HVAC Inspection Checklist: What to Check & How to Document It

HVAC systems are where home inspectors find some of the most expensive problems — and where clear documentation matters most. A cracked heat exchanger can cost $3,000+ to fix. A failing compressor means a full system replacement. And a misjudged "operational" call on a system that dies two weeks after closing? That's a callback you don't want.

This checklist covers what to inspect, what to document, and the common defects that separate thorough inspectors from ones who just flip the thermostat and move on.

Field reality: HVAC is the #2 category for inspection disputes (after roof and structure). Clear documentation with photos and specific measurements protects you. "System appeared to operate normally" won't hold up if the compressor fails next month. "Measured 18°F temperature differential at supply and return registers; system cycled properly with no unusual sounds or odors" will.

Before You Start: Pre-Inspection Setup

Check the Thermostat Setting

Note the current setting and mode. If the system hasn't been running, you'll need a few minutes for it to reach operating temperature/pressure before taking measurements.

Check the Air Filter

Location, type, size, and condition. A clogged filter affects everything — airflow, efficiency, temperature differential, and system longevity. Document the filter condition first because it explains other findings.

Common filter locations: Return air grille, inside the blower compartment, at the air handler, or in a dedicated filter rack.

Note System Age

Find the manufacturer's data plate. Most units encode the manufacture date in the serial number (lookup guides vary by manufacturer). Average life expectancy: furnaces 15–20 years, AC condensers 15–20 years, heat pumps 12–15 years.

Pro tip: If you can't decode the serial number in the field, photograph the data plate. You can look it up later. Don't guess the age.

Heating System Inspection

Furnace (Gas or Electric)

1. Visual Inspection

• Cabinet condition: rust, corrosion, damage
• Burner flames (gas): should be blue with small yellow tips. Orange or yellow flames indicate incomplete combustion (dirty burners or cracked heat exchanger)
• Burn marks or soot around the cabinet (indicates combustion problems)
• Proper clearance from combustibles

2. Operational Test

• Run the system through a complete cycle: call for heat → ignition → blower activation → temperature rise → thermostat satisfaction → shutdown
• Listen for unusual sounds: banging (delayed ignition), squealing (belt or bearing), rattling (loose components)
• Check for unusual odors: burning smell (dust burn-off is normal on first seasonal start, persistent smell is not)

3. Heat Exchanger (Visual)

• Look through the burner opening with a flashlight for visible cracks, rust, or holes
• Check for flame disturbance when the blower kicks on (flame flicker or rollout suggests a cracked exchanger)
• Note: Visual inspection has limits. You can't see every surface. Document what you CAN see and note the limitation in your report

4. Venting

• Flue pipe material and condition (single-wall vs B-vent)
• Proper slope toward chimney/exterior (minimum 1/4" per foot upward)
• Connections secure, no gaps or rust-through
• Draft test: hold a match or smoke pen near the draft hood — smoke should pull into the flue, not push into the room

5. Temperature Rise

• Measure supply and return air temperatures at the plenum
• Calculate temperature rise: supply minus return
• Compare to manufacturer's specifications (typically 35–75°F for gas furnaces, 20–30°F for heat pumps)
• Document both temperatures and the calculated rise

Boiler Systems

• Pressure gauge reading (typically 12–15 psi cold)
• Temperature gauge reading
• Relief valve presence and piping (must discharge to within 6" of floor)
• Expansion tank condition
• Visible leaks at piping, valves, and connections
• Circulator pump operation

Cooling System Inspection

Condenser Unit (Exterior)

1. Visual Inspection

• Unit level and stable on pad
• Coil condition: bent fins, debris, vegetation clearance (minimum 2 feet on all sides)
• Refrigerant line condition: insulation on suction line (large line), no oil stains at connections
• Electrical connections: disconnect present, wiring condition
• Fan blade condition and motor operation

2. Operational Test

• Run the system for at least 15 minutes before taking temperature readings
• Compressor should run smoothly — no hard starting, short cycling, or unusual vibration
• Fan should move air freely with no rattling or wobbling
• Listen for hissing or bubbling sounds (possible refrigerant leak)

Evaporator Coil (Interior)

• Condensate drain: flowing freely, properly routed, and terminated appropriately
• Condensate pan: no standing water, no algae growth, no overflow evidence
• Coil condition (if accessible): frost or ice indicates airflow restriction or refrigerant issue

Temperature Differential Test

This is your most important cooling measurement.

1. Place thermometer in the supply register closest to the air handler
2. Place second thermometer in the return air grille
3. Wait 15+ minutes of operation for stable readings
4. Calculate: supply temperature minus return temperature

Expected range: 14–22°F differential

• Below 14°F: Low refrigerant, dirty coil, restricted airflow, or failing compressor
• Above 22°F: Restricted airflow (dirty filter, collapsed duct) or low blower speed
• Document both temperatures and the calculated differential

Important: Don't run AC when outdoor temperature is below 60°F — you can damage the compressor. Note this limitation in your report if applicable.

