Home Energy Audit: What to Expect (And Why You Should Get One)
A home energy audit is the starting point for almost every meaningful energy efficiency improvement. Before you spend a dollar on insulation, windows, or HVAC upgrades, an audit tells you exactly where your home is losing energy and which fixes deliver the best return. Here’s what auditors actually do, what they find, and what it costs.
What Is a Home Energy Audit?
A home energy audit is a systematic assessment of how much energy your home uses and where it’s being wasted. A trained auditor inspects your home’s envelope (walls, roof, windows, doors), mechanical systems (HVAC, water heater, appliances), and air sealing to identify inefficiencies.
There are three levels of audits:
Level 1 – Walk-through assessment Basic visual inspection. Auditor checks visible insulation, appliances, and reviews utility bills. Takes 1–2 hours. Low cost or free through some utilities. Limited diagnostic value.
Level 2 – Diagnostic audit (most common) Full inspection plus specialized equipment — blower door test, infrared camera, combustion safety testing. Takes 2–4 hours. This is what most homeowners need. Costs $200–$600.
Level 3 – Investment-grade audit Detailed engineering analysis for major building retrofits or commercial properties. Rarely needed for single-family homes.
Most homeowners need a Level 2 audit. The rest of this guide covers what to expect from a full diagnostic audit.
Who Performs Home Energy Audits?
Look for auditors certified by:
- BPI (Building Performance Institute) — the gold standard for residential auditors
- RESNET (Residential Energy Services Network) — certifies HERS raters
- ENERGY STAR — some utility programs use ENERGY STAR-certified auditors
Many electric and gas utilities offer free or subsidized audits — often $0–$100 after rebate. Check your utility’s website or call customer service before paying full price. Some states also offer income-qualified programs with free audits and no-cost weatherization.
The Blower Door Test: The Core of Any Good Audit
The blower door test is the most important diagnostic tool in a residential energy audit. Here’s exactly how it works:
- The auditor mounts a powerful fan in an exterior door frame (usually the front door)
- The fan depressurizes the house to a standard 50 Pascals below outdoor pressure
- A manometer measures airflow required to maintain that pressure — indicating how leaky the building envelope is
What the numbers mean:
| ACH50 (Air Changes per Hour at 50 Pa) | Building Tightness |
|---|---|
| Less than 1.0 | Very tight (newer high-performance homes) |
| 1.0–3.0 | Tight (post-2000 construction) |
| 3.0–7.0 | Average (1980s–1990s construction) |
| 7.0–15.0 | Leaky (pre-1980 construction) |
| 15.0+ | Very leaky (older unimproved homes) |
The average U.S. home built before 1980 tests around ACH50 10–15. Modern energy codes target ACH50 3.0 or lower. Even modest air sealing in a leaky home can cut heating/cooling costs 15–25%.
While the blower door runs, the auditor uses smoke pencils or fog to find exactly where air is entering or escaping — around electrical outlets, baseboards, attic hatches, recessed lights, and window frames.
Infrared (Thermal) Camera Scanning
An infrared camera detects surface temperature differences that indicate missing insulation, air leaks, moisture problems, and thermal bridging through framing.
What the auditor looks for:
- Cold spots on ceilings/walls in winter = missing or damaged insulation
- Warm spots on ceilings in summer = heat radiating through thin spots
- Air infiltration patterns = cold air streaking in from framing gaps, outlets, windows
- Moisture intrusion = wet areas show as temperature anomalies before visible staining appears
- Thermal bridging = wall studs and joists appear clearly because wood conducts heat better than insulation
Infrared scanning works best during significant temperature difference between inside and outside (at least 15–20°F difference). Many auditors won’t bring the camera in mild weather because results are less reliable.
What homeowners commonly see:
“Our auditor found that our entire south wall had almost no insulation in the top third — the blown-in had settled over 30 years and nobody knew. The infrared scan made it obvious in seconds.”
Combustion Safety Testing
If your home has gas appliances (furnace, water heater, stove, fireplace), a good auditor tests for combustion safety:
- Carbon monoxide (CO) spillage from furnaces and water heaters
- Backdrafting — combustion gases flowing back into living space instead of exhausting outside
- Gas pressure and burner condition — basic check for obvious issues
- Flue integrity — visual inspection of venting
This is especially important when improving air sealing. A very tight home can starve combustion appliances of makeup air, increasing backdraft risk. A qualified auditor tests before and after air sealing to ensure safety.
