Duct and vent repair: what to know

What the job involves, what changes the price, and what to ask a pro.

What duct and vent repair is

Duct and vent repair seals leaking ducts, reconnects loose sections, replaces damaged vents and insulates runs, so heated or cooled air reaches the rooms it is meant for. It is a common fix for a house where some rooms are always too hot or too cold.

Signs you need it

  • A room is noticeably hotter or colder than the rest of the house, even with the registers open.
  • The air from the furnace or air handler is weak, or the system runs longer than it should to reach temperature.
  • You can feel air leaking near a duct joint, or you see dust streaks around a duct seam or a register.
  • The duct in an attic or crawl space sags, is crushed, or has come apart at a joint.
  • A register is cracked, bent or no longer sits flush with the wall or ceiling.
  • The ducts feel very warm or cold to the touch in an unconditioned space.

What the pro does

  • Trace the duct system with a smoke pencil or a fog machine to find the leaks at the joints and seams.
  • Measure the airflow at the registers and the static pressure at the furnace or air handler to see how the system is working.
  • Reconnect any loose or pulled-apart joints, and replace crushed or torn sections of flexible duct.
  • Seal the joints and seams with mastic or foil-backed tape, and replace damaged register boots or grilles.
  • Insulate ducts in unconditioned spaces that are uninsulated or have worn insulation.
  • Test the airflow again, and confirm the rooms get the air they were designed to receive.

What changes the price

Every job is different, so we do not publish prices. These are the things that move the quote up or down.

  • Number and location of the leaks, since each leak has to be found and sealed.
  • Type of duct, such as sheet metal, flexible duct or fiberglass board, which changes the repair method.
  • Access to the ducts through the attic, crawl space or wall cavity.
  • Whether a damaged section needs to be replaced rather than sealed.
  • Number of registers that need replacing, and the style of each.
  • Insulation needs in the unconditioned runs.
  • Whether the fault is caused by undersized ducts or airflow imbalance, which needs more work than leak sealing.

What a written quote should spell out

  • The leak locations found, with a count and a description of each.
  • The sealing method used on each joint, and the materials named.
  • Any section replaced, with its length and type.
  • Any register or grille replaced, listed by room.
  • Insulation added, with the location and the material.
  • Post-repair airflow readings or a written statement of the results.

Questions to ask before you hire

  • How will you find the leaks, and can you show me where they are?
  • What sealing method do you use, and why is it better than cloth duct tape?
  • Will you replace the crushed or damaged sections, or only seal them?
  • Will you insulate the ducts in the attic or crawl space after the repair?
  • Will you measure the airflow before and after the repair?
  • Will you check the return air path for leaks or restrictions?
  • Will you give me the before and after readings in writing?

Red flags

  • The pro seals the joints with cloth duct tape, which dries out and fails.
  • The pro does not test the airflow or find the leaks before quoting a repair.
  • The pro quotes a whole new duct system without first sealing and testing the existing one.
  • The pro leaves insulation off the ducts in an unconditioned attic or crawl space after the repair.

What you can do yourself

You can check the vents for dust streaks, clear furniture and debris from around the registers, and keep the registers and grilles open. You can also replace a damaged register cover if it is a simple snap-in or screw-in type. Sealing joints, reconnecting ducts, insulating runs and working inside the attic or crawl space belong to a licensed HVAC contractor.

Licenses and permits

Duct and vent repair is commonly done by licensed HVAC contractors, and it may need a permit for larger changes. Check with your state or local licensing agency for the requirements that apply to your repair.

Duct and vent repair questions

Can I seal duct leaks with tape?

Use foil-backed tape or mastic, not cloth duct tape. Cloth tape dries out and lets go within a few seasons. A technician can find the leaks with a smoke test and seal them correctly.

How do I find a duct leak?

Look for dust streaks near joints, feel for air at seams when the system runs, and check for cold or hot spots in the rooms. A technician uses a smoke pencil or a fog test to find the leaks reliably.

Why does my attic duct feel hot in summer?

Ducts in an attic get hot from the roof and attic air. Insulation and sealed joints keep the cooled air from warming up before it reaches the rooms.

Is a leaky duct a safety issue?

Leaks can pull unconditioned air, dust and sometimes attic or crawl space air into the system. Return leaks can also change the pressure in the house and affect how gas appliances vent. A technician checks the duct system and the return path to be sure the house is not under negative pressure.

About this guide

This national guide is written and checked by infinibell. Rules and conditions differ by place, so local pros are credited on guides for the cities they serve, not on national ones.

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