How to Conduct a Home Energy Audit — Efficiency Score & Savings
Introduction
Your home is likely your largest financial asset—and your biggest source of wasted energy. The average UK household spends over £1,500 annually on energy, yet much of this is lost through poor insulation, inefficient appliances, and air leaks. A home energy audit is the systematic process of identifying where your home is losing energy and money, providing a clear roadmap for cost-effective improvements. Learning how to conduct a home energy audit—whether as a DIY assessment or by understanding professional diagnostics—empowers you to prioritise upgrades that deliver the highest return on investment, improve comfort, and reduce your carbon footprint. This guide explains the four pillars of home efficiency, walks you through a step-by-step audit process, and offers practical strategies for turning audit findings into real-world savings.
The Four Pillars of Home Energy Efficiency
A comprehensive energy audit evaluates your home across four key areas:
1. The Building Envelope (Your Home’s Shell)
This is the barrier between your conditioned indoor space and the outside environment. Its performance is measured by:
- Insulation R-Value: Higher R-values mean better resistance to heat flow. Recommended levels:
- Loft/Attic: R-30 to R-60 (270–500mm mineral wool)
- Walls: R-13 to R-21 (cavity wall insulation or solid wall insulation)
- Floors: R-25 to R-30 (insulated suspended floors or ground floors)
- Windows and Doors:
- U-Value: Measures heat loss (lower = better). Double-glazed: U=1.2–3.0; Triple-glazed: U=0.8–1.2
- Air Leakage: Check for drafts around frames—use a candle or incense stick to detect airflow
- Air Tightness: Measured in air changes per hour (ACH). A leaky home may have 10+ ACH; a well-sealed home is below 5 ACH
2. HVAC Systems (Heating, Ventilation, Cooling)
Heating accounts for ~60% of UK home energy use. Key metrics:
- Boiler Efficiency: Modern condensing boilers are 90–94% efficient (A-rated). Older non-condensing models may be below 70% efficient.
- Heat Pump Performance: Measured by SPF (Seasonal Performance Factor). An SPF of 3.0 means 1kW of electricity delivers 3kW of heat.
- Ductwork: Leaky ducts in unconditioned spaces can waste 20–30% of heated/cooled air
3. Water Heating
Water heating uses ~15% of home energy. Efficiency is measured by:
- Energy Efficiency Rating: A-rated cylinders are most efficient
- Insulation: Hot water cylinder jackets should be ≥75mm thick
- Flow Rates: Low-flow showerheads (8–9 L/min vs. 15+ L/min) cut hot water use by 40%
4. Lighting and Appliances
This “plug load” category uses ~15–20% of home energy:
- Lighting: LEDs use 85% less energy than incandescents
- Appliances: A+ to A+++ ratings indicate efficiency (A+++ is best)
- Standby Power: “Vampire loads” from electronics can cost £50–£100/year
Step-by-Step DIY Energy Audit Process
Step 1: Gather Your Data
- Collect 12 months of energy bills to establish baseline usage
- Note your home’s age, construction type, and square footage
- List all major appliances with their age and energy ratings
Step 2: Inspect the Building Envelope
- Attic: Check insulation depth (should be ≥270mm). Look for gaps around hatches and pipes.
- Walls: Feel for cold spots in winter (indicates missing insulation). Check cavity wall insulation status.
- Windows/Doors: Close a £5 note in the frame—if you can pull it out easily, you need weatherstripping.
- Basement/Crawlspace: Ensure floor insulation is intact and pipes are insulated.
