Before You Spend Anything on Home Upgrades, Get a Home Energy Audit. Here Is Why.

Quick Answer: A home energy audit is a professional assessment of how your home uses and loses energy, conducted by a certified energy auditor using diagnostic equipment including a blower door, duct leakage test, and thermal imaging camera. The audit produces a prioritized list of efficiency improvements ranked by potential energy savings and return on investment. The report it generates is the most reliable basis for deciding which upgrades to pursue and in what order. It can also document the conditions some local rebate programs ask for. Ongaro & Sons is a licensed C-10 electrical and C-20 HVAC contractor based in Petaluma, CA, serving Marin, Sonoma, and Napa County since 1932.

There is a pattern that plays out repeatedly in North Bay homes, whether in Sonoma County or Marin County. A homeowner decides to improve their home’s comfort and energy efficiency, picks an upgrade that seems logical, like a new HVAC system or better windows, spends a significant amount of money, and then discovers that the problem they were trying to solve is largely unchanged. The house is still uncomfortable in certain rooms. The energy bills are still higher than they should be.

In most cases, the underlying problem is air leakage and inadequate insulation in the building envelope. No amount of HVAC equipment efficiency overcomes a house that’s leaking conditioned air through the attic, walls, and foundation. And windows, despite absorbing most of the marketing budget in the home improvement category, rarely deliver the energy savings that insulation and air sealing do.

A home energy audit finds the actual problems. It measures them objectively, ranks them by impact, and tells you what to fix first. Done before any upgrade decision is made, it prevents the most expensive mistake homeowners make: solving the wrong problem.

What Is a Home Energy Audit?

A home energy audit is a systematic evaluation of a home’s energy performance by a trained professional using diagnostic equipment. The auditor assesses the building envelope (walls, attic, foundation, and windows), the HVAC system, water heating, lighting, and appliances, producing a data-driven report that identifies energy losses, quantifies their impact, and prioritizes upgrades by cost-effectiveness.

The term is sometimes used loosely to describe anything from a utility company’s online questionnaire to a full professional diagnostic. The distinction matters, because the online self-assessment tools are essentially guesses based on home age and size, while a professional audit with physical diagnostic testing is an actual measurement of your specific home’s performance.

What Are the Different Types of Home Energy Audits?

Utility-sponsored basic audit. PG&E, Sonoma Clean Power, and Marin Clean Energy (MCE) all offer no-cost or low-cost basic energy assessments that typically involve a phone or online consultation, bill analysis, and generic recommendations based on home type. These are useful for identifying obvious opportunities but don’t involve physical testing. They are a starting point, not a diagnostic. Marin County homeowners should check with MCE specifically, as Marin’s community choice aggregator has its own assessment programs separate from PG&E’s.

Walk-through audit. A professional auditor visits the home, conducts a visual inspection of insulation, HVAC equipment, windows, and the building envelope, and produces a basic report. No diagnostic equipment is used. Better than a utility questionnaire, but it misses the invisible problems that diagnostic testing reveals.

Comprehensive diagnostic audit. The full professional audit, involving a blower door test, duct blaster test, thermal imaging, combustion safety testing, and complete systems assessment. This is what the term “home energy audit” should mean and what some rebate programs ask for. This is the only audit worth investing in if you’re making decisions about significant home improvements.

The Building Performance Institute (BPI) and RESNET are the primary national certification bodies for home energy auditors. A BPI-certified or RESNET-certified auditor has completed standardized training in diagnostic testing protocols and building science fundamentals.

What Does a Professional Home Energy Audit Actually Involve?

A comprehensive audit takes three to five hours for a typical single-family home. Here is what happens during the visit:

Blower door test. A large fan mounted in the front door frame depressurizes the home by pulling air out. The fan measures the volume of air flowing through it to reach a target pressure differential, which tells the auditor how airtight the building envelope is. Leakier homes require more airflow to reach the test pressure. While the house is under negative pressure, the auditor uses a smoke pencil or thermal camera to locate specific leakage points: the top plates of interior walls, recessed lighting cans, attic hatches, electrical penetrations, and plumbing chases. This test finds problems that are completely invisible without it.

Duct blaster test. Similar in principle to the blower door, but applied to the duct system. The auditor seals all the registers and grilles in the home and pressurizes the duct system to measure how much air is leaking out through duct joints and seams rather than reaching the intended supply registers. The U.S. Department of Energy estimates that typical homes lose 20 to 30 percent of conditioned air through duct leakage. The duct blaster quantifies your home’s specific duct leakage and locates where the losses are occurring.

