Most homes waste 30–40% of their heating energy through gaps, poorly insulated surfaces, and ageing appliances nobody has properly assessed since they were installed. A home energy audit changes that — it maps where your money is escaping and gives you a prioritised list of fixes. This home energy audit guide explains exactly what happens during an assessment, what it costs, how to prepare, and what to do with the results.

What Is a Home Energy Audit?

A home energy audit — sometimes called an energy assessment or home performance assessment — is a systematic evaluation of how your home uses and loses energy. A qualified assessor identifies inefficiencies and recommends improvements ranked by cost-effectiveness.

A thorough professional audit covers the building fabric (walls, floors, ceilings, windows, and doors), air tightness, your heating and hot water systems, lighting and appliances, and whether renewables like solar panels or a heat pump would actually work for your property.

The output is a detailed report with projected savings for each recommended measure — which makes it much easier to prioritise upgrades against your budget rather than guessing.

The Blower Door Test

The blower door test is the most technically revealing part of a professional audit. An assessor seals your exterior doors and installs a large, calibrated fan in one doorway. When it runs, it depressurises the house and air rushes in through every gap, crack, and unsealed penetration.

The result is an air leakage rate expressed in air changes per hour at 50 pascals of pressure (ACH50). For context: new Passivhaus builds achieve under 0.6 ACH50; a good modern build runs 3–5 ACH50; a typical 1970s–1990s UK house comes in at 8–15 ACH50; and a draughty Victorian property can hit 15–25+.

Every ACH above the design target represents warm air — and money — escaping. The blower door test makes this concrete and measurable rather than a feeling.

Thermal Imaging: Seeing What You Can’t See

Thermal (infrared) cameras reveal temperature differences on surfaces invisible to the naked eye. During an audit, the assessor photographs walls, ceilings, floors, and around windows and doors — ideally when there’s a significant temperature difference between inside and outside (at least 10°C, so a cold winter morning is ideal).

What thermal imaging finds: missing or insufficient insulation showing up as cold patches on walls or ceilings; thermal bridges where structural elements conduct cold into the building; hidden damp where evaporative cooling creates cold signatures; and air infiltration paths around skirting boards, electrical fittings, and loft hatches.

A single thermal image of an uninsulated cavity wall junction is often more persuasive than any calculation — it’s hard to argue with a vivid cold patch on a wall you thought was insulated.

Appliance and Systems Checks

Beyond the building fabric, a good auditor reviews your boiler’s efficiency (a pre-2005 boiler typically runs at 65–75% efficiency; a modern condensing combi at 92–94%), your heating controls and zoning, hot water cylinder insulation, lighting (proportion of LED versus remaining halogens), and standby loads — some older TVs and game consoles draw 10–30W continuously, which adds up across a whole household.

DIY vs Professional Energy Audit

DIY energy audit (free–£50): You can get a useful picture of your home’s energy profile without spending much. Review your EPC (Energy Performance Certificate) at gov.uk/find-energy-certificate for any home sold or let since 2008. Walk around on a cold, windy day with a lit incense stick — draught paths become visible at window edges, skirting boards, and floor hatches. Check your bills against the typical consumption figures on your EPC.

Professional audit (£150–£500): Professional audits include instrumented testing that can’t be replicated at home:

  • Basic EPC + report: £150–200 (mainly for compliance purposes, limited detail)
  • Mid-range home performance assessment: £250–350 (blower door, thermal imaging, systems review, prioritised report)
  • Comprehensive audit: £400–500 (full thermal imaging, detailed modelling, whole-house upgrade pathway)

The comprehensive tier is worth it if you’re planning significant renovation work and want to sequence measures correctly — for example, knowing whether to insulate before or after fitting a heat pump.

How to Prepare for Your Audit

Getting the most from your assessment takes a small amount of preparation. Gather 12 months of gas and electricity bills — they give the auditor baseline consumption data. Locate your boiler service records and any previous insulation work. Clear access to the loft hatch, underfloor access panels, airing cupboard, and meter cupboard. If possible, book in winter when outdoor temperatures are low and thermal imaging is most revealing. And make a list of known issues — cold rooms, condensation on windows, damp patches — so the auditor can focus on what matters.

What to Do With the Results

A good audit report prioritises recommendations by payback period and disruption level. A typical sequence:

Quick wins (£0–200, immediate payback): draught-proofing, hot water cylinder insulation jacket, smart thermostat programming, switching remaining halogens to LED.

Medium investment (£500–3,000, 3–8 year payback): loft insulation top-up, cavity wall insulation, heating controls upgrade.

Major measures (£3,000–20,000, 7–15 year payback): external or internal wall insulation, triple glazing, new boiler or heat pump.

Renewables: once the fabric is improved, solar panels or a heat pump operate far more efficiently — don’t put the cart before the horse.

Government Schemes to Fund Improvements

Several schemes can offset upgrade costs following an audit:

  • Great British Insulation Scheme: free or subsidised cavity and loft insulation for lower EPC-rated homes
  • ECO4: fully funded insulation and heating upgrades for households on qualifying benefits
  • Boiler Upgrade Scheme: £7,500 grant toward an air source heat pump
  • 0% VAT on insulation and renewables: effective since 2022

An independent auditor — not tied to any particular product or installer — is best placed to tell you which schemes you qualify for. The upfront cost of a comprehensive audit frequently pays back many times over in grant funding it helps you access. That’s a pretty good return on £400–500.