Ductwork replacement and sealing in Dallas

Why ducts matter in Dallas

Many Dallas homes run ducts through the attic, which is the hottest place in the house in summer. Leaks there pull in attic air and waste cooling the new system paid for.

ENERGY STAR estimates that about 20 to 30 percent of the air moving through a typical duct system is lost to leaks, holes and poorly connected ducts. That loss happens before the air reaches a single room. A new high-efficiency AC on leaky attic ducts still delivers only what survives the trip.

DFW averages 20 days a year at or above 100 °F on the 1991–2020 normals, two more than on the 1981–2010 normals. Those are the afternoons when attic ducts gain the most heat and leaks cost the most. ENERGY STAR material states that nearly half of heating and cooling equipment in US homes never performs to its advertised capacity and efficiency because of installation problems. Ducts are a large part of that installation picture.

Signs of duct problems

ENERGY STAR lists these as signs of poorly performing ducts. Any one is a reason to ask for a duct inspection with an AC quote.

• High summer and winter utility bills.
• Rooms that are hard to heat or cool.
• Stuffy rooms that never feel comfortable.
• Ducts located in an attic, crawlspace or garage.
• Tangled or kinked flexible ducts.

Things you can check yourself from the attic hatch, carefully and in cool weather: flex duct lying crushed under storage, runs that have pulled off a register box or plenum, sagging runs with sharp bends, and torn outer jackets on insulated flex duct. Dust streaks around ceiling registers can also point to gaps at the boot. Do not walk on attic drywall; step only on framing.

Room-by-room trouble deserves its own diagnosis. The rooms that never cool guide covers causes that are not ducts, such as windows, insulation and sizing.

Cost

Published third-party ranges, not this site's prices. Each row keeps its geography.

Why the Dallas sealing band is wide: at the low end it covers sealing joints and boots on sound ducts; at the high end it shades into replacing sections. What moves the price:

• Attic access. Low roof pitch, deep insulation and stored items slow the work.
• Number of runs. Each supply and return run has joints at both ends.
• Material. Sheet-metal trunks and flex branches are sealed differently.
• Testing. A before-and-after leakage test adds time but proves the result.

The full AC installation cost guide shows how these adders sit on top of the equipment price.

Worked examples

The scenarios below are hypothetical, built from the published ranges above to show the decision, not to predict a quote.

Sound ducts, leaky joints

Say a 1990s Dallas house is replacing a 3-ton AC. The ducts are metal trunks with flex branches, in good shape, but the installer finds open seams at the plenum and gaps at several boots. Sealing sits toward the lower end of the published Dallas band of $1,300–$8,000, and it is done while the installer is already in the attic.

Crushed, aging flex duct

Say an older house has flex duct with torn jackets, several runs flattened by storage, and one run disconnected. Sealing will not fix crushed or torn ducts. New ductwork for about 2,000 square feet is published in Dallas at $6,000–$7,000, from an undated page, so treat it as indicative and get a written quote.

One room too warm

Say only one back bedroom struggles. Before pricing a whole-house job, ask the contractor to inspect that run for kinks, a disconnected boot or an undersized branch. A single-run fix can be far cheaper. If no duct can reach the room well, a ductless mini-split is the alternative.

Seal or replace

• Seal when the ducts are sound and the right size but leak at joints and boots.
• Replace when they are crushed, torn, badly undersized for the new system, or old flex duct past its life.

Size matters most when the new system differs from the old one. Ask whether the ducts can carry the airflow the new equipment needs; undersized ducts cause noise and weak airflow at the far registers.

Testing the ducts

A duct leakage test pressurizes the duct system with a calibrated fan and measures how much air escapes. Done before and after sealing, it shows whether the work helped. Ask whether the contractor tests, what equipment they use, and whether you will get both numbers in writing.

A visual inspection is better than nothing, but it misses leaks inside walls and chases. If a contractor recommends full replacement without testing, ask what evidence the recommendation rests on.

Airflow at the registers is a separate check. A contractor can measure it room by room to show whether a run is undersized or blocked, which leakage testing alone does not reveal.

