HVAC duct replacement: layout, access, insulation, and balancing

Compare duct-replacement bids by delivered airflow and layout, not just the number of feet of flexible duct. DOE’s Building Science Education materials identify duct-leakage testing and appropriate sealing materials as part of evaluating duct systems (DOE duct-leakage testing). ENERGY STAR’s quality-installation guidance also emphasizes measuring delivered ventilation and documenting design values (HVAC quality installation guide). Together, they support a quote that includes testing and documentation.

Scope items that change the total

Item	What the bid should state
Layout	Branch count, trunk changes, register locations, and return path
Sizing	Design airflow or load basis and equipment connection sizes
Access	Attic, crawlspace, ceiling openings, platforms, and protection
Insulation	R-value, vapor barrier, supports, and replacement of damaged insulation
Sealing	Mastic/tape at joints, boots, plenums, and equipment transitions
Commissioning	Leakage test, airflow/balance readings, and thermostat test

“Replace the ducts” can mean only damaged branches or a full supply-and-return redesign. Ask whether old plenums, boots, dampers, collars, and grilles are reused. A new branch connected to a leaking plenum will not produce the result the headline promises.

Access and restoration

Open basement ceilings make work visible and comparatively easy to inspect. Buried attic runs may require moving insulation, installing walk boards, and repairing vapor barriers. Behind finished drywall, the quote should state who opens and closes the surface and whether painting is included. Keep HVAC and drywall restoration as separate lines so a low duct number does not hide restoration work.

Insulation is part of performance. Ask how the crew supports flex duct to prevent compression and whether exposed sections receive the specified insulation. Request photos before closure. The measurement units in the quote should be clear: linear feet do not describe fittings, transitions, access, or balancing.

Balancing is the decision point

The most useful acceptance test is room-by-room airflow or pressure measurement against the design. Ask for the test instrument and the final readings. A contractor who offers a diagram and balancing report gives you something to compare; a contractor who promises “better airflow” leaves the result subjective. ENERGY STAR’s documentation requirements in its quality-installation material illustrate why design values and measured performance belong in the record.

Get two bids using the same floor plan, equipment model, and access photos. Put each total beside the number of branches, return changes, insulation, sealing, restoration, and commissioning. If replacement is being proposed because one room is hot, ask for a leakage and airflow diagnosis first. The HVAC repair cost page may help with broader context, but it does not price duct redesign.

Before work starts, ask for the old and new duct map and note which rooms are deliberately left unchanged. The map should show supply and return paths, dampers, and any transfer grilles. This makes a later comfort complaint traceable to a scope decision rather than an argument about whether the crew did enough.

Sources and limits

DOE supports duct-leakage testing and sealing evaluation. ENERGY STAR supports documented design and measured ventilation/installation checks. No national duct-replacement range is stated because layout, access, insulation, and restoration vary widely.