Your EPC rating isn’t determined only by big upgrades like new boilers or insulation. Often, it’s the hidden issues—small, silent, easily overlooked inefficiencies—that drag your score down without you even realising it.

These “EPC killers” can quietly knock your energy rating from a C to a D, or from a D to an E, costing you compliance, rental opportunities, and long-term energy savings.

Here are the most common hidden EPC killers and how to fix them before your assessment.

1. Invisible Draughts You Don’t Notice Daily

You may not feel them, but your assessor will.

Hidden draught sources include:

  • Gaps behind skirting boards

  • Unsealed floorboards

  • Chimneys without a draught excluder

  • Lofts with unsealed access hatches

Even small air leaks lead to huge heat loss and will instantly lower your EPC rating.

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2. Poorly Insulated Hot-Water Pipes

Most homeowners insulate their hot-water cylinder but forget the pipes.

Unlagged pipes cause:

  • Rapid heat loss

  • Higher water-heating costs

  • Lower EPC scores due to inefficiency

Pipe insulation is cheap, quick, and one of the most effective EPC quick wins.

3. Old or Hidden Ventilation Issues

Bathrooms and kitchens often have extractor fans that:

  • Don’t work

  • Are too weak

  • Are clogged with dust

  • Are incorrectly vented

Poor ventilation leads to damp, mould, and reduced thermal performance—all EPC red flags.

4. Degraded Loft Insulation You Can’t See

Even if your loft was insulated years ago, it may no longer be effective.

EPC assessors frequently find:

  • Compacted insulation

  • Damp or mouldy insulation

  • Insulation disturbed by pests or contractors

If the thickness isn’t consistently around 270mm, expect points to drop.

5. Outdated Room Thermostats & Controls

Many homes still use:

  • Basic dial thermostats

  • Outdated timers

  • Radiators without TRVs

Even if your boiler is efficient, poor controls kill your EPC score because the system can’t operate efficiently.

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6. Poorly Performing Double Glazing

Double glazing isn’t always efficient. Assessors look for:

  • Condensation between panes

  • Warped or weathered frames

  • Broken seals

  • Cold air leaks

Damaged double glazing performs like single glazing—and the EPC software will treat it that way.

7. Hidden Solid Walls Without Insulation

Solid walls often look fine from the inside, but if they’re uninsulated, they cause:

  • Massive heat loss

  • Poor thermal retention

  • A significantly lower EPC band

Without documentation or visible proof, assessors must assume no insulation.

8. Chimneys, Fireplaces & Flues

Even unused chimneys create constant heat loss unless blocked or sealed.

Hidden EPC killers include:

  • Open flues

  • Uncovered fireplaces

  • Dampers that don’t close properly

Simple chimney balloons or draught excluders make a big difference.

9. Ageing Hot-Water Cylinders

Some homeowners don’t realise their cylinder:

  • Is non-foam lagged

  • Lacks proper insulation

  • Has inefficient immersion heaters

A cylinder jacket alone can increase your EPC score.

10. Missing Documentation for Upgrades

One of the biggest EPC killers isn’t physical—it’s paperwork.

Without proof of:

  • Loft insulation

  • Wall insulation

  • Boiler installation

  • Window upgrades

…the assessor must assume the lowest possible efficiency value.

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How to Protect Your EPC Rating

To avoid these hidden EPC killers:

  • Inspect your insulation

  • Seal gaps and draughts

  • Update heating controls

  • Check ventilation systems

  • Gather documentation early

For homeowners, landlords, and sellers preparing for an EPC, choosing the right assessor makes the biggest difference.

Email :info@epcrate.co.uk

Phone:020 34884142