Why Your EPC Rating Doesn’t Always Match Your Monthly Energy Costs

It’s a common complaint in 2025:

“My house has a C-rated EPC… but my gas and electric bills are sky-high!”

So what’s going on? If the Energy Performance Certificate is supposed to reflect energy efficiency, why doesn’t it align with real-world spending?

The truth is: EPCs don’t tell the whole story—and they’re not designed to.

🔍 EPC: A Predictive Model, Not a Personalised Report

Energy Performance Certificates are based on a Standard Assessment Procedure (RdSAP). This means they assess potential energy use under typical conditions.

They assume:

  • Average occupancy

  • Standard heating hours

  • Standard thermostat settings

  • No unusually high appliance use

So unless you live like a textbook homeowner, your usage will differ.

💸 7 Key Reasons Why Your Bills Don’t Match Your EPC

1. User Behaviour Changes Everything

You could have a B-rated home, but if:

  • You run the heating 24/7

  • You take long daily hot showers

  • You work from home with multiple devices on all day

…your bills will be much higher than predicted.

✅ EPC = potential
❌ EPC ≠ personalised usage

2. Tariffs & Suppliers Matter

Two neighbours with the same rating can pay wildly different amounts based on:

  • Their energy provider

  • Whether they’re on a fixed or variable tariff

  • Whether they use time-of-use tariffs (like Economy 7)

EPCs don’t consider unit rates or standing charges—yet these directly impact bills.

3. Actual Weather vs. Assumed Climate

EPCs use regional weather averages. But if you live in a particularly cold, exposed, or wind-prone area—even within London—you may consume more energy for heating than the EPC suggests.

4. Appliance Use Is Ignored

EPCs do not factor in:

  • TVs, gaming consoles, and desktops

  • Electric vehicles charging at home

  • Washing machine and dryer frequency

  • Smart gadgets running 24/7

So even a highly efficient home can have high actual usage if it’s filled with power-hungry devices.

5. Ventilation, Draughts & Habits

EPCs assume:

  • A standard level of airtightness

  • Normal ventilation (not constant open windows)

  • Minimal heat loss through open doors or flues

Real households often leave extractor fans on, dry clothes indoors, or have old chimneys left unsealed—all not captured in the certificate.

6. Upgrades After the Assessment

If your EPC is 3–5 years old, it may no longer reflect your current setup. You might’ve:

  • Changed boilers

  • Replaced windows

  • Switched heating sources

But if you didn’t update the EPC, your rating is outdated, even if your bills reflect the improvements.

7. Assessor Assumptions & Evidence Gaps

EPCs often default to conservative estimates if the assessor can’t find proof. For example:

  • No visible insulation = assume none

  • No boiler datasheet = assume lower efficiency

That means your EPC might underrate your home, even if your energy use tells a better story.

🔧 What Can You Do About It?

  • ✅ Get an updated EPC if you’ve made energy upgrades

  • ✅ Switch to a more cost-efficient tariff

  • ✅ Monitor your actual usage with a smart meter

  • ✅ Improve insulation and airtightness to reduce waste

  • ✅ Book a knowledgeable assessor who takes time to collect evidence

🧭 Need a Realistic Energy Picture?

At EPCRate London, we don’t stop at issuing a certificate. We help you:

Final Word

Your EPC is a snapshot of potential, not a crystal ball for your bills. For property owners, landlords, and tenants in London, understanding this gap can save confusion—and cash.

Want EPCs explained with clarity, not jargon? You’re in the right place.