HVAC duct sealing: comparing accessible and aerosol sealing quotes

Start with a leakage test and a map of the duct system. The Department of Energy’s Building Science Education module explains that duct-leakage testing helps identify where sealing materials should be applied (DOE duct-leakage testing). A quote that promises “seal the ducts” without a baseline cannot show whether the work paid off.

Accessible sealing and aerosol sealing solve different access problems. Accessible work reaches joints, boots, plenums, and disconnected sections directly. Aerosol systems can address distributed leaks in connected ductwork after the system is prepared and sealed around openings. DOE describes aerosol duct sealing as a developed technology for improving airtightness in existing and new homes (DOE aerosol-sealing article). Neither source provides a national residential price; request local quotes.

Compare proposals on measured scope

Proposal line	Accessible sealing	Aerosol sealing
Baseline	Duct leakage test and visual map	Duct leakage test and equipment preparation
Work area	Joints and components the crew can reach	Connected system within process limits
Exclusions	Concealed runs, damaged insulation, inaccessible boots	Open returns, filters, registers, and areas that must be isolated
Verification	Post-seal leakage test	Post-process test and report
Restoration	Mastic/tape cure, insulation repair, access panels	Cleanup and reinstallation of removed items

The material matters. Ask whether the contractor uses code-appropriate mastic or listed tape, how damaged insulation is handled, and whether supply and return sides are tested separately. A coating over wet insulation or a loose boot does not repair the underlying problem.

What can change the quote

Access is the main variable: an open basement trunk is different from ducts buried under attic insulation or behind finished walls. System size, number of zones, register count, and whether the furnace or air handler must be isolated also affect preparation. Ask if air balancing is included. Sealing may reduce leakage while leaving a comfort problem caused by undersized or poorly balanced branches.

Avoid claims that sealing will save a fixed percentage on every home. DOE’s technology discussion supports the process, not a guaranteed bill reduction for your building. Ask for the test units, the before-and-after result, and the assumptions behind any savings estimate.

Your quote comparison tool

Make each bidder fill five cells: baseline leakage, locations included, method/material, exclusions, and post-work leakage. Choose the method that reaches the documented leaks and gives you a retest. If an aerosol bid omits preparation or testing, ask what system openings are isolated and how the crew will confirm the process worked. If an accessible bid omits concealed runs, treat its total as partial scope.

For related cleaning questions, see the published air duct cleaning cost page, while remembering that cleaning and sealing are different services. Ask for photos and test reports before paying a deposit.

Sources and limits

DOE Building Science Education supports duct-leakage testing and sealing-material placement. DOE supports aerosol sealing as a technology used to improve airtightness in occupied residences. Prices and savings are not generalized; local measured proposals are required.