Thermal imaging. An infrared camera shows temperature differences on wall and ceiling surfaces. Under the right conditions, typically during a blower door test when airflow is occurring through the envelope, thermal imaging makes insulation gaps, missing insulation, and air infiltration paths visible as temperature patterns on the interior surface. Thermal imaging finds the wall cavities with no insulation, the attic bypasses above partition walls, and the rim joists that were never insulated.

HVAC assessment. The auditor evaluates the heating and cooling equipment: age, condition, measured efficiency, duct condition, filter condition, and whether the equipment is properly sized for the home’s actual load. Oversized HVAC equipment is common and causes short cycling, poor humidity control, and uneven temperatures. The assessment produces a clear picture of whether the equipment is performing acceptably or approaching the point where replacement makes economic sense.

Water heating assessment. The auditor evaluates water heater age, fuel type, location, and insulation. For homes with gas water heaters, the assessment includes combustion safety testing to confirm the unit is drafting properly and not back-drafting combustion gases into the living space.

Combustion safety testing. Any gas appliance that combusts fuel inside the home, including furnaces, water heaters, boilers, and gas ranges, is tested under worst-case depressurization conditions to confirm it’s not creating a carbon monoxide or backdrafting risk. This is required for a comprehensive audit and is a genuine safety function independent of energy efficiency.

Lighting and appliance inventory. The auditor documents lighting types throughout the home and major appliance age and efficiency. Lighting is typically the lowest-cost, fastest-payback upgrade category; appliances are longer-term replacements timed to end-of-life.

What Does a Home Energy Audit Report Include?

A professional audit report provides:

Measured blower door result in air changes per hour (ACH50), with comparison to code standards and efficiency program thresholds
Measured duct leakage as a percentage of system airflow
Thermal imaging findings with specific locations identified
HVAC system assessment and remaining useful life estimate
Prioritized list of recommended upgrades ranked by projected energy savings, estimated cost, and payback period
Rebate and incentive programs the home qualifies for based on current equipment and planned upgrades
In some cases, a projected Home Energy Score (the DOE’s 1-to-10 scale rating of home energy efficiency) before and after recommended improvements

The report is the document you bring to contractors when soliciting bids for specific upgrades. It establishes baseline conditions, identifies the work needed, and gives contractors a shared reference point that reduces the scope ambiguity that leads to change orders and surprises.

What Upgrades Does a Home Energy Audit Typically Flag?

In the North Bay’s older housing stock, whether in Sonoma or Marin County, the most commonly identified improvement opportunities are:

Attic insulation and air sealing. The majority of existing homes in both Sonoma and Marin counties are under-insulated by current standards, and most have significant air leakage between the living space and attic through top plates, recessed lights, attic hatches, and mechanical penetrations. Air sealing before adding insulation is critical: adding insulation on top of a leaky attic ceiling doesn’t eliminate the air movement, it just hides it. This upgrade category typically delivers the best return on investment of any single home improvement in older homes.

HVAC replacement or upgrade. Homes with aging equipment, improperly sized systems, or gas heating equipment in a market trending toward electrification are frequently flagged for heat pump replacement. An audit that documents current HVAC performance also establishes the baseline needed for heat pump rebate applications.

Heat pump water heater. Replacing a standard gas or electric resistance water heater with a heat pump water heater is one of the highest-rebate, fastest-payback electrification upgrades available. A heat pump water heater uses roughly 70 percent less electricity than a standard electric resistance unit.

Duct sealing. When duct leakage testing reveals significant losses, duct sealing (and in some cases duct replacement) is recommended. This improves HVAC efficiency without replacing the equipment itself and is frequently a prerequisite for other efficiency upgrades to perform as projected.

Window and door improvements. Despite heavy marketing, windows are typically not the highest-priority upgrade in most homes. The audit’s blower door results usually show that window frame leakage is a fraction of the total envelope leakage, most of which occurs at unsealed attic bypasses and wall penetrations. That said, single-pane windows in older homes do represent meaningful heat gain in summer, and replacement may be recommended in conjunction with other envelope work.

How Does an Audit Help With Rebates?

Some incentive programs ask for documentation of current conditions, or audit findings that establish baseline performance, before upgrades are installed.

More practically, an audit tells you exactly which upgrades your home needs and which rebate programs apply to each one. Without an audit, you’re guessing at which programs apply and potentially leaving money on the table by pursuing upgrades that don’t qualify or missing more lucrative upgrade pathways. The audit is the map; the rebates are the destinations.

What Rebates and Incentives Are Available to Sonoma and Marin County Homeowners?

Programs change frequently. Information below reflects October 2026. Verify current availability before scheduling.

The federal tax credits for heat pumps, heat pump water heaters, insulation, electrical panels, solar and home batteries ended on December 31, 2025. Most statewide rebates have also closed. TECH Clean California and the federally funded home electrification rebates for single-family homes are fully reserved, and the SGIP battery rebates for PG&E customers are closed or waitlisted.

