2.4 HVAC & Plumbing

Heating

The inspector identifies the heat source, operates it on the normal controls, and checks for safe combustion and distribution:

The most serious furnace defect is a cracked heat exchanger — the metal barrier between combustion gases and the household air. A crack can leak carbon monoxide into the supply air; because it often justifies replacing the unit, inspectors flag any evidence (rust flaking, flame distortion when the blower starts) and recommend evaluation. Venting and clearance matter for all fuel-burning equipment: vents must slope up, be properly connected, and maintain clearance to combustibles — roughly 6 inches for single-wall connectors and about 1 inch for double-wall (Type B).

Backdrafting, disconnected flue sections, and rust at the draft hood are reported.

Cooling & Distribution

Cooling is usually a split-system air conditioner or a heat pump. The inspector runs it (when outdoor temperatures allow — typically above ~60–65°F to avoid compressor damage), measuring the temperature split across the coil and checking the condensate system: the primary drain line, the secondary/auxiliary pan and drain under an attic air handler, and signs of overflow or staining. A clogged condensate line is a frequent finding. The inspector also notes the unit's age (from the data plate), insulation on the suction line, and a level, clear condenser pad.

Distribution — ductwork or piping — is checked for disconnected or crushed ducts, missing insulation on ducts in unconditioned space, and balanced supply/return. For hydronic systems, radiators and baseboards are checked for leaks and air-bleed function.

Plumbing: Supply, DWV & Water Heaters

Supply piping delivers pressurized water. The inspector identifies the material — copper, PEX (cross-linked polyethylene), or galvanized steel (which corrodes and restricts flow internally) — and reports polybutylene (poly-B), a gray plastic used roughly 1978–1995 that is prone to failure at fittings. Functional water pressure/flow is checked by running fixtures; very low pressure suggests corroded galvanized lines or supply issues.

The drain-waste-vent (DWV) system removes wastewater. Each fixture needs a trap that holds a water seal to block sewer gas, and venting so draining one fixture doesn't siphon another's trap dry. S-traps, unvented traps, and improper slopes are reported. The inspector watches drainage speed and looks for leaks at trap connections.

Water heaters are a combustion-and-pressure safety focus. Every tank needs a TPR (temperature and pressure relief) valve with a discharge tube routed downward to within a few inches of the floor, terminating in a visible location. The missing discharge tube is the most common defect; an undersized, capped, or upward-routed tube, or one made of unapproved material (no PEX in many jurisdictions, never a flexible hose), is also reported. Gas units are checked for proper venting and combustion air; the inspector notes temperature setting (scald risk above ~120°F) and whether seismic strapping is present where required.

Combustion Safety & Venting Errors

Fuel-burning appliances share a set of life-safety venting defects that the exam emphasizes because they involve carbon monoxide (CO).

The inspector looks for backdrafting (combustion gases spilling into the room instead of up the flue, sometimes confirmed at the draft hood with a smoke source), disconnected or sloped-down vent connectors (vents must rise continuously toward the chimney), single-wall connectors too close to combustibles (about 6 inches required), and orphaned water heaters — a small water heater left venting alone into an oversized chimney flue after a furnace upgrade, which can be too cold to draft and may backdraft.

Atmospheric vs. high-efficiency equipment vents differently: standard 80% AFUE furnaces and water heaters use metal flues into a chimney, while 90%+ condensing units use PVC venting that can run horizontally and produce acidic condensate requiring a drain (and sometimes a neutralizer). Mixing these up — PVC on an atmospheric unit, or a condensing unit with no condensate drain — is a defect.

Connecting Plumbing Symptoms

Like the exterior, the plumbing system rewards reading symptoms as a chain. Low flow at one fixture suggests a local aerator or valve; low flow throughout points to corroded galvanized mains or a supply problem. Slow drainage plus a gurgling sound suggests a venting defect, not just a clog. Water staining on a ceiling below a bathroom asks the candidate to trace supply, drain, trap, or wax-ring failure above. Cross-connections — where non-potable water could siphon back into the supply (a hose-bib without a vacuum breaker, a submerged inlet) — are reported because they threaten the potable water.

Throughout, the inspector runs fixtures, observes, and reports within the visual standard, recommending a licensed plumber or HVAC contractor for invasive diagnosis, hidden leaks, or equipment that cannot be safely operated — the same specialist-referral discipline used across the inspection. The inspector does not pressure-test lines, dismantle equipment, or estimate remaining compressor life; the visual operation of the system on its normal controls, plus observation of materials, venting, and leakage, defines the standard scope for both the heating/cooling and plumbing portions of the report.