An energy audit is a systematic inspection of a home or building to identify where energy is being wasted and what changes would reduce utility bills. It covers everything from air leaks and insulation gaps to heating system efficiency and appliance energy use. A professional audit typically costs a few hundred dollars, though a federal tax credit currently covers up to $150 of that cost. Depending on what the audit finds, acting on its recommendations can cut energy bills by roughly 12 to 21% for insulation upgrades alone, with additional savings from other improvements.
What Happens During an Energy Audit
A professional energy audit combines a physical walkthrough with diagnostic testing. The auditor examines your home’s building envelope (walls, attic, windows, doors, and foundation) for air leaks, insulation problems, and moisture issues. They also evaluate your heating and cooling systems, water heater, ductwork, lighting, and major appliances.
Two diagnostic tools do most of the heavy lifting. The first is a blower door test: a powerful fan is temporarily mounted in an exterior doorway and pulls air out of the house, lowering the indoor air pressure. Higher-pressure outdoor air then rushes in through every unsealed gap, crack, and opening, letting the auditor measure your home’s total air leakage rate. That number gets recorded digitally and compared against benchmarks for your home’s size and climate zone.
The second key tool is a thermal imaging camera. While the blower door is running, the auditor scans walls, ceilings, and floors with an infrared camera that reveals temperature differences invisible to the naked eye. Cold spots behind a wall indicate missing insulation. Warm streaks around a window frame show air infiltration. The auditor may also use a nontoxic smoke pencil, holding it near suspected leak points to watch the smoke trail get pulled toward gaps.
At the end, you receive a written report ranking the recommended improvements by cost-effectiveness. The report details estimated savings for each upgrade and often prioritizes quick wins (like air sealing and attic insulation) over larger investments (like window replacement).
Safety Testing for Gas Appliances
If your home has natural-draft appliances like a gas furnace, boiler, or water heater, a proper audit includes combustion safety testing. The auditor measures carbon monoxide levels in the appliance zone and checks for natural gas leaks before turning anything on. With the equipment running, they verify that exhaust gases are drafting correctly up the flue rather than spilling into your living space. This is done with a smoke pencil held near the draft hood: if the smoke gets pulled into the flue, the system is drafting properly. If it blows back into the room, there’s a venting problem that poses a health risk.
This testing matters because tightening a home’s air envelope (which is often the top audit recommendation) can change how combustion appliances get their air supply. A well-sealed home needs adequate combustion air pathways, or you risk carbon monoxide backdrafting into living spaces.
Three Levels of Commercial Audits
For commercial buildings, the industry standard (ASHRAE Standard 211) defines three audit levels of increasing depth and cost:
- Level 1, Walk-Through Survey: A brief on-site assessment that identifies low-cost and no-cost savings opportunities. This is a screening tool, not a deep analysis.
- Level 2, Energy Survey and Analysis: A more detailed evaluation with energy use breakdowns, diagnostic testing, and financial analysis of recommended upgrades. Most commercial building owners start here.
- Level 3, Detailed Analysis of Capital-Intensive Modifications: A deep engineering study used when major equipment replacements or building renovations are on the table. It includes detailed energy modeling and investment-grade cost projections.
Residential audits don’t follow this tiered system as formally but typically fall somewhere between a Level 1 and Level 2 in scope.
What a DIY Assessment Can Cover
You can catch many energy problems yourself before deciding whether to hire a professional. The Department of Energy recommends starting with a room-by-room walkthrough, checking for drafts along baseboards, where walls meet ceilings, around windows and doors, and near electrical outlets and light switches. On the outside, look for gaps where different building materials meet, such as where siding meets the foundation or where a chimney passes through the wall.
Checking wall insulation takes a bit more effort. Turn off the circuit breaker for a given wall’s outlets, confirm the power is off, then remove an outlet cover plate and gently probe into the wall cavity with a thin stick or plastic crochet hook. If you feel resistance or pull back bits of insulation material, you know something is there. If the cavity feels empty, that wall is uninsulated.
In the attic, look for insulation depth and coverage, check that the attic hatch is insulated and weather-stripped, and verify that openings around pipes, ductwork, and chimneys are sealed. Make sure attic vents aren’t blocked by insulation that’s been pushed against them. For ductwork in unconditioned spaces, look for dirt streaks near seams, which indicate air leaks. Also check that your furnace filter is clean and examine whether your lighting uses efficient LED bulbs.
A DIY assessment is useful for spotting obvious problems but can’t replace the precision of a blower door test or thermal imaging. If your energy bills seem high relative to your neighbors’ or your home was built before modern insulation codes, a professional audit will catch things you can’t see or feel.
How Much Energy Audits Actually Save
The savings depend entirely on what’s wrong and what you fix. Research from Lawrence Berkeley National Laboratory puts some concrete numbers on common upgrades. Adding ceiling and wall insulation in homes that need it reduced annual energy consumption by 12 to 21%. Furnace efficiency improvements saved 4 to 14% of annual gas use. Comprehensive weatherization packages (air sealing, insulation, duct sealing done together) saved a median of about 4,020 kWh of electricity per year, roughly 16% of a home’s annual electrical consumption.
Window replacements, often assumed to be a top priority, delivered more modest returns of 2 to 5% energy savings. That’s why audit reports typically rank air sealing and insulation well above windows in cost-effectiveness. The audit’s real value is telling you which upgrades give the biggest return for your specific home rather than guessing.
Tax Credits and Auditor Qualifications
Under the Energy Efficient Home Improvement Credit (Section 25C of the tax code), you can claim up to $150 per year for the cost of a qualified home energy audit. This is part of a broader annual cap of $1,200 for energy-efficient home improvements, which also covers doors, windows, insulation, and other upgrades with their own sub-limits.
To qualify for the credit, the audit must be performed by a certified home energy auditor. The Department of Energy maintains a list of recognized certification programs, and the auditor’s written report must include an attestation of their certification. Recognized credentials include the Building Performance Institute’s Building Analyst and Energy Auditor certifications, RESNET’s Home Energy Rater certification, the Association of Energy Engineers’ Certified Energy Auditor designation, and several others. When hiring an auditor, ask which DOE-recognized certification they hold, especially if you plan to claim the tax credit.