Duct installation: what to know

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

What duct installation is

Duct installation adds new ducts or changes existing ones to carry heated or cooled air to the rooms that need it. The work includes sizing, sealing and insulation, so the air arrives at each room in the amount the room was designed for.

Signs you need it

  • A room has no supply register, or the register is far from the rest of the system and the room never warms or cools.
  • You are finishing a basement, adding a room or converting an attic, and the existing ducts do not reach the new space.
  • Air is weak at the far end of the house, while the registers near the furnace blow strongly.
  • The existing ducts are undersized, crushed or run through unconditioned spaces where heat is lost.
  • A new heating or cooling system is being installed, and the old ducts cannot carry the new airflow.
  • You hear whistling at the registers or the ducts feel very warm in an attic or crawl space.

What the pro does

  • Measure the rooms, check the airflow at each register and calculate the duct sizes the new layout needs.
  • Plan the duct route, including the trunk line, branch runs, boot locations and return air path.
  • Cut and fit the sheet metal or flexible duct, and hang it with straps so it does not sag or rub.
  • Seal every joint with mastic or foil-backed tape, and test for leaks before insulation goes on.
  • Insulate the ducts in unconditioned spaces, and connect them to the furnace or air handler and the registers.
  • Balance the airflow with dampers and check each room's supply and return.

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Every job is different, so we do not publish prices.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 of rooms and registers served, since each run adds fabrication, fittings and labor.
  • Duct material, such as sheet metal, flexible duct or fiberglass board, which changes the labor and fittings.
  • Access to the route, including attic, crawl space, basement and wall cavities.
  • Whether the work needs a new return, which is a larger duct than a typical supply run and needs its own grille and path back to the unit
  • Insulation requirements for ducts in unconditioned spaces.
  • Whether the existing furnace or air handler needs changes to carry the new airflow.
  • Finish work, such as drywall, ceiling or flooring repairs after the ducts go in.

What a written quote should spell out

  • The duct layout, with the number and location of each supply and return.
  • The duct material, sizes and the length of each run, listed by room.
  • Sealing method and the leak test result.
  • Insulation type and its location.
  • Any changes to the furnace, air handler or return grille, listed separately.
  • Warranty terms for the materials and the workmanship.

Questions to ask before you hire

  • How did you size the ducts for each room, and can you show me the calculation?
  • What sealing method do you use on the joints, and will you test for leaks?
  • Will the ducts in the attic or crawl space be insulated, and to what standard?
  • Will you balance the airflow after the install and show me the readings?
  • Does the furnace or air handler need changes to carry the new airflow?
  • Who repairs the drywall, ceilings or floors after the work?
  • Who pulls the permit, and will the new ducts be inspected?

Red flags

  • The pro sizes the new runs by copying existing ducts without checking the airflow.
  • The pro uses cloth duct tape on the joints instead of mastic or foil-backed tape.
  • The pro leaves the ducts in unconditioned spaces without insulation.
  • The quote does not list the sealing or the airflow balancing.

What you can do yourself

You can clear the attic, crawl space or wall access, move stored items, and mark the room layout for the new registers. Keep the work area clean so the installer can reach the duct route. Sizing, sealing, duct fabrication, insulation and balancing belong to a licensed HVAC contractor.

Licenses and permits

Duct installation is commonly done by licensed HVAC contractors, and it may need a permit depending on the work. Check with your state or local licensing agency for the requirements that apply to your job.

Duct installation questions

Why do my rooms have uneven temperatures?

Usually the duct sizes or the airflow balance are off, or the ducts leak or run through hot or cold spaces. A technician measures airflow at each register before deciding on the fix.

Should I use flexible duct or sheet metal?

Each has its place. Sheet metal holds its shape and resists crushing, while flexible duct is easier to route in tight spaces. Ask the installer which parts of the layout suit each.

Do ducts in an attic need insulation?

Generally yes. Ducts in unconditioned spaces need insulation so the heated or cooled air does not lose its temperature on the way to the room.

Can I add a register without adding ductwork?

Sometimes, if the existing duct has spare capacity. A technician should test the airflow first, since adding a register to an undersized run lowers the airflow everywhere else.

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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