Understanding your result
The headline is the installed cost range, with the length, the material and the midpoint in the sub-line. The stats give the cost per foot, the midpoint and the length. The bars and the table compare the same job in the other material, which shows at a glance how much of the price is the choice of flex or metal. The table also shows the access factor and the source.
If you sized the job by floor area, the length is our estimate and the result is a first look; measuring the runs or using the contractor’s takeoff gives a firmer figure. The per-foot range is wide because it covers everything from a simple branch in an open basement to a large trunk in a tight attic.
Before replacing ducts, find out whether sealing would do: the duct leakage calculator shows what leakage costs a year. New ducts should be sized for the airflow with the duct size calculator and the friction rate from the equivalent length calculator. If the equipment is being replaced at the same time, the replacement cost calculator includes duct options.
How we calculate this
The per-foot ranges are Fixr’s August 2025 installed figures: galvanized sheet metal $21.38 to $62.36 per linear foot, insulated flex $6.75 to $34.19 and uninsulated flex $6.95 to $28.95, rounded. The length estimate and the access and region factors are ours, set out here so they can be checked. Duct sizes, velocities and the friction behind a good layout are on the duct size chart.
The assumptions behind the numbers
| Assumption | Value | Where it comes from |
|---|---|---|
| Sheet metal, installed | $21 to $62 per ft | Fixr, August 2025 |
| Insulated flex, installed | $7 to $29 per ft (Fixr: $6.75 to $34.19) | Fixr, August 2025 |
| Whole-house replacement | $4,000 to $14,000 typical | 2025 ductwork cost guides (Fixr, PickHVAC) |
| Length from area | 0.12 ft per sq ft | Our estimate for trunk-and-branch systems |
| Access factors | 1.0 / 1.2 / 1.5 | Our multipliers |
| Region factors | 0.85 / 1.0 / 1.2 | Our rounding of regional labour differences |
Assumptions last reviewed October 8, 2026.
The calculator does not include removal and disposal of the old ducts, new registers and grilles, drywall repair, asbestos abatement, a Manual D design fee, or a post-installation leakage test, any of which may appear on a quote. The guide to duct leakage and sealing explains when sealing is enough, and the guide to duct sizing basics covers what a good layout looks like.
Two worked examples
A whole house in flex
2,000 sq ft, insulated flex, open basement or easy attic, average-cost area.
- Length: 2,000 × 0.12 = 240 ft
- Cost per foot: $7 to $29
- Total: $1,650 to $7,000, midpoint $4,325
- The same job in sheet metal: $5,000 to $14,900
Flex is the economical choice, and the lower end of the range is realistic only for a simple layout in open space. A metal trunk with flex branches, a common compromise, lands between the two.
A metal trunk in a tight crawl space
120 ft of galvanized sheet metal, tight crawl space, average-cost area.
- Cost per foot: $21 to $62 × 1.2 = $25 to $74
- Total: $3,000 to $8,950, midpoint $5,975
- The same job in flex: $1,000 to $4,200
Crawl-space work costs more per foot because the installer works lying down; the 20% access factor reflects that. Sealing every joint with mastic and insulating the new metal ducts should be in the price.
Where to find your inputs
Length. Measure the trunks and branches in the attic, basement or crawl space, or ask for the contractor’s duct takeoff. Without either, the floor-area estimate is a starting point.
Material. Sheet metal for trunks and long runs; insulated flex for short branches, or throughout on a budget.
Access. Open basement or attic with walking room is easy; a low attic or crawl space is tight; ducts inside finished walls or ceilings are the hardest.
Common mistakes
- Replacing ducts that only need sealing. Test first; sealing costs a fraction.
- Long runs of flex. Friction and sagging starve the far rooms.
- No sealing on new ducts. Every joint needs mastic or UL 181 tape.
- Uninsulated ducts in an attic. They lose heat and sweat in summer.
- Sizing new ducts to the old ones. Size them for the system’s airflow.
- Leaving out returns. Most houses are short of return air; add returns while the ducts are open.
Questions people ask
- How much does ductwork cost per linear foot?
- Fixr's August 2025 guide puts installed galvanized sheet-metal duct at about $21 to $62 per linear foot and insulated flex duct at about $7 to $34, depending on region and complexity. Tight attics and crawl spaces add about 20% in the calculator, and ducts behind finished walls and ceilings about 50%, before drywall repair.
- How much does it cost to replace all the ductwork in a house?
- Whole-house duct replacements typically run $4,000 to $14,000 in 2025 cost guides, with high-end projects over $20,000. A 2,000 sq ft house has roughly 240 ft of duct in a trunk-and-branch system, our estimate, which in flex comes to about $1,650 to $7,000 and in sheet metal about $5,000 to $14,900. Removal of the old ducts, new registers and a Manual D design can be extras.
- Is flex duct or sheet metal better?
- Sheet metal has lower friction, lasts longer, resists damage and can be sealed tightly; it is the better choice for trunks and long runs. Insulated flex is cheaper and faster to install, and fine for short branch runs if it is pulled tight, supported every few feet and not kinked. Most good systems use a metal trunk with short flex branches. Sagging, compressed flex is one of the commonest causes of poor airflow.
- When do ducts need replacing rather than sealing?
- When they are crushed, disconnected, rodent-damaged, uninsulated in an attic, made of old asbestos-wrapped material, or far too small for the system's airflow. Leaky but sound ducts can usually be sealed with mastic or an aerosol sealant for a fraction of the cost of replacement. A duct leakage test and a Manual D check show which you have.
- How much duct does a house have?
- It depends on the layout, but a trunk-and-branch system in a single-storey house typically has 10 to 15 ft of duct per 100 sq ft of floor; the calculator uses 12, so 240 ft for 2,000 sq ft. Two-storey houses with one system and long return runs have more; compact houses with a central air handler less. Measuring the runs in the attic or basement is better than any estimate.
- Does new ductwork include sealing and insulation?
- It should. Ducts in unconditioned space need insulation (R-8 is the usual code minimum in attics) and every joint should be sealed with mastic or UL 181-rated tape, not cloth duct tape. Insulated flex comes with its insulation; sheet metal in an attic must be wrapped. Ask the contractor to state the sealing method and the insulation R-value on the quote, and to test leakage after installation.