For years, I’ve spent my professional career investigating technologies to reduce emissions: carbon capture and utilisation, direct air capture, waste-to-energy systems, and the integration of renewable electricity into heating and transport. But in my personal life, I remained largely unconverted. Last year, I faced an important question: Am I practising what I preach?

In 2024, I quantified my household carbon footprint and found it sobering: 1,789.77 kgCO₂/year from gas heating and electricity alone. When including transport, flights, water, and other Scope 3 activities, my total was 4,928.17 kgCO₂/year. This forced me to make a choice: continue as I was, or use the emerging evidence and policy support to systematically decarbonise my home.

I chose the latter.

This article documents the first full year of that transition.

The baseline

In my previous article, I established my household baseline using 2024 data:

• Scope 1 (direct gas combustion): 1,396.35 kgCO₂/year
• Scope 1 (petrol use): 1620.30 kgCO₂/year
• Scope 2 (purchased electricity, location-based): 393.42 kgCO₂/year
• Total Scope 1 & 2 footprint: 3,410.06 kgCO₂/year

This metric, including Scope 1 and Scope 2, has become the benchmark by which I measure progress on my path to net zero. For now, I intentionally left out the Scope 3 activities.

Consequently, in 2025, I made two critical interventions that helped me cut my operational emissions.

Heat pump and induction hob (April 2025)

The decision to replace my gas boiler was not trivial. The boiler, installed in my new home in late 2022, was relatively new and operating at ~92% efficiency. Replacing it required strong justification that went beyond the environment, encompassing economics and practical considerations. I discussed these at length in my previous article. Note, my old boiler has a 2nd life somewhere else.

The environmental maths was compelling. Gas heating was emitting approximately 1.4 tonnes of CO₂ per year. Over a 10–15-year boiler lifetime, this represented 14–21 tonnes of CO₂ that could be avoided by switching now. A heat pump running on grid electricity would emit roughly 82% less CO₂ per unit of heat delivered, reducing heating emissions by approximately 0.78 tonnes per year.

The Boiler Upgrade Scheme (BUS) provided me a £7,500 government grant, bringing my out-of-pocket cost for a 4 kW Daikin Altherma 3 ASHP with a 250 L hot water cylinder down to ‘merely’ £580. It was a no-brainer decision for my household. Without this subsidy, the economic benefits would have been much smaller, and I would be looking at a 10-year payback period.

Furthermore, given there was no point paying the standing charge for the gas supply just for cooking, I also replaced the gas hob with an induction cooktop (£379), eliminating the last combustion appliance in the home.

From April onward, my household imported zero kWh of gas.

Solar & battery storage (end July 2025)

I was sceptical about installing solar panels in North East England – but I was quickly proven wrong.

In July, I invested in a 9.4 kWp solar array of 20 × 470 W Aiko solar panels (split east–west), 10 kW SigEnergy Energy Controller, and 16 kWh of battery storage (two 8 kWh modules). At the same time, I got a Zappi EV charger installed as I am looking to change my car to a more environmentally friendly one in 2026.

This second intervention shifted my household from consumer to prosumer, capable of generating, storing, and selling electricity back to the grid. This costed me £12,500, with an expected payback period of 7 years. Unfortunately, no grants are currently available for solar & battery systems. However, I can already see the benefits of having an independent energy supply and flexibility to shift when I consume electricity from the grid if needed – more on this in another article.

Year 2025 in data

My annual energy consumption profile (January–December 2025) reflects the changes I made to my home energy system. Note that the solar-generated electricity represents only the period between August and December 2025. I expect next year to be much better!

For carbon accounting, I used the following 2025 emission factors:

• Gas emission factor: 0.2027 kgCO₂e/kWh
• Electricity emission factor: 0.126 kgCO₂e/kWh

Metric	Value (kWh)
Gas imported	3,028.7
Electricity imported	3,351.69
Solar generated electricity	2,401.67
Electricity exported	1,893.36
Estimated solar self-consumed	~508

No more dash for gas

My gas consumption stopped in April 2025, once the ASHP was installed and the gas boiler was removed. In the period from January to April, my household consumed 3,028.7 kWh of gas. These tend to be the coldest months of the year in my region. Yet, with cold snaps in November and December and temperatures below 0 °C, my new ASHP managed to keep my home warm and cosy at 21 °C while consuming a maximum of 10-15 kWh per day. As I can currently draw electricity at 14 p/kWh and store it in my batteries, I essentially pay 4.1 p/kWh of heat (sCOP 3.4). This demonstrates that the ASHP can meet all heating and hot water demands, at approximately 33% cheaper than gas (92% efficiency, unit cost 5.6 p/kWh, resulting in 6.1 p/kWh of heat).

The electricity paradox

My electricity imports rose from approximately 1,900 kWh (2024) to 3,351.69 kWh in 2025, which corresponds to a 76% increase. This is the central tension in household electrification: Why does moving to an electric heating system require more electricity?

