Installing a low-carbon heating system might seem like a guaranteed ticket to a high Energy Performance Certificate (EPC) score. But the reality is more nuanced.
Many UK property owners and landlords have switched to heat pumps, solar PV, or biomass boilers with the hope of dramatically boosting their EPC rating. Yet some are surprised when the gain is only one band—or none at all.
So, why don’t all low-carbon upgrades deliver big EPC results? Let’s explore what’s really going on under the EPC hood.
🔍 How EPC Ratings Work: The SAP Core
EPC ratings for residential buildings are calculated using the Standard Assessment Procedure (SAP). It’s a model that simulates the building’s energy use based on:
Heat loss through walls, roof, windows, etc.
Heating system efficiency
Fuel type and emissions
Renewable energy generation
Hot water and lighting performance
📌 Learn more about EPC methodology
While SAP does recognise low-carbon systems, it still weighs overall energy demand and cost to run more heavily than just emissions reduction.
🌀 Why Some Low-Carbon Systems Don’t Deliver Big EPC Leaps
1. Electricity Is Expensive
Even if your heat pump is 300% efficient, EPC models factor in fuel costs, and electricity remains more expensive than gas in the UK.
So your heat pump may reduce emissions—but not enough to dramatically lower running costs, which EPCs still prioritise.
2. No Gains Without Fabric Upgrades
If your property has poor insulation, leaky windows, or no draft-proofing, even the most efficient system can’t shine.
EPCs reward whole-system performance—so a heat pump in a draughty Victorian terrace may underperform in SAP modelling.
📅 Get a building fabric check before installing new tech
3. Some Systems Are Penalised in the Model
Biomass boilers score well on emissions but may be downgraded due to manual feeding requirements or assumptions about user behaviour.
Solar PV only scores well if it’s big enough to meaningfully offset usage—and it doesn’t always count toward heating efficiency unless coupled with smart storage.
💡 Realistic EPC Uplifts by Technology
| Low-Carbon Upgrade | Typical EPC Band Gain | Notes |
|---|---|---|
| Air Source Heat Pump | +1 band (avg.) | Better with high insulation |
| Solar PV (2–4 kW) | +0.5 to +1 band | Depends on roof orientation and storage |
| Biomass Boiler | +0.5 to +1 band | Manual operation reduces score in some cases |
| Hybrid Heating System | +1 band (with control logic) | Stronger if paired with insulation |
| Ground Source Heat Pump | +1–2 bands (rare) | High upfront cost, best for large homes |
⚠️ These are general trends—your specific results may vary based on building fabric, size, and assessor interpretation.
🧮 EPC Is About Cost Efficiency—Not Just Carbon
SAP is still rooted in energy cost per square metre, not just carbon savings. That’s why an efficient gas combi boiler might outscore a low-use electric system, especially in well-insulated flats.
Until EPC models are fully reformed to align with net-zero goals (expected in the next SAP version), you might not see the radical score bump you expect from low-carbon tech alone.
🛠️ Want Bigger Gains? Combine Systems with Insulation
To truly maximise EPC impact:
Upgrade loft and wall insulation first
Then add smart controls (thermostats, TRVs)
Finish with low-carbon heating or solar PV
This layered approach ensures SAP sees both emissions reduction and cost savings.
🔗 Speak with an EPC assessor before committing to upgrades
🧭 Final Thoughts: Choose Systems That Work With the Model
Low-carbon systems are still worth it—from a sustainability and future-proofing standpoint. But if your primary goal is an EPC uplift, you’ll need to:
Understand how SAP calculates performance
Fix insulation and controls first
Document every upgrade thoroughly
And always work with a local, knowledgeable EPC assessor in London who understands how to capture those benefits in the final report.
💬 Still unsure if your system will deliver the EPC boost you expect?
📞 Get expert EPC guidance today