What good sealing looks like

ENERGY STAR recommends sealing air leaks with mastic sealant or metal tape, and avoiding duct tape, which does not last. It points to the connections at vents and registers, where they meet floors, walls and ceilings, as common leak spots.

1. Seal the plenum and trunk joints at the air handler, where pressure is highest.
2. Seal every branch takeoff and boot, including where the boot meets the ceiling drywall.
3. Reconnect and strap loose runs so they cannot pull apart again.
4. Insulate. ENERGY STAR advises insulating all accessible ducts in attics, crawlspaces and garages.
5. Re-test and record the result.

Aerosol sealing from the inside is another method some contractors offer. Ask what it seals, what it cannot reach, and whether the result is tested.

What replacement involves

Full replacement means removing old trunks and flex runs, installing new ones sized for the system, sealing and insulating every joint, and reconnecting each register. Partial replacement does the same for the damaged runs only.

• Design. Ask whether the new layout is designed from the room loads (the ACCA method is Manual D) or copied from the old one.
• Returns. Too few returns starve the system of air. Ask how many returns the new layout has and where.
• Flex runs. Long, sagging or sharply bent flex runs restrict airflow. Ask how runs will be supported and kept short.
• Old ducts. Ask whether removal and disposal are in the price.

Timing with a new AC

The best time to deal with ducts is during an AC replacement. The installer is already in the attic, the system is off, and the duct work can be sized for the new equipment. Duct work bolted onto the end of a job, after the equipment is set, tends to be rushed.

Ask for duct work as a separate, itemized line on every quote, so you can compare like with like. Our guide to what happens during an AC replacement shows where duct work fits in the day.

Return air and filters

Supply ducts get most of the attention, but the return side matters as much. Return ducts carry room air back to the system. If they leak in the attic, the system pulls in hot, dusty attic air instead of house air, which adds load and dirt to the coil.

Common return problems in older Dallas houses:

• One central return for the whole house. Closed bedroom doors then starve the system and pressurize those rooms; ask whether jumper ducts or transfer grilles would help.
• A leaky return plenum or filter box at the air handler, often in the attic or a closet.
• An undersized return grille, which is noisy and restricts airflow.
• A filter that does not fit its slot, letting air bypass it.

Ask the contractor to inspect and seal the return side with the supply side, and to confirm the filter size and location. A filter that is hard to reach tends not to get changed, so ask where it will be after the job.

A clean filter on sealed returns is one of the cheapest ways to protect a new coil. Check it monthly in summer and change it when it looks dirty.

Common mistakes

• Buying a bigger AC to fix a duct problem. More capacity through leaky or crushed ducts still misses the rooms that need it, and can cause short cycling. See oversized AC problems.
• Sealing with duct tape. ENERGY STAR says it does not last.
• Sealing without insulating. Sealed but bare ducts in a Dallas attic still gain heat.
• No test. Without before-and-after numbers you cannot tell whether the sealing worked.
• Confusing cleaning with sealing. They are different jobs.
• Comparing quotes that differ on duct scope. One quote with duct work and one without are not comparable.

What to ask

• Will you test the ducts for leakage, before and after?
• Are the ducts sized for the new system's airflow?
• Is duct work in the quote, or a separate line?
• What will you seal with, and will you insulate the ducts afterward?
• Which runs, if any, need replacing, and why?
• How many returns will the system have?
• Is removal of old ducts included?

Put the answers side by side in the quote comparison tool.

Sources

• Budget Heating, AC replacement cost in Dallas (Dallas, page dated undated) (retrieved 2026-10-20)
• HVAC.com, HVAC replacement costs in Dallas, TX (Dallas, page dated 2024-05-22) (retrieved 2026-10-20)
• PickHVAC, duct repair and sealing cost (National, page dated 2026-05-26) (retrieved 2026-10-20)
• ENERGY STAR, "Duct Sealing" (retrieved 2026-10-20)
• ENERGY STAR, Duct Sealing (retrieved 2026-10-20)
• ENERGY STAR HVAC fact sheet (retrieved 2026-10-20) — verify before relying on it
• NWS Fort Worth, "1991–2020 Normals" (retrieved 2026-10-20)

Questions

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