Ductwork replacement in Southern Maryland costs $1,400 to $5,600 in 2026, with most homeowners in Calvert, St. Mary's, and Charles County paying $2,500 to $5,000 for a full or partial duct system replacement. That price includes materials, labor, connections to the existing HVAC equipment, sealing, and basic insulation. Minor duct repairs, patching a disconnected joint, sealing a few leaky seams, run $200 to $700. A full duct system replacement for a large home over 3,000 square feet can reach $9,000 or more depending on the layout, material choice, and accessibility of the ductwork.
The range is wide because duct replacement costs depend on the size of the home, the type and length of duct material used, where the ducts are located (crawl space, attic, or basement), the complexity of the layout, and how much of the system needs to be replaced versus repaired. A home that needs four new duct runs to bedrooms is a different project than a home that needs every inch of ductwork in a 40-year-old crawl space torn out and rebuilt.
Fall is a smart time to address ductwork in Southern Maryland. Heating season starts in earnest by late October, and a leaking or deteriorated duct system means your furnace or heat pump is pushing heated air into your crawl space, attic, or wall cavities instead of into your living rooms. The Department of Energy estimates that the average home loses 20 to 30 percent of conditioned air through duct leaks and poor connections, that is 20 to 30 cents of every dollar you spend on heating and cooling going into spaces you do not live in. In the tri-county area, where summers push into the mid-90s with crushing humidity and winters drop into the 20s, that wasted energy adds up fast.
Southern Maryland's climate creates specific problems for ductwork that homeowners in drier regions do not face. The Chesapeake Bay watershed environment means sustained summer humidity that causes condensation on uninsulated or poorly insulated duct surfaces, especially ducts running through unconditioned crawl spaces and attics. That condensation leads to mold growth on and inside the ducts, degraded insulation, and rust on sheet metal components. If your ducts are in a vented crawl space (common in homes built before 2000 in Calvert, Charles, and St. Mary's counties), the combination of ground moisture, humid outside air, and cool duct surfaces creates ideal conditions for condensation and biological growth.
Here is what ductwork replacement and repair actually costs in Southern Maryland, what drives the price, and how to know when your ducts need attention.
Ductwork Replacement Cost by Home Size
The size of the home is the primary cost driver because it determines how many duct runs are needed and how much material the job requires. Larger homes need more supply runs, longer trunk lines, and more return air capacity.
| Home Size (sq ft) | Typical Duct Replacement Cost | Notes |
|---|---|---|
| 1,000 to 1,500 | $1,400 to $3,400 | Small rancher or Cape Cod; shorter runs, simpler layout |
| 1,500 to 2,000 | $2,100 to $4,500 | Average 3-bedroom home; the most common project size in the tri-county area |
| 2,000 to 2,500 | $2,800 to $5,600 | Larger colonial or split-level; multiple zones likely |
| 2,500 to 3,000 | $3,500 to $6,700 | Large home; may require multiple trunk lines or zoned system |
| 3,000+ | $4,200 to $9,000+ | Estate-size or multi-level; complex layouts, long runs, possibly multiple HVAC systems |
Most homes in Waldorf, La Plata, Prince Frederick, Leonardtown, and Lexington Park fall in the 1,500 to 2,500 square foot range. The typical full duct replacement for a 2,000-square-foot home with ducts in the crawl space or attic runs $2,800 to $4,500, that is the number most Southern Maryland homeowners should plan around.
Cost Per Linear Foot and Per Duct Run
Contractors price ductwork by the linear foot of material installed or by the individual duct run (a single line from the trunk to a register). Both methods are common, and understanding the per-unit costs helps you evaluate quotes.
| Pricing Method | Cost Range | What It Includes |
|---|---|---|
| Per linear foot (installed) | $25 to $55 | Material, hangers, connections, basic sealing |
| Per duct run (supply or return) | $270 to $500 | Complete run from trunk to register, including boot, register, and connections |
A typical 2,000-square-foot home has 8 to 14 supply runs and 2 to 4 return runs. Each supply run averages 15 to 25 feet depending on the distance from the trunk line to the room. The total linear footage of ductwork in a typical system is 200 to 400 feet when you include the trunk line, branches, and return air paths.
