Ductwork Cost Calculator

Ducts can cost more than the equipment

A full duct replacement in a 2,000 square foot house typically runs $4,000 to $10,000 — comparable to, and often more than, the air conditioner or furnace it serves. That surprises people who have been quoted $6,000 for a system and assume the ducts are a couple of hundred dollars of pipe. They are not: a duct system is 100 to 250 feet of insulated material, 10 to 15 registers, two or three returns, and a day or two of labour in an attic that is 130°F in July.

The cost is dominated by access, not material. Flex duct costs $12 to $18 a foot installed in an open basement and $20 or more per foot in a finished ceiling where every run means a hole, a patch and a paint touch-up. That is why two quotes for "new ducts" can differ by a factor of two while describing the same house.

Seal first, or replace?

The honest default is to seal before you replace, because the failure mode of most residential duct systems is leakage rather than inadequacy. A typical house loses 20 to 30 percent of its conditioned air to leaks at joints, boots and plenum connections, and that air is being pulled from an attic or a crawlspace. Sealing those joints with mastic — not tape, which fails within a few years — costs $400 to $900 and recovers a large share of that loss.

Replacement is the right answer when the ducts are the wrong size, when they are crushed or disconnected inside a wall, when the insulation has failed and the exterior jacket is gone, or when the layout serves the wrong rooms and no amount of sealing will deliver air to a bedroom that never had a run. A duct blaster test, which pressurises the system and measures leakage in CFM per 100 square feet of floor area, is the diagnostic that separates these cases: a leaky system on an adequate layout gets sealed, and a tight system on a bad layout gets redesigned.

Flex, rigid, or duct board

Flex is cheap, fast and forgiving of misalignment, which is why it dominates residential work. It is also the roughest of the three internally, with 20 to 30 percent more friction than rigid duct of the same nominal size, and it sags: a flex run that droops between hangers has a smaller effective cross-section at the low point and behaves like a smaller duct. Manual D accounts for this with equivalent lengths, which is why a 25 foot flex run with two elbows is treated as considerably more than 25 feet of straight pipe.

Rigid galvanised with an external wrap has the lowest friction and the longest life, and costs 30 to 60 percent more. Duct board sits between: smoother than flex, integrated insulation, and the joints can be sealed with mastic during fabrication. In an attic, the practical difference between R-6 and R-8 is a meaningful heat gain — an R-6 duct in a 130°F attic loses noticeably more cooling than an R-8 one, and R-8 is the usual specification for unconditioned space in modern code.

Returns are the part everyone undersizes

A supply duct that is too small makes a room underperform. A return that is too small makes the whole system underperform, because the blower can only move what the return path allows, and the house ends up pressurised — pushing conditioned air out through the envelope and pulling hot attic air in through every gap. One 20 by 25 return grille for a 3-ton system is a common configuration and it is usually marginal; two smaller returns in different parts of the house are better hydraulically and better for temperature balance.

Return duct is also where the cheapest work happens: adding a return path from a closed-off part of the house, or enlarging a return boot, costs a few hundred dollars and can fix a comfort problem that no equipment change touches.

What a duct quote should state

Linear feet by size, not a lump sum. You are buying a quantity.
R-value of the insulation, and whether it is in unconditioned space.
Whether the design is Manual D or a copy of what was there. Replacing bad ducts with identical bad ducts is a common outcome.
Register and return count, with sizes, and whether they are included in the price.
Sealing method — mastic and mesh, not tape — and whether a leakage test is included.
Drywall and paint: who repairs the holes, and whether that is in the number.

What this estimate leaves out

Drywall repair and paint, which can add $500 to $2,000 in a finished basement or a two-story house with ceiling runs. It also excludes asbestos remediation, which is a real possibility in homes built before about 1980 if the duct insulation is the old grey paper-faced type, and it excludes any structural work needed to create a chase. Those are the items that turn a $6,000 duct job into a $9,000 one after the contract is signed, and they are worth raising before it is.

Frequently asked questions

How much does it cost to replace ductwork in a house?

Most full replacements run $4,000 to $10,000 for a 1,500 to 2,500 square foot house, driven mainly by access and by the number of registers. Flex in an open basement is at the bottom of that range; rigid duct in a finished two-story is at the top.

Is it cheaper to seal ducts or replace them?

Sealing is far cheaper — $400 to $900 against $4,000 or more — and it is the right first step in most houses, because leakage of 20 to 30 percent is the usual problem. Replacement is for ducts that are the wrong size, crushed, or serving the wrong rooms.

How do I know if my ducts leak?

A duct blaster test measures leakage directly, pressurising the system and reporting CFM per 100 square feet of floor area. Without a test, the visible signs are dusty registers, rooms that never reach temperature, and a return that whistles.

Should I use flex or rigid duct?

Flex is cheaper and easier to route, with 20 to 30 percent more friction and a tendency to sag. Rigid has the lowest friction and the longest life at 30 to 60 percent more cost. In an attic, either way, use R-8.

What R-value should attic ducts be?

R-8 is the usual specification for ducts in unconditioned space, and modern code in most climates requires R-8 or better. R-6 was standard for years and loses noticeably more cooling in a 130 degree attic.

Why does my furthest room never get enough air?

Usually because the branch is undersized, the run is long with several elbows, or the return path from that room is restricted. Balancing dampers can help, but if the duct was never sized for the room, no damper will fix it.

Do I need a permit for ductwork?

Usually yes when the system is replaced or substantially altered, and it typically costs $100 to $300. Sealing existing ducts often does not require one, which is another reason to start there.

Disclaimer: This tool estimates ductwork cost from published installed rates. It is not a quote, and it excludes drywall repair, structural changes, asbestos remediation in older duct systems, and any load or duct design work.

Last reviewed: October 30, 2026 · Sources: published 2026 contractor price surveys, ACCA Manual D, IECC duct insulation requirements

Ductwork Cost Calculator