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Home Energy Efficiency: Energy Retrofit Case Studies

mathieulafargue
June 28, 2025

ENERGY RETROFIT CASE STUDY 1: Thornton Road, London SW12

The £3,496 mistake: How right-sizing an ASHP avoided overspend, boosted ROI, and extended system life

The energy retrofit challenge:

When a landlord bought a Victorian property in SW12, it came with the usual suspects: a failing gas boiler, cold draughts, partial loft insulation, and an EPC rating of E (EER 50). A heating contractor, acting on rules of thumb, quoted for a 12kW ASHP—with no room-by-room heat loss calculations.

That oversized system would’ve cost £3,500 more to install, run inefficiently, and likely failed 3–6 years earlier than necessary.

That’s a serious error.

The problem with oversizing air source heat pumps

Oversized heat pumps are everywhere in the UK retrofit market—and they’re costing landlords tens of thousands. Here’s why:

🔻 Minimum turndown ratio: Most ASHPs can only modulate down to 25–30% of their capacity. That means a 12kW unit rarely runs below 3–4kW—yet most UK homes need less than 2kW for 70% of the year.

🔁 Inefficient cycling: When the heat pump’s output exceeds demand, it short-cycles—turning on and off constantly. This creates:

Wasted compressor energy

Faster wear-and-tear

Inefficient performance

🔧 Shorter lifespan: Field data shows oversized units often fail 3–6 years earlier due to compressor fatigue and icing issues.

💰 Unnecessary costs:

+£3,496 in extra equipment and install cost

+£28/month in added standing consumption

+£125/year in servicing and performance penalties

The Ivynest fix: Start with fabric, design to demand

Before we specified any heating system, we used SAP10-based heat loss modelling to quantify the real thermal demand. Then we took a whole-house approach:

Installed 300mm rockwool loft insulation

Upgraded to 1.4 W/m²K U-value sash windows

Applied internal wall insulation in upstairs bedrooms

Added draft-proofing around all floor voids and eaves

Result? We cut peak heating demand from 10.2kW to just 6.8kW.

Then, The Right-Sized System

We specified a 7kW Samsung EHS monobloc ASHP using R290 refrigerant — for three key reasons:

High COP at high temps
R290 offers excellent performance even at 55–65°C, making it ideal for legacy radiator systems.

Typical COP: 3.3–3.5 at 55°C, vs. 2.4–2.8 with R32

Lower GWP
R290 has a Global Warming Potential of just 3 — 700× less than R410a, aligning with decarbonisation goals.

Simplified compliance
Samsung’s MCS-accredited monobloc units are compact, quiet, and perfect for small UK gardens.

System Optimisation: No Buffer, Just Smart Volume

Instead of a large buffer tank (which introduces thermal lag and cycling inefficiencies), we used a:

✅ 30L low-loss volumiser
→ Reduces system inertia
→ Improves flow temp responsiveness
→ Maintains COP by avoiding unnecessary standby losses

Paired with our weather compensation strategy and smart heat curve control, the system delivered steady-state efficiency with low cycling rates.

Outcome

Metric	Before	After
EPC Rating	E (EER 50 / EIR 54)	B (EER 87 / EIR 88)
Energy Use	~17,400 kWh/year	~6,950 kWh/year
Heating Install Cost	£10,845 (12kW)	£7,349 (7kW)
Annual Bills	£2,400	£840
CO₂ Emissions	4.3 tonnes/year	1.1 tonnes/year
Property Value	£765,000	£825,000 (Foxtons reval)

📈 ROI uplift? ~£60,000 added to the asset.

Why it worked?

✅ Right-sizing the ASHP to the real demand
✅ Upfront saving: £3,496 on equipment + install
✅ Lower bills: ~£130/month saved
✅ Avoided early failure from oversizing
✅ Extended lifespan by 3–5 years
✅ Took full advantage of £7,000 BUS grant

Don’t pay for more kilowatts than you need.
Oversizing isn’t safer. It’s just waste.

👉 Start your Free Retrofit Plan Now
Real EPC-based analysis. AI-powered. Engineer approved.

ENERGY RETROFIT CASE STUDY 2: 87 Leek Road, Buxton SK17

How smart battery pairing saved Emma £924/year on her retrofit—and what her assessor got wrong

Emma thought she did everything right. She hired a certified retrofit assessor. She got a plan that looked textbook:

✅ Solar PV system

✅ Immersion diverter

✅ ASHP installation

But when the first bills came in, she panicked. Despite her upgrade, her electricity bills were £87/month higher than before.

Why diverters often fail in modern retrofits

Emma’s diverter sent all surplus solar power to a direct immersion heater (COP = 1)—basically a hot rod in a tank.

That sounds efficient, but here’s the truth:

1 kWh solar in = 1 kWh heat out

But immersion heating is the least efficient use of electricity

Worse, her setup didn’t store excess energy for use later

She missed off-peak tariffs entirely

The Ivynest Intervention

Our engineers rebuilt the system with smarter sequencing:

🔋 Added a 4.8kWh battery for solar storage

🔄 Fed battery output directly into a 5kW Samsung ASHP

🌞 Used Ivynest’s HEMS to optimise charging from off-peak grid + solar

🔧 Refined heating schedule to match room-by-room loads

📊 Tracked savings in real time via NestIO dashboard

The key?
Emma’s ASHP had a COP ≈ 3.9, meaning:

🔌 1 kWh stored = 3.9 kWh of delivered heat
That’s 3.9x more efficient than her old diverter.

Technical Edge

COP optimisation through SAP10

ASHP inverter matched to Emma’s real-time load curve

Minimum turndown kept at 1.6kW, well under low-demand thresholds

Thermal storage strategy tuned for tariff windows (e.g. Octopus Go)

Emma now has a system that works with the grid, not against it—and she’s saving hundreds annually without even noticing.

✅ Avoid retrofit regret.
✅ Don’t follow textbook checklists.
✅ Follow the data.

🔎 Generate your Free Retrofit Plan
No sales. No fluff. Just smart, performance-based planning.

🏁 Conclusion: Why Ivynest is the Energy Retrofit Partner That Gets It Right

Whether it’s preventing costly oversizing in London or turning a poor retrofit around in Buxton, these case studies show one thing clearly:

Smart retrofits aren’t about checking boxes—they’re about sequencing, precision, and system thinking.

At Ivynest, we don’t just design to EPC targets. We design for real-world performance, cost efficiency, and long-term reliability. That means:

Accurate SAP10-based heat loss modelling—no more guesswork or rule-of-thumb sizing
Engineer-led design—not templates from 4-day training courses
Detailed, MCS-compliant technical packs and tenders—ready for grant applications, procurement, and smooth delivery
Upfront ROI analysis—based on energy pricing, system specs, and CAPEX
Access to funding—with built-in support for BUS, ECO4, and tailored green finance
Delivery-ready outputs—used by contractors, lenders, and landlords alike