Ductwork Inspection

Accessible Ductwork

• Material and condition: Sheet metal, flex duct, or duct board. Check for disconnections, tears, and crushing (flex duct in crawl spaces is notorious for this)
• Connections: Properly sealed at joints? Duct tape (ironically) is not an approved sealant. Mastic or metal-backed tape is correct
• Insulation: Present and intact on ducts in unconditioned spaces (attic, crawl space)
• Support: Flex duct should be supported every 4 feet maximum with no sagging

Supply and Return Registers

• Airflow at each supply register (hold a tissue near it — should deflect noticeably)
• Return air pathways: adequate returns in each living area? Many older homes have only one or two central returns
• Register condition: damaged, painted shut, or blocked by furniture

Common Duct Defects to Document

1. Disconnected flex duct in attic — you're cooling/heating the attic instead of the house
2. Crushed duct in crawl space — room gets no air, homeowner thinks the system is failing
3. Missing insulation on attic ducts — sweating ducts, moisture damage, energy loss
4. Bathroom fan duct terminated in attic — moisture dumping into attic space (extremely common, always document)

Ventilation

Bathroom Exhaust Fans

• Operation (each fan)
• Airflow test: tissue paper should stick to the grille when fan is running
• Duct termination: must vent to exterior, NOT into attic, soffit, or crawl space
• Duct material: rigid or semi-rigid metal preferred; flex duct acceptable if short runs

Kitchen Ventilation

• Range hood operation (fan and light)
• Venting type: ducted to exterior vs recirculating (filter only)
• Ducted hoods: verify exterior termination
• Downdraft systems: operation and condition

Whole-House Ventilation

• If present: type (HRV, ERV, exhaust-only), operation, and filter condition
• Energy codes in many states now require mechanical ventilation in new construction

Thermostat

• Type: manual, programmable, or smart
• Operation: test both heating and cooling modes if conditions allow
• Location: should be on an interior wall, away from supply registers, windows, and direct sunlight
• Response: system should activate within 1–2 minutes of a temperature change

Red Flags That Need Immediate Documentation

These findings require clear, specific documentation with photos:

1. Carbon monoxide risk: Cracked heat exchanger, backdrafting flue, combustion appliance in sleeping area without CO detection
2. Gas leak indicators: Smell of gas, dead vegetation near gas lines, hissing sounds
3. No temperature differential on AC: System running but not cooling — compressor failure, refrigerant loss, or major duct disconnect
4. Flame rollout: Flames extending beyond the burner compartment — immediate safety hazard
5. Abandoned oil tank: Note presence and recommend environmental assessment
6. Asbestos-wrapped ductwork: Do not disturb. Document and recommend assessment by qualified professional

Documentation Best Practices

HVAC documentation needs to be specific and measurable. Vague language invites disputes.

Instead of: "Heating system operated normally." Write: "Gas furnace fired on call with blue burner flames. Temperature rise measured at 52°F (supply 128°F, return 76°F) within manufacturer's specified range of 35–65°F. System completed full cycle with proper shutdown. No unusual sounds or odors detected."

Instead of: "AC seemed weak." Write: "Temperature differential measured at 11°F (supply 67°F, return 78°F) after 20 minutes of operation — below the expected 14–22°F range. Recommend evaluation by licensed HVAC contractor."

The fastest way to document HVAC findings this specifically? Narrate them in real time. Walk up to the furnace, speak what you see, speak your measurements. Voice-first tools like ReportWalk convert that narration into structured report language — so your HVAC section reads like an expert wrote it, because an expert did. You just said it instead of typing it.

Seasonal Considerations

Summer inspections: AC is your priority. You can fully test cooling. Heating test may be limited (don't run the furnace when it's 95°F outside — just verify ignition and immediate operation).

Winter inspections: Heating is your priority. AC testing is limited when outdoor temps are below 60°F. Note the limitation clearly in your report.

Spring/Fall: Best time for HVAC inspection — you can usually test both systems fully.

The Checklist Summary

Print this or save it to your phone:

• Filter: location, type, condition
• System age: data plate photographed
• Heating: visual, operational cycle, flame color, temperature rise, venting
• Cooling: condenser condition, operational test, temperature differential
• Ductwork: material, connections, insulation, support
• Registers: airflow at each supply, adequate returns
• Exhaust fans: operation, termination
• Thermostat: type, both modes tested
• Red flags: CO risks, gas leak signs, no temp differential, flame rollout
• Photos: data plate, filter, flame color, temperature readings, defects

Want to document your HVAC findings faster? ReportWalk lets you narrate your inspection — speak the temperatures, describe the defects, and the report writes itself. Try it on your next HVAC inspection.