Local programs are still running:

MCE (Marin and Napa County) offers rebates on heat pump water heaters and heat pump heating and cooling. Ongaro & Sons is a participating contractor and can apply for them while funds last.
Sonoma Clean Power offers rebates on heat pump water heaters, with larger amounts for income-qualified customers.
BayREN’s EASE Home program covers most of the cost of efficiency upgrades for income-qualified households.
PG&E’s Energy Savings Assistance program provides no-cost upgrades for income-qualified customers.

Check The Switch Is On or your energy provider’s website before you schedule work, and ask which programs apply to your home when you request an estimate.

What Are the Community Choice Aggregators and How Do Their Programs Differ from PG&E?

This is a detail specific to Sonoma and Marin counties that many homeowners don’t fully understand about their electricity service.

Sonoma Clean Power (SCP) is the community choice aggregator serving most of Sonoma County. Marin Clean Energy (MCE) is the community choice aggregator serving most of Marin County. In both cases, residents who haven’t opted out receive their electricity supply from the CCA, while PG&E continues to deliver the electricity through its existing grid infrastructure and handles billing, metering, and distribution services. You pay one bill, but two entities are involved.

Both SCP and MCE operate their own customer programs and rebates separate from PG&E’s programs. SCP has offered rebates for electric vehicles, EV chargers, electric appliances, and smart energy management programs. MCE has run similar programs for Marin customers, with a particular focus on EV adoption, heat pump installations, and home electrification. PG&E no longer lists rebates for heat pumps or heat pump water heaters, so your CCA is usually the place to start.

Before pursuing any major electrification upgrade, Sonoma County homeowners should check Sonoma Clean Power’s current programs, and Marin and Napa County homeowners should check MCE’s current programs. Programs and amounts change, so confirm current terms before you schedule work.

How Should You Sequence Upgrades After an Audit?

The sequence of efficiency upgrades matters as much as the upgrades themselves. The standard best-practice order from the California Energy Commission and building performance professionals:

First: air sealing and insulation. Reducing the thermal load of the building envelope makes every subsequent system upgrade more effective. A heat pump installed in a leaky, under-insulated home has to work significantly harder than the same unit in a properly sealed home. Doing envelope work first means you may also be able to right-size HVAC equipment to a smaller, less expensive system.

Second: HVAC replacement. Once the building load is reduced through envelope improvements, replace aging or inefficient heating and cooling equipment. The audit’s load calculation, adjusted for the envelope improvements, establishes the correct equipment size.

Third: water heating. Heat pump water heater replacement is often a high-rebate, high-return upgrade that can proceed in parallel with HVAC if budget allows, since it’s a standalone system.

Fourth: electrical infrastructure. Panel upgrades, EV charger installation, and solar or battery storage are typically installed after the load picture is clear from the envelope and HVAC work.

Fifth: remaining upgrades. Lighting, appliances, and windows are typically the lowest-priority category from a pure return-on-investment standpoint and can be addressed as equipment reaches end of life.

Deviating from this sequence isn’t always wrong, particularly if specific equipment is failing and replacement is urgent. But following the sequence when possible maximizes the efficiency gain from each investment and avoids the common outcome of installing more HVAC capacity than a properly upgraded envelope requires.

Who Should Perform Your Home Energy Audit?

For a comprehensive diagnostic audit that satisfies rebate program documentation requirements, look for auditors certified by BPI (Building Performance Institute) or RESNET. These certifications require demonstrated knowledge of building science, diagnostic testing procedures, and combustion safety. Where a rebate program asks for audit documentation, it generally expects a certified professional.

Confirm before booking that the audit includes physical diagnostic testing, specifically a blower door test and duct leakage test, not just a walk-through. Some companies advertise “energy audits” that involve only a visual inspection. The visual inspection without physical testing doesn’t measure the building envelope or duct performance and won’t satisfy the documentation requirements for major rebate programs.

Ask whether the audit report includes rebate program guidance specific to your situation. A good auditor knows which programs your upgrades qualify for and can help you understand how to sequence the work to maximize eligibility.

The certified auditor and the contractor who performs the upgrades are not always the same company. A common and effective approach is to have an independent BPI or RESNET auditor produce the diagnostic report, then take that report to a licensed multi-trade contractor, like an electrical and HVAC firm, to implement the prioritized upgrade list. The auditor tells you what your home needs. The contractor does the work. Keeping those two roles clearly defined protects you from contractors who both assess and sell their own recommendations without independent validation.

What Does a Home Energy Audit Cost in Sonoma and Marin Counties?