Duct Material Costs
The material you choose affects both the upfront cost and the long-term performance of the system. Each material has a different cost per linear foot and different trade-offs for durability, airflow efficiency, and resistance to Southern Maryland's humid conditions.
| Material | Cost Per Linear Foot (Material Only) | Installed Cost Per Linear Foot | Best For | Lifespan |
|---|---|---|---|---|
| Flex duct (non-insulated) | $1 to $3 | $25 to $35 | Short runs in conditioned spaces; budget projects | 10 to 15 years |
| Flex duct (insulated) | $2 to $4 | $28 to $40 | Attic and crawl space runs; most residential replacements | 15 to 25 years |
| Fiberboard duct | $4 to $6 | $30 to $45 | Trunk lines and main branches; good insulation value | 15 to 20 years |
| Sheet metal (galvanized steel) | $7 to $13 | $35 to $55 | Trunk lines, high-airflow runs, commercial-grade residential systems | 25 to 30+ years |
Flex Duct
Flexible duct, a wire-coil inner liner surrounded by insulation and an outer vapor barrier, is the most commonly installed duct material in residential Southern Maryland. It is lightweight, easy to route through crawl spaces and attics, and the least expensive option. The insulated version (R-4.2 to R-8.0 insulation value) is standard for any run through an unconditioned space.
The downside of flex duct is airflow restriction. The corrugated interior surface creates more friction than smooth sheet metal, which means the blower has to work harder to push the same volume of air. This matters most on long runs (over 25 feet) and when the flex duct is not pulled taut, sagging, kinked, or compressed flex duct can reduce airflow by 20 to 40 percent. Proper installation, fully stretched, supported by hangers every 4 to 5 feet, with smooth, gradual bends rather than sharp kinks, is critical. A lot of the duct problems we see in Southern Maryland homes are not bad duct material but bad duct installation: flex duct draped over framing members, crushed under insulation, or looped in excess coils because the installer cut it too long and did not bother to trim it.
Fiberboard Duct
Fiberboard duct is made from compressed fiberglass with a foil-faced exterior. It has built-in insulation (typically R-4.3 to R-6.5), cuts cleanly with a knife, and assembles with mastic and foil tape. It is commonly used for trunk lines and main branches where a rigid, well-insulated duct is needed. Fiberboard is quieter than sheet metal because the fiberglass absorbs sound.
The concern with fiberboard in Southern Maryland is moisture. If the outer foil facing is damaged or the joints are not properly sealed, humidity can penetrate the fiberglass core. Wet fiberglass insulation loses its insulation value and becomes a growth medium for mold. In a vented crawl space with high humidity, damaged fiberboard duct can develop significant mold contamination inside the duct wall, a problem that is not visible from the outside and that cannot be cleaned, only replaced.
Sheet Metal
Galvanized sheet metal is the most durable duct material and delivers the best airflow performance. The smooth interior surface creates minimal friction loss, the material does not sag or compress, and it is impervious to moisture penetration. Sheet metal ducts last 25 to 30 years or more, often the life of the home.
The higher cost reflects both the material and the labor. Sheet metal ducts are fabricated in a shop (or on-site by a skilled sheet metal worker) and assembled with screws, mastic, and foil tape. The installation is more labor-intensive than flex duct. For trunk lines and critical high-volume runs, sheet metal is the best investment. Many contractors in the tri-county area use a hybrid approach: sheet metal for the trunk line and main branches, insulated flex duct for the individual supply runs to each room. This balances cost and performance.
Ductwork Replacement Cost by Location
Where your ducts are located in the house significantly affects the replacement cost. Accessibility drives labor time, and labor is the largest single cost component in a duct replacement.