What Auditors Typically Find
Based on national data from thousands of home audits, the most common findings in older homes:
Air Leakage (Almost Universal)
- Top plates (attic/wall connection) — #1 source of air leakage
- Recessed lighting cans penetrating the ceiling
- Attic hatch (often uninsulated and unweatherstripped)
- Rim joists (basement/foundation wall intersection)
- Electrical outlets and switch plates on exterior walls
- Plumbing penetrations
Insulation Deficiencies
- Under-insulated attic floor (below R-30 in most homes)
- No rim joist insulation (major heat loss in cold climates)
- Poorly installed or compressed wall insulation
- Missing insulation above garage (common)
HVAC Issues
- Leaky duct systems (average home loses 20–30% of conditioned air through duct leaks)
- Oversized or undersized HVAC equipment
- Clogged filters reducing airflow
- Older equipment running well below rated efficiency
Miscellaneous
- Inefficient water heater (often 10–15+ years old)
- Uninsulated hot water pipes
- Excessive phantom loads from electronics
- Single-pane or inefficient windows
Typical Audit Findings: Cost vs. Savings
| Finding | Fix Cost (DIY) | Fix Cost (Pro) | Annual Savings |
|---|---|---|---|
| Air sealing attic top plates | $50–$150 | $300–$800 | $100–$300 |
| Attic insulation upgrade | $500–$1,200 | $1,500–$3,500 | $150–$500 |
| Rim joist insulation | $100–$300 | $400–$900 | $100–$250 |
| Duct sealing | $50–$150 | $300–$800 | $100–$300 |
| HVAC tune-up | N/A | $75–$150 | $50–$150 |
| Hot water pipe insulation | $20–$50 | $100–$200 | $30–$60 |
Savings estimates vary widely by home size, climate, energy prices, and current conditions.
How Long Does an Audit Take?
A thorough Level 2 audit of a 2,000 sq ft home takes 2.5–4 hours. Larger homes or more complex problems take longer.
Typical timeline:
- 15–30 min: Review utility bills, interview homeowner about comfort complaints
- 30–45 min: Walk-through inspection of attic, basement, crawl space, living areas
- 45–60 min: Blower door test and simultaneous air sealing investigation
- 30–45 min: Infrared scan (if temperature differential allows)
- 20–30 min: Combustion safety testing (if applicable)
- 15–30 min: Review findings with homeowner
After the audit: You’ll receive a written report, typically within 3–5 business days, listing findings prioritized by impact-to-cost ratio. Quality reports include estimated project costs, projected savings, and available incentives.
What Does a Home Energy Audit Cost?
| Audit Type | Typical Cost | Who Offers It |
|---|---|---|
| Utility-sponsored free audit | $0 | Electric/gas utilities (limited availability) |
| Utility-sponsored subsidized audit | $50–$150 | Many utilities nationwide |
| Full independent diagnostic audit | $200–$400 | BPI-certified contractors |
| Premium audit with full report | $400–$600 | Larger energy consulting firms |
Cost factors:
- Home size (larger = more time)
- Geographic region (labor rates vary)
- Services included (infrared, combustion testing, duct blaster)
- Whether auditor also performs the work (some offer “audit plus installation” packages)
Is an Energy Audit Worth It?
Yes — with caveats.
Worth it when:
- Your home is older than 15–20 years and hasn’t been weatherized
- You have high utility bills relative to your area
- You have comfort complaints (cold rooms, drafty hallways, temperature swings)
- You’re planning major renovations and want to sequence energy work correctly
- You want to maximize ROI before investing in solar or heat pumps
Less valuable when:
- Your home was built post-2010 and is already well-insulated
- You’ve had recent weatherization work done
- You’re only renting and can’t authorize improvements
Most homeowners who complete a full diagnostic audit and implement the top recommendations recover the audit cost in energy savings within 1–2 years — before any of the improvement payback is counted.
Frequently Asked Questions
Q: What should I do to prepare for an energy audit? Clear access to the attic hatch, furnace/water heater, and electrical panel. Have 12 months of utility bills available. Write down comfort complaints (cold rooms, drafty spots, high bills in specific months).
Q: Does the auditor also do the work? Some do, some don’t. Independent auditors who don’t perform work have no incentive to oversell recommendations. Contractor-auditors can offer “audit + remediation” packages but shop the work. Both models are legitimate.
Q: What if the audit finds asbestos or mold? The auditor will note it in the report and recommend remediation before any insulation or air sealing work. They won’t touch it.
Q: Will my utility give me a rebate after the audit? Many utilities offer rebates for specific improvements — not the audit itself. Your auditor should know local incentive programs and which improvements qualify. Always ask before starting work.
Q: Can I do my own energy audit? You can do a basic walk-through, but the blower door test and infrared scan require specialized equipment. DIY apps and checklists miss what professional equipment finds. A professional audit is worth the cost.
Q: How often should I get an energy audit? Once every 10–15 years, or any time you complete major work (new roof, HVAC replacement, significant renovation) that changes the building envelope.
Finding a Qualified Energy Auditor Near You
Finding a certified, experienced auditor is the most important step. Look for BPI Building Analyst certification as the minimum. Ask about their equipment, what’s included in the report, and whether they’re familiar with local utility incentive programs.
A local auditor knows your climate zone, building stock, and which utilities offer what programs — knowledge that can save hundreds of dollars in rebates and avoid fixes that don’t make sense for your region.