Does Your EPC Lie? The Gaps in Accuracy You Should Know

You’ve received your EPC (Energy Performance Certificate). It gives your home a letter grade from A to G. You assume it reflects your property’s actual energy performance—right?

Not necessarily.
EPCs are notoriously imperfect, and in some cases, the certificate can be misleading or outright inaccurate. Whether you’re buying, selling, renting, or upgrading a home, it’s crucial to understand where EPC assessments fall short—and how those gaps can affect your decisions.

1. Assumptions Over Actual Performance

The most fundamental flaw in EPC assessments is that they don’t measure real energy use.

• EPCs are based on the Standard Assessment Procedure (SAP) or Reduced SAP (RdSAP) for existing homes.

• These models use assumptions, not measurements.

• Your actual usage, behaviours, or smart upgrades may not be reflected at all.

👉 The result: Two homes with vastly different energy bills could receive identical EPC scores.

2. Missing or Poor Documentation Can Hurt Your Score

EPC assessors can only rate what they can see or verify with proof. If your installer never gave you:

• Loft insulation certificates

• Solar PV installation documents

• Air tightness test results

Then your EPC may default to conservative values—even if your home is highly efficient.

👉 The result: Homes with unrecorded improvements get artificially low ratings.

3. Smart Tech Often Gets Ignored

Have you installed:

• A smart thermostat like Nest or Hive?

• Zoned heating controls?

• Battery storage for your solar panels?

Unfortunately, these often don’t register in the EPC software or are weighted minimally. The system still favours conventional metrics like boiler efficiency and wall insulation.

👉 The result: Your innovative systems may have little to no impact on your EPC.

4. Fuel Type Bias Skews Scores

EPCs assign energy scores partly based on the carbon intensity and cost of the fuel, not just efficiency.

• Electric heating, even with renewables, is penalised due to outdated grid assumptions.

• Gas heating, though less eco-friendly, may score better.

👉 The result: A home with a heat pump may score worse than one with a gas boiler, even if it’s greener.

5. Room Orientation and Solar Gain Are Poorly Calculated

EPCs don’t always accurately account for:

• South-facing windows that reduce heating demand

• Overhangs and shading that prevent overheating

• Thermal mass and passive solar design

👉 The result: Architectural features that lower real energy use might be ignored or undervalued.

6. Older EPCs May Be Way Off

If your EPC is more than 5–10 years old:

• It likely uses outdated SAP software

• It doesn’t reflect upgrades since then

• Energy prices, carbon factors, and efficiency benchmarks have all changed

👉 The result: You may be relying on obsolete data that doesn’t match your home today.

So, Does Your EPC Lie?

Not intentionally—but it often tells a simplified, outdated, or incomplete story. EPCs were never designed to be perfect. They’re a broad estimation tool, not a forensic energy audit.

But that doesn’t mean you’re powerless.

What You Can Do:

✅ Always provide evidence: Give your assessor all documentation for insulation, systems, and upgrades.
✅ Use a qualified, experienced assessor who understands the nuances of SAP modelling.
✅ Supplement your EPC with other reports (like blower door tests or thermal imaging) if you’re investing in retrofits.
✅ Treat your EPC as a baseline, not a verdict.

Final Thought:
Your EPC may not be lying—but it might not be telling the whole truth either. In a world moving toward net-zero housing and greener living, understanding the limits of your energy certificate is the first step toward making smarter, more accurate decisions.

📍 Final Takeaway