| Duct Location | Replacement Cost Range | Why It Costs More or Less |
|---|---|---|
| Crawl space | $3,000 to $7,300 | Limited headroom (18 to 36 inches in most Southern Maryland crawl spaces); difficult access; moisture and mold concerns often require extra prep work |
| Attic | $2,200 to $5,600 | Heat exposure in summer; insulation must be moved and replaced; access through scuttle holes or pull-down stairs limits material staging |
| Basement (unfinished) | $1,800 to $3,100 | Easiest access, full standing height, open framing, visible connections; shortest labor time |
| Basement (finished) | $3,000 to $5,500 | Soffits and drywall must be opened and repaired; adds carpentry and drywall cost |
| Walls and chases (enclosed) | $4,000 to $8,000+ | Ductwork buried in walls or framing chases; requires opening and repairing finished surfaces; often the most expensive scenario |
Crawl Space Ductwork in Southern Maryland
Crawl space duct replacement is the most common and the most problematic job in the tri-county area. A large percentage of homes in Calvert, Charles, and St. Mary's counties, especially those built from the 1960s through the 1990s, have HVAC systems with ductwork running through vented crawl spaces. These crawl spaces are typically 18 to 36 inches high, have dirt or gravel floors, and in many cases have standing water or saturated soil during wet seasons.
The combination of humid outside air entering through foundation vents, ground moisture rising from the soil, and cool conditioned air inside the ducts creates persistent condensation on duct surfaces. Over 15 to 25 years, this condensation degrades insulation wraps, corrodes sheet metal connectors, and promotes mold growth on and inside the duct system. Many homeowners in Mechanicsville, Hollywood, Lusby, California, Chesapeake Beach, and other tri-county communities discover their duct problems during a home inspection, a mold assessment, or simply by crawling under the house and finding ducts that are sagging, disconnected, wrapped in soaked insulation, or visibly moldy.
If your crawl space ducts are being replaced, it is worth evaluating the crawl space itself. A duct replacement in a wet, vented crawl space solves today's problem but puts the new ducts in the same environment that destroyed the old ones. Crawl space encapsulation, sealing the vents, installing a vapor barrier over the floor, and conditioning the space with a dehumidifier or supply air, costs $5,000 to $15,000 but protects the new ductwork (and the floor framing, insulation, and everything else in the crawl space) for decades. Many homeowners combine duct replacement with crawl space encapsulation for the best long-term result.
Duct Repair and Sealing Costs
Not every duct problem requires a full replacement. If the duct system is structurally sound but has leaks, disconnected joints, or damaged insulation, repair and sealing can restore performance at a fraction of replacement cost.
| Repair Type | Cost Range | What It Addresses |
|---|---|---|
| Minor repair (patch, reconnect, reseal a few joints) | $200 to $700 | Disconnected flex duct, torn outer jacket, failed tape at a connection |
| Duct cleaning (full system) | $300 to $700 | Dust, debris, pet dander, and light biological growth inside the ducts |
| Manual duct sealing (mastic and tape, accessible joints) | $400 to $1,900 | Sealing leaks at joints, boots, takeoffs, and trunk connections by hand |
| Aeroseal duct sealing | $1,300 to $2,700 | Sealing leaks from the inside using aerosolized sealant; reaches joints that are inaccessible for manual sealing |
| Duct insulation (add or replace) | $800 to $2,000 | Adding insulation wrap to uninsulated ducts or replacing degraded insulation |
| Adding a new vent / register | $250 to $500 | Running a new branch duct from the trunk line to a room that needs better airflow |
Manual Sealing vs. Aeroseal
Manual sealing involves a technician physically accessing each duct joint, connection, and seam and applying mastic (a thick, non-hardening sealant) and UL-listed foil tape. This works well when the ductwork is accessible, exposed in a basement, or reachable in a crawl space or attic. The cost depends on how many connections need sealing and how accessible they are.
Aeroseal is a technology that seals ducts from the inside. The technician temporarily blocks all registers, pressurizes the duct system, and injects an aerosolized polymer sealant into the pressurized ducts. The sealant particles are carried by the escaping air to the leak points, where they accumulate and seal the gaps. Aeroseal can seal leaks in ductwork that is completely inaccessible, inside walls, above ceilings, in chases that cannot be opened. It is effective on leaks up to about 5/8 inch in diameter.
The cost is higher ($1,300 to $2,700 versus $400 to $1,900 for manual sealing), but Aeroseal reaches leaks that manual sealing cannot. For homes with ductwork partially buried in finished walls or ceilings, common in two-story homes in Waldorf, Dunkirk, and the planned communities around Lexington Park, Aeroseal often provides a better result than manual sealing alone.