The answer lies in thermodynamic efficiency and measurement boundaries. A gas boiler delivers heat at approximately 92% efficiency (i.e., 92 kJ of heat per 100 kJ of fuel energy). An air-source heat pump, operating at a seasonal coefficient of performance (sCOP) of 3.0–4.0, delivers 3.0–4.0 kJ of heat per 1 kJ of electrical energy. In kWh terms at the meter, this appears as a higher electricity demand. But in primary energy terms, the heat pump delivers the same comfort with less total energy input.

Category	2024	2025	Change	% Change
S1: Gas (kgCO₂e)	1,396.35	613.92	−782.43	−56.0%
S1: Petrol (kgCO₂e)	1,620.30	1,554.56	-65.74	-4.1%
S2: Electricity (kgCO₂e)	393.42	422.31	+28.89	+7.3%
Home Scope 1 & 2 emissions (kgCO₂e)	3,410.06	2,590.79	−819.27	−24.0

However, from a carbon footprint perspective, the ASHP is much more efficient. Even though electricity use rises by 7.3%, total home energy emissions fall by 24%. This occurs because the Scope 1 reduction (−28%) vastly outweighs the Scope 2 increase (+7.3%). The arithmetic works because the 2025 grid emission factor (0.126 kgCO₂e/kWh) is significantly lower than the gas factor (0.2027 kgCO₂e/kWh), making electric heating substantially cleaner than combustion.

Note that this advantage is conditional. Were I located in a coal-heavy region with a higher grid carbon intensity, the arithmetic would be different. Geography, grid composition, and time-of-use all matter profoundly in these decisions.

Operational carbon footprint

In my carbon footprint calculator, I treat exported electricity as “beyond scope,” with a separate line item of −238.56 kgCO₂/year, based on 1,893.36 kWh of export at 0.126 kgCO₂e/kWh. This would not normally be netted off against Scope 2 in the formal numbers according to the GHG Protocol. However, I find it helpful for describing the operational effect my PV system has on the grid. When I export solar electricity, someone else does not need to import electricity from a fossil-fuel plant.

This means that my household resulted in net emissions of 2352.23 kgCO₂/year, estimated as 2590.79 kgCO₂/year less 238.56 kgCO₂/year from solar export. Overall, this is 31% less than last year (Scope 1 & 2 only).

Solar generation and export

The solar array generated 2,401.67 kWh since installation at the end of July 2025. The seasonal distribution reveals the expected pattern:

• Winter months (Nov-Dec): Minimal generation (~50–90 kWh/month) due to low irradiance and short days.
• Spring, summer, and early autumn (Jul–Sep): Peak generation, with August alone producing 959.75 kWh, nearly 40% of the annual total (note this was not the full year of operation).

Of this, the household exported 1,893.36 kWh to the grid, retaining approximately 508 kWh for self-consumption. The core premise was financial: with time-of-use tariffs (i.e., Agile, Cosy), I can draw electricity at 2-14 p/kWh and sell my solar export at 15 p/kWh. For the full year, export revenue totalled £336.85, substantially offsetting my energy costs.

Cost Component	Amount (£/year)
Gas costs	199.68
Electricity costs	761.63
Export revenue	−336.85
Net electricity cost	424.78
Total net energy cost	624.46

An annual household energy cost of £624.46 is extraordinarily low by UK standards (typical: £1,200–£1,500 annually).

My energy cost last year was around £1,200. The transition has already reduced annual energy spent by nearly 50%. It means that my ASHP investment has already been paid back.

This reflects:

1. The heat pump’s efficiency at mild temperatures (spring/early autumn, where sCOP ~3.5–4.0)
2. The substantial solar export in the summer months
3. The lower consumption baseline of a relatively efficient home

Heat pump performance

With nearly 9 months of operation recorded, the data from the Daikin MMI indicates the following coefficient of performance:

• Heating COP: 4.0
• Hot water COP: 2.7

These values align with the system’s design specifications and typical field performance for comparable UK installations. The heating COP of 4.0 means that for every kWh of electrical energy consumed, the system delivers approximately 4 kWh of heat to the building. The hot water COP of 2.7 reflects the higher lift required to raise water temperature (typically from 30°C incoming to 46°C stored). The overall sCOP as of December 2025 was 3.4, which aligns well with Octopus design numbers. I am happy with these numbers, particularly given that the ASHP performs surprisingly well in sub-zero conditions, but I still have room for improvement (i.e., radiator balancing and operating conditions).

What worked well

1. The heat pump eliminated gas entirely after March.

This is a structural change, not a marginal improvement. The inflection was clean and decisive. The ASHP was sized appropriately (4 kW) for my home’s heating needs in the UK climate, and installation and commissioning were completed professionally in three days.