A comprehensive diagnostic audit from a BPI or RESNET-certified auditor is modest relative to the scale of upgrade decisions it informs. Some utility programs subsidize or fully cover the cost of audits for customers who meet certain criteria, so confirming current program availability through PG&E and your county’s CCA (Sonoma Clean Power for Sonoma County, Marin Clean Energy for Marin County) before paying out of pocket is worthwhile.

An audit that correctly prioritizes a major upgrade project and identifies applicable rebates pays for itself many times over in the first year.

Frequently Asked Questions

What is a home energy audit? A home energy audit is a professional assessment of how a home uses and loses energy, conducted by a certified auditor using diagnostic equipment. A comprehensive audit includes a blower door test to measure building envelope airtightness, a duct leakage test, thermal imaging to locate insulation gaps and air leaks, HVAC system assessment, and combustion safety testing. It produces a prioritized report of efficiency improvements ranked by savings potential and return on investment.

How long does a home energy audit take? A comprehensive diagnostic audit takes three to five hours for a typical single-family home. Basic walk-through audits without diagnostic equipment take less time but provide less useful information.

How much does a home energy audit cost in Sonoma or Marin County? An audit from a certified professional is a relatively small upfront investment compared to the upgrade decisions it informs. PG&E, Sonoma Clean Power (for Sonoma County homeowners), and Marin Clean Energy (for Marin County homeowners) may subsidize or fully cover the audit cost for qualifying customers. Check availability before paying out of pocket. Get a written proposal that clearly defines what the audit includes: blower door, duct testing, thermal imaging, and a written report with upgrade recommendations.

Which rebates can a home energy audit help with? A professional audit documents the baseline conditions some programs ask for, including Sonoma Clean Power programs (for Sonoma County homeowners), MCE programs (for Marin and Napa County homeowners) and BayREN’s EASE Home program for income-qualified households. The federal tax credits for efficiency upgrades ended on December 31, 2025.

Is a home energy audit worth it? Yes, particularly before making any significant home improvement investment. The audit prevents the common mistake of pursuing upgrades that don’t address the actual source of energy loss or discomfort. It also identifies rebate opportunities that often exceed the cost of the audit many times over. For a home planning multiple upgrades, an audit is the most cost-effective first step available.

What is the difference between a home energy audit and a home energy score? A home energy score is a 1-to-10 rating of a home’s energy efficiency, produced by a DOE-certified assessor and based on physical home characteristics. It’s often generated as part of a comprehensive audit. The audit is the process; the home energy score is one of the outputs. Some real estate transactions now include a home energy score as part of the listing disclosure.

What is Sonoma Clean Power, and what is Marin Clean Energy? Sonoma Clean Power (SCP) is the community choice aggregator serving most of Sonoma County. Marin Clean Energy (MCE) is the equivalent organization for Marin County. In both cases, residents receive their electricity supply from the CCA while PG&E delivers it through the existing grid infrastructure. Both SCP and MCE have their own customer rebate programs separate from PG&E’s, and with PG&E no longer listing most equipment rebates, the CCA is usually where to start. Sonoma County homeowners should check SCP; Marin County homeowners should check MCE. Always confirm before pursuing a major efficiency upgrade.

Do I need an energy audit before applying for California rebates? Some rebate programs require audit documentation to establish baseline conditions and verify upgrade eligibility. Others, particularly point-of-sale rebates for specific equipment, don’t require a prior audit but do require equipment specifications and installer documentation. An auditor familiar with current California programs can clarify which documentation each program requires for your specific upgrade plan.

What is the blower door test? A blower door test uses a calibrated fan mounted in the front door to depressurize a home and measure how airtight the building envelope is. The result is expressed as air changes per hour at 50 Pascals of pressure (ACH50). It identifies the overall level of air leakage and, when combined with thermal imaging, locates specific leakage points throughout the envelope.

Start Your Home Efficiency Project in Sonoma or Marin County

Ongaro & Sons is a licensed C-10 electrical and C-20 HVAC contractor based in Petaluma, CA, serving Marin, Sonoma, and Napa County since 1932. We have been Diamond Certified since October 2016, and we are a Trane Comfort Specialist and a Mitsubishi Diamond Contractor Elite. We handle the upgrade side of home electrification projects, including HVAC replacement, electrical panel upgrades, EV charger installation, and solar integration, and can work from an independent audit report or help coordinate one as the first step.

If you already have an audit report and are ready to move forward, schedule a consultation to discuss the recommended upgrades and get a scope of work.

If you’re starting from scratch, contact us and we can talk through whether an independent audit or a focused look at one system makes more sense for your home.

Home Energy Audit: Marin And Sonoma County Guide