator valves) down to 2 or 3. While our system wasn’t inefficient, it was powered by an LPG boiler (first a Glowworm, then a Vaillant, replaced in 2020). LPG proved expensive and difficult to source, with prices rising steadily. By 2022, the cost per kWh had reached 5p, and it was clear that prices would only continue to climb.

The Turning Point: Embracing Renewable Energy

Our journey toward renewable energy began in 2016 when Octopus Energy took over our failing electricity supplier. Their innovative tariffs made solar panels, batteries, and two-way inverters increasingly attractive. Although I had installed a 4kW solar system in a previous home, the economic case for solar at this property only became viable in early 2023, as panel and battery prices dropped.

Key milestones in our journey include:

• Completing the extension in March 2018.
• Replacing the gas hob with an induction hob in November 2019 for better air quality and ease of use.
• Installing a smart meter in March 2022, enabling 30-minute interval monitoring.
• Transitioning to a full electric vehicle (EV) in September 2022.
• Installing 29 solar panels (10kW peak) and two 5kWh batteries with a two-way inverter in March 2023.
• Moving to the Agile Octopus tariff with export capabilities, despite a challenging process.
• Replacing the front door in August 2023 to improve insulation.
• Flooding during Storm Babet in 2023, which led to replacing 70m² of carpeted floors with stone.
• Replacing the LPG system in January 2025 with two Mitsubishi Ecodan cascade air source heat pumps (17kW total), a new plant room and a hot water tank.
• Adding a third 5kWh battery to optimise low-cost electricity imports and mitigate peak prices.
• Switching to the Cosy Octopus tariff in February 2025.

Energy Usage and Cost Analysis

Our investments in solar panels and air source heat pumps totalled around £30k, with a long payback period anticipated. However, these changes have allowed us to maintain energy costs close to 2022 levels, despite rising prices.

• 2022:
  Cost: £3,758 | Usage: 39.7MWh | Average cost: 9.5p/kWh
  Heating was heavily used from November to April, with minimal usage from May to September.
• 2023:
  Cost: £4,253 | Usage: 36.5MWh | Average cost: 11.7p/kWh
  The installation of solar panels and batteries reduced net usage from 10.7MWh to 7.5MWh. Time-of-use tariffs were exploited in Q4.
• 2024:
  Cost: £3,020 | Usage: 30.6MWh | Average cost: 9.9p/kWh
  Batteries and solar panels helped absorb price inflation, with net electricity imports dropping to 1.5MWh.
• 2025 (so far):
  Cost: £880 | Usage: 5.3MWh | Average cost: 16.7p/kWh
  Target: 12MWh (COP 3) at 12p/kWh. Energy usage in January and February has significantly reduced compared to previous years.

Key Takeaways and Lessons Learned

Our journey has been a steep learning curve, with several unexpected challenges and valuable lessons:

• ASHP Performance: I knew that running an air source heat pump would differ from a gas boiler’s on-off cycling, but I underestimated the complexity of a cascade system. The ASHP struggles to heat the house from zero to 20°C, and defrost cycles every 40 minutes reduce efficiency during freezing conditions. Installing an ASHP in frosty weather is not ideal.
• Frost Damage: I didn’t anticipate frost damage to the concrete plinth under the ASHP, which now needs to be redone.
• Air Quality and Circulation: Constant temperatures led to mustiness, as the gas system’s heating and cooling cycles had previously forced more thermodynamic circulation. We now leave internal doors open to encourage airflow and often open windows during good weather to improve air quality. This has prompted us to consider installing an internal air circulation system.
• Thermostats and TRVs: I hadn’t fully grasped that thermostats and TRVs now act as limiters rather than controllers. They switch off if temperatures exceed 22°C, and the system runs on weather compensation, aiming for 20°C.
• Monitoring Challenges: Measuring consumption or COP with a cascade system is difficult, as neither the MELCloud app nor the control panel provides accurate data. I now estimate based on the Solar app, assuming my non-ASHP electrical load in 2025 matches 2024. Thankfully, the Sunsynk app is excellent; without it, I’d be lost.

How the Renewable Heating Hub Forum Helped

The Renewable Heating Hub forums were invaluable in troubleshooting and optimising our system:

1. Heat Transfer Issues: I learned that a release valve pumps heat back outside if the system encounters too much friction (e.g., closed or blocked valves). This explained why we were generating heat that wasn’t transferring to the house – effectively heating Derbyshire in January!
2. System Settings: The initial setup had the hot water and heating temperatures set too high, causing repeated cycling. Weather compensation wasn’t enabled during installation, but forum advice helped me adjust the settings for better efficiency.
3. UFH Valve Fix: With confidence gained from the forum, I manually released a stuck underfloor heating (UFH) valve using a radiator key. The rush of water into the circuit was a moment of elation and relief, saving us the cost of draining and clearing the system.
4. Encouragement to Meddle: The forum gave me the confidence to tinker with the system, which has been crucial in resolving several issues.

The Installation Process: A Mixed Experience

The installation of the air source heat pump and associated systems was a mixed bag, with both positive and negative aspects.

The Good:

• The plumbing quality is good, and the system works well after some adjustments.
• I believe the COP is favourable, though accurate measurement remains challenging.

The Bad:

• Poor Insulation: The pipe insulation was subpar, and I had to redo most of it myself.
• Faulty Equipment: One of the Ecodan units was faulty out of the box and had to be replaced. The installers initially dismissed our concerns but eventually confirmed the fault.
• Installation Errors: A pump valve was left closed during commissioning, preventing heat from circulating in January. I discovered and fixed this myself.
• Workmanship Issues: The installers repeatedly left doors open in freezing weather, used crowbars to rip up floors, and left holes under carpets. Woodwork and wiring were poorly executed, with control units installed too close to door jambs, preventing doors from closing.
• Commissioning Failures: No proper commissioning or training was provided, and we were simply told “not to meddle.”
• Battery Delays: The incorrect battery was delivered initially, and it took a month to source the correct one. The leads were too short, adding further delays.
• LPG Tank Removal: I hadn’t factored in the £1,000 + VAT cost to remove Calor’s buried LPG tank from our front lawn.

Looking Ahead

Despite the challenges, our journey has been rewarding. The system is now operational, and we’ve significantly reduced our energy costs and environmental impact. However, the installation process highlighted the importance of thorough planning, skilled workmanship, and accurate monitoring. Future improvements may include enhancing air circulation systems and further optimising settings to maximise efficiency.

While the road hasn’t been smooth, we’re proud to have transformed our home into a more sustainable and energy-efficient space. The lessons learned (and the support from the Renewable Heating Hub forums) have been invaluable in navigating this complex but worthwhile journey.