Indoor Air Quality

What Is Duct Sealing (Mastic / Aerosolized Sealant)?

Definition

Duct sealing closes gaps, loose joints, and holes in ductwork using mastic paste or an aerosolized sealant injected and cured inside the duct system, stopping conditioned air from leaking into unconditioned attics, crawlspaces, or wall cavities before it ever reaches a room.

Why it matters for your home

In homes with ducts running through unconditioned attics and crawlspaces — common construction in the Tualatin Valley — leakage losses are commonly estimated at 20-30% of the air the system moves, meaning you can be paying to heat or cool a fifth to a third of your air that never reaches a living space.

What to do about it

A duct test measures your actual leakage rather than guessing — worth doing before assuming weak airflow is a duct-cleaning problem instead of a sealing problem.

Money term — the details

How is duct sealing different from duct cleaning?

Cleaning removes debris and buildup inside ducts that are otherwise intact; sealing closes physical leaks and gaps. If weak airflow comes from leaky or undersized ducts, cleaning won't touch it — sealing or duct correction is the right tool.

Is duct sealing worth doing before replacing my HVAC system?

Often yes — a leaky duct system can undercut even a brand-new, high-efficiency furnace or heat pump's real-world performance, so sealing first (or alongside replacement) protects the investment you're about to make.

See it in context Duct Sealing

Sources

Site content — service-faqs.ts (duct sealing)

This definition is pending licensed-trade technical review. It's sourced from our own published service and guide content, not invented — but hasn't yet been signed off by a licensed HVAC reviewer.

Back to the full glossary

One call does it

Heard this term in a quote?

Bring it to Best Owner Direct for an honest, no-obligation second look — we'll translate every line item, no pressure.

Book Service Call (503) 442-5964

Locally operated · Licensed CCB# 199049 · 1-Year Workmanship Warranty