2. East–west solar orientation extended the generation window.

By splitting the array 50–50 between east and west aspects, I achieved a broader generation profile than a purely south-facing array would. Peak generation now spans roughly 7 am to 7 pm in summer, rather than the narrower 10 am to 3 pm profile of south-only systems. This reduces the pressure on battery cycling and improves the potential for self-consumption.

3. Real-time visibility changed behaviour.

The SigEnergy controller and Home Assistant integration transformed energy from an abstract monthly bill into real-time data. I now observe when solar is available, when the battery is charging, and when exports are happening. This visibility shifted my behaviour: I now schedule high-consumption tasks (washing, dishwashing) into high-solar windows or cheap-tariff periods. This behavioural change is hard to quantify but very real.

4. The Daikin ASHP performed to specification.

With a heating COP of 4.0 and hot water COP of 2.7 across the year, the unit delivered consistent performance. The system operates quietly, maintains stable heating without short-cycling, and integrates seamlessly with the existing hot water system.

Known Unknowns and Unknown Unknowns

Known Unknowns

These are gaps I’ve identified and can investigate:

• Accurate seasonal COP profile under controlled conditions: I need proper instrumentation, including heat meters, outdoor air temperature sensors, and flow/return temperatures, to move from estimates to data-driven analysis.
• Winter performance under real adversity: Can this system maintain comfort through a sustained cold spell (−5°C for 7+ days)? Or would there be a cost-wellbeing trade-off?
• Optimal dispatch strategy: Should I charge the battery from cheap off-peak electricity or from solar generation? Should I export during peak-pricing windows or maximise kWh sold?

Unknown Unknowns

These are the surprises that may emerge:

• Thermal mass and fabric storage: How much does the building fabric act as thermal storage? Could I pre-heat the house during cheap-rate periods?
• Demand flexibility and comfort trade-offs: How far can behaviour shift? Could I shift 30% of heating demand to high-solar windows without compromising health or productivity?
• Grid decarbonisation feedback: As the UK grid gets cleaner (more renewables, less coal/gas), the carbon value of each kWh of ASHP electricity will change. How should this shape optimisation strategy?
• Second-order effects: Will an (PH)EV (planned for 2026) create new patterns of electricity demand that interact with heating and solar in unexpected ways?

Looking Ahead: 2026 and Beyond

The foundation is now in place. The next phase is refinement:

1. Transport electrification: An (plug-in hybrid) electric vehicle is planned for 2026. The Zappi charger is ready. Charging will raise electricity demand again, but in a schedulable way. I can time charging to solar peaks or cheap-tariff windows. This creates an interesting household energy optimisation problem.

2. Heating control sophistication: Weather-compensated flow temperature (already available in the Daikin), room-by-room zoning (via wireless thermostatic radiator valves), thermal pre-charging of the building fabric during cheap-rate periods. All reduce peak demand and smooth seasonal variation.

3. System instrumentation: Adding heat meters, outdoor temperature sensors, and API connections to enable detailed performance monitoring and feedback into the dispatch algorithm.

4. Peer learning and knowledge sharing: This data is only valuable if shared. I want to connect with other households on similar journeys, compare real-world performance, and contribute to the evidence base for UK heat pump deployment.

Conclusion

I set out to ask a simple question: Am I practising what I preach?

The answer is: better than before, and measurably so.

The structural changes are fundamental:

• Gas combustion for heating has been eliminated (Scope 1 from gas dropped 56%).
• The household became an electricity producer for the first time (1.9 MWh exported).
• Annual energy costs fell by roughly 50%.

On home energy alone, the footprint fell from 1,789.77 tCO₂e to 1,036.23 tCO₂e (a 42% reduction)using consistent 2025 emission factors. On my full footprint (all scopes), the reduction is 31%, from 3,410 to 2,352 kgCO₂/year.

But it’s not net-zero yet. Electricity imports remain substantial (3.35 MWh/year), and Scope 3 emissions from transport and flights continue. The next phase, reduction of transport emissions and continued solar/battery optimisation, will be important.

More profoundly, this transition has taught me that the gap between theory and practice is smaller than I feared. The models, the efficiency numbers, the financial arguments – they held up. An ASHP does work in a UK climate. Solar does generate usefully. The mathematics align.

But the gap isn’t zero either. There are real questions about winter resilience, network constraints, battery effectiveness, and user behaviour. These can only be answered by living the transition, not just modelling it.

The implication for others: If you have access to grants (BUS or other schemes), the economic barrier to installing a heat pump is now minimal. The carbon case is strong. The willingness to experiment and adapt is more important than perfect foresight.

I will continue reporting on this journey. Expect updates on winter performance, EV charging integration, and deeper analysis of the ASHP’s seasonal COP. The transition to net-zero household energy is underway. It’s working. But it’s not trivial, and it teaches you things no spreadsheet model ever can.