Step 3: Evaluate HVAC and Water Heating
- Boiler: Check the efficiency rating and age (replace if >15 years old)
- Thermostat: Is it programmable? Set to 19–21°C in winter, 23–25°C in summer
- Water Heater: Verify cylinder insulation and set temperature to 60°C
Step 4: Assess Lighting and Appliances
- Count incandescent/halogen bulbs (replace with LEDs)
- Check appliance energy labels—prioritise replacing G-rated with A-rated models
- Use a plug-in energy monitor to measure standby power of entertainment systems
Step 5: Calculate Your Efficiency Score
Assign points for each feature:
- Attic Insulation: 0 (none) → 10 (R-60)
- Wall Insulation: 0 (none) → 8 (solid wall insulated)
- Windows: 0 (single-glazed) → 7 (triple-glazed)
- Boiler: 0 (below 70% efficient) → 10 (A-rated condensing)
- Lighting: 0 (all incandescent) → 5 (all LED)
Score Interpretation:
- 40–50: Excellent (top 10% of UK homes)
- 30–39: Good (better than average)
- 20–29: Fair (significant savings possible)
- below 20: Poor (urgent upgrades needed)
Pro Tips & Best Practices
- Prioritise Low-Cost, High-Impact Upgrades:
- Air sealing (£20–£100, saves £100–£200/year)
- Loft insulation top-up (£200–£300, saves £150–£250/year)
- LED lighting (£50, saves £50–£100/year)
- Use Professional Tools When Needed:
- Thermal Imaging Camera: Reveals hidden insulation gaps (£50–£100 to rent)
- Blower Door Test: Quantifies air leakage (£150–£300 from energy assessors)
- Leverage Government Schemes:
- ECO4 Scheme: Free insulation for low-income households
- Boiler Upgrade Scheme: £7,500 grant for heat pumps
- 0% VAT: On insulation and heat pumps until 2027
- Calculate Payback Periods:
- Formula:
Payback = Upgrade Cost / Annual Savings - Good ROI: below 5 years (e.g., loft insulation: £250 / £200 = 1.25 years)
- Formula:
Practical Applications
- Pre-Purchase Assessment: Audit a home before buying to estimate upgrade costs
- Post-Retrofit Verification: Confirm savings after installing insulation or a heat pump
- Rental Property Management: Meet MEES (Minimum Energy Efficiency Standards) for EPC rating ≥E
- Net Zero Planning: Identify steps to reach EPC A rating by 2035 (UK target)
Practice Conducting Energy Audits
Scenario 1: The 1930s Semi-Detached House
Features:
- No cavity wall insulation
- 100mm loft insulation
- Single-glazed windows
- 20-year-old G-rated boiler
- Mix of LED and halogen lighting
Task:
- Calculate efficiency score (max 50)
- Prioritise top 3 upgrades with estimated costs/savings
- Check eligibility for ECO4 grants
Scenario 2: The 1990s New Build
Features:
- Cavity wall insulation (installed)
- 200mm loft insulation
- Double-glazed windows (U=2.8)
- 10-year-old B-rated boiler
- All LED lighting
Task:
- Calculate efficiency score
- Identify “next-level” upgrades (e.g., heat pump, solar PV)
- Estimate carbon savings from switching to renewable heating
Scenario 3: The Listed Building
Features:
- Solid stone walls (no cavity)
- Original sash windows (single-glazed)
- No loft access (vaulted ceilings)
- Oil-fired boiler (75% efficient)
Task:
- Calculate efficiency score
- Recommend non-invasive upgrades (e.g., secondary glazing, radiator reflectors)
- Discuss heritage considerations with local planning authority
Scenario 4: Post-Upgrade Verification
After installing:
- Cavity wall insulation (£500)
- Loft insulation top-up to 300mm (£300)
- A-rated boiler (£3,000)
Task:
- Recalculate efficiency score
- Compare pre/post energy bills to verify savings
- Calculate actual vs. projected payback periods
What’s the difference between a DIY and professional energy audit?
A DIY audit uses visual inspection and basic tools to identify obvious issues. A professional audit (conducted by a qualified Domestic Energy Assessor) includes:
- Blower door test to measure air tightness
- Thermal imaging to detect hidden heat loss
- Official EPC rating (required for rentals/sales)
- Detailed report with costed recommendations
How much does a professional energy audit cost?
In the UK, a basic audit costs £100–£250. This includes an EPC and basic recommendations. Advanced audits with blower door testing cost £300–£500 but provide precise quantification of energy losses.
What is an EPC and why does it matter?
An Energy Performance Certificate (EPC) rates your home’s energy efficiency from A (most efficient) to G (least efficient). It’s legally required when selling or renting a property. From 2025, rental properties must have EPC ≥C; from 2028, all homes must meet this standard.
Should I replace my windows first?
No—prioritise insulation and air sealing first. Windows are expensive (£300–£600/window) with long payback periods (10–20 years). Insulation (£250 for loft top-up) pays back in 1–2 years. Only replace windows if they’re damaged or single-glazed.
What’s the best way to insulate solid walls?
For solid wall properties (common in pre-1920s homes):
- Internal insulation: Cheaper (£40–£70/m²) but reduces room size
- External insulation: More effective (£90–£140/m²) but requires planning permission for listed buildings Both can reduce heating bills by 15–20%.
How do I find grants for energy upgrades?
Check these UK resources:
- Simple Energy Advice: Official government portal for grants
- ECO4 Scheme: For low-income households (administered by energy suppliers)
- Boiler Upgrade Scheme: £7,500 for heat pumps (apply via MCS-certified installer)
- Local Authority Flexibility: Some councils offer additional funding
Can I do an energy audit myself?
Yes—this guide provides a comprehensive DIY framework. However, for official purposes (EPC, grant applications), you’ll need a qualified Domestic Energy Assessor. Use your DIY audit to prepare questions for the professional.
How often should I audit my home?
- DIY audit: Annually (before winter)
- Professional EPC: Every 10 years (or when selling/renting)
- Post-upgrade verification: After major renovations (e.g., new heating system)
What’s the biggest energy waster in UK homes?
Poor insulation and air leaks account for 35–40% of heating losses. In a typical semi-detached house, upgrading from no insulation to recommended levels can save £250–£400/year on heating bills.