Your HVAC system accounts for 40–60% of your home's energy use, making it one of the most critical components a home inspector evaluates. A thorough inspection protects you from inheriting expensive repairs or inefficient equipment that'll drain your wallet for years. Knowing what inspectors actually check helps you ask better questions and spot red flags before you buy.
What Inspectors Examine During an HVAC Inspection
A professional home inspector doesn't just listen to your system run. They perform a systematic walkthrough of equipment, connections, and safety features that determine whether your heating and cooling will function reliably.
The inspection typically takes 30–45 minutes and covers both outdoor and indoor components. You can expect the inspector to access your attic, basement, and utility closet to examine everything from ductwork to electrical connections.
The Main Components Getting Checked
Outdoor Unit (Condenser)
Inspectors look for rust, corrosion, and physical damage on the exterior casing. They verify the unit sits on a level pad and check that it has adequate clearance—typically 2–3 feet on all sides—for proper airflow. Debris like leaves, dirt, or overgrown plants around the unit gets noted, as these reduce efficiency by 5–15%.
Indoor Unit (Furnace or Air Handler)
The inspector examines the blower compartment for dust buildup, checks filter condition, and listens for unusual noises during operation. They also verify that combustion gas is properly vented if you have a gas furnace—a critical safety check. Age of the unit matters too; most systems last 15–20 years, and inspectors note when replacement may be approaching.
Thermostat
The inspector tests the thermostat's ability to trigger heating and cooling cycles. They'll verify it's level, properly mounted, and responsive to temperature adjustments. Older mercury thermostats sometimes get flagged for potential hazards.
Ductwork and Connections
Visible ductwork in basements, attics, and crawlspaces gets examined for leaks, disconnections, and proper insulation. Leaky ducts can waste 15–30% of conditioned air before it reaches your living spaces. Inspectors check that ducts are adequately sealed with mastic or metal tape, not cloth duct tape.
Refrigerant Lines
Copper lines connecting indoor and outdoor units should be intact, properly insulated, and without visible leaks or kinks. Refrigerant line damage is expensive to repair and indicates potential environmental concerns.
Safety Checks That Matter
Gas Line Inspection
For gas furnaces, inspectors verify proper connection at the meter or tank, check for visible leaks using a soapy water test, and ensure gas shutoff valves are accessible and functional.
Combustion Safety
Inspectors confirm that furnaces have proper venting to the exterior and that there's no backdrafting—where exhaust gases reverse into the home instead of venting outside. Carbon monoxide concerns are taken seriously and may warrant a follow-up test.
Electrical Connections
Breaker size, wire connections, and proper grounding all get evaluated. Improper electrical setup can be a fire hazard.
Red Flags That Appear in Reports
- System won't turn on: May indicate electrical issues or thermostat problems ($150–$500 to diagnose)
- Age over 15 years: Declining efficiency, replacement likely within 5 years ($3,000–$7,500 for a new system)
- Refrigerant leaks: Requires immediate service; could indicate major compressor failure ($300–$2,000+)
- Disconnected or severely kinked ductwork: Reduces efficiency and comfort noticeably
- Missing duct insulation in unconditioned spaces: Leads to energy loss and higher utility bills
- Inadequate clearance around outdoor unit: Blocks airflow, reduces cooling capacity by up to 25%
What You Can Do Before the Inspection
Change or check your air filter before the inspector arrives—a clogged filter can mask other issues and might cause the inspector to recommend an unnecessary service call. Document when the system was last serviced and what work was done. If you know the brand and model, have that information ready.
Finding a Qualified HVAC Inspector
Look for inspectors certified by NAHI (National Association of Home Inspectors) or ASHI (American Society of Home Inspectors). A standard home inspection runs $300–$500 and typically includes HVAC evaluation. If you need a specialist inspection of just the HVAC system, expect $150–$300. Mercoly helps you compare and find trusted Home Inspection providers in one place, making it easier to get multiple quotes and read verified reviews.
Frequently Asked Questions
Q: Can a home inspector test refrigerant levels? Home inspectors typically don't perform refrigerant pressure tests—that's a licensed HVAC technician's job—but they'll note if the system seems to be undercharging or overheating during operation.
Q: How do I know if my ducts are leaking? Look for visible disconnections or torn insulation; during heating or cooling, feel around duct seams with your hand near the attic or basement to detect air leaks, or request a blower door test from an HVAC specialist ($200–$400).
Q: Should I get a separate HVAC inspection beyond the general home inspection? If the system is over 10 years old, has been repaired frequently, or the general inspector raises concerns, a dedicated HVAC technician inspection ($150–$300) is worth the investment before closing.
Start comparing inspectors today to protect your investment in your new home.