When to Repair vs. Replace
Repair makes sense when: - The duct system is less than 15 years old and structurally sound - The problem is localized, a few disconnected runs, some failed tape, or isolated damage - The duct material is in good condition (no rust on sheet metal, no crushed or permanently kinked flex duct, no moisture-damaged fiberboard) - Sealing and insulating the existing system can bring performance to acceptable levels
Replace when: - The duct system is over 20 years old and showing widespread deterioration - Flex duct is sagging, crushed, kinked in multiple locations, or has degraded insulation and outer jackets - Sheet metal trunk lines have significant rust, holes, or failed joints - Fiberboard ducts show moisture damage, delamination, or mold growth inside the duct wall - The system was poorly designed originally, undersized trunk lines, inadequate return air, excessive duct runs with too many bends - You are replacing the HVAC equipment and the existing ducts are not compatible with the new system's airflow requirements
Permit Requirements in Southern Maryland
Ductwork replacement in Calvert, Charles, and St. Mary's counties typically requires a mechanical permit. The permit ensures the installation meets the current Maryland Mechanical Code (based on the International Mechanical Code) for duct sizing, materials, sealing, insulation, and clearances.
| County | Permit Cost | Issuing Office | Notes |
|---|---|---|---|
| Calvert County | $50 to $200 | Department of Planning & Zoning | Permit required for new duct installation and full system replacement; minor repairs may be exempt, check with the office |
| Charles County | $50 to $175 | Department of Planning & Growth Management | Mechanical permits cover HVAC-related ductwork; plan review may be required for new duct layouts |
| St. Mary's County | $50 to $250 | Department of Land Use & Growth Management | Permit required for duct system replacement; additional review for homes in the Critical Area near the Chesapeake Bay or its tributaries |
A licensed HVAC contractor handles the permit process as part of the project. The permit typically costs $50 to $250, a small fraction of the total job cost. An inspection after the work is completed verifies that the installation meets code. Common inspection items include proper duct support, sealed and insulated joints, correct material types, adequate clearances from combustible materials, and proper connections to the air handler or furnace.
Do not skip the permit. Unpermitted HVAC work can void your homeowner's insurance coverage for related claims, create problems during a home sale (the home inspection will flag unpermitted modifications), and result in fines if discovered by the county. A quality contractor insists on permitting because it protects both the homeowner and the contractor.
What Drives Ductwork Cost in Southern Maryland
Accessibility
The single biggest labor cost variable. Replacing ducts in a full-height basement with open joists takes half the time of the same job in a 24-inch crawl space where the technician is working on their stomach. Attic work in July, when Southern Maryland attic temperatures exceed 130 degrees, requires early-morning scheduling, frequent breaks, and additional safety precautions, all of which extend the project timeline.
Duct System Complexity
A simple ranch home with a central furnace and 8 supply runs is a different project than a two-story colonial with 16 supply runs, 4 return runs, a zoned system with motorized dampers, and ductwork that transitions from the basement through floor and wall chases to the second floor. More runs, more connections, more transitions, and more zones all increase cost.
Mold Remediation
If existing ductwork has mold contamination, common in crawl spaces throughout Calvert, Charles, and St. Mary's counties, the old ducts must be carefully removed and disposed of to prevent spreading mold spores through the home. Some situations require professional mold remediation before new ducts are installed, especially if the mold has spread to the framing, subfloor, or insulation around the ducts. Mold remediation adds $500 to $3,000 or more to the project depending on the extent of contamination.
HVAC System Compatibility
If you are replacing ductwork as part of an HVAC system upgrade, new furnace, new heat pump, or a switch from one system type to another, the new ductwork must be sized for the new equipment's airflow requirements. A new high-efficiency heat pump may need larger return air ducts than the old system had, or a new variable-speed air handler may require differently sized supply runs to deliver the right airflow to each room. Designing a new duct layout rather than replicating the old one adds engineering time and may change the scope of the project.
Insulation Requirements
Ducts in unconditioned spaces, crawl spaces, attics, and unheated garages, must be insulated to prevent energy loss and condensation. The current energy code for Southern Maryland (Climate Zone 4A) requires a minimum of R-8 insulation on supply ducts and R-6 on return ducts in unconditioned spaces. If your existing ducts have no insulation or degraded insulation, the replacement project must include insulation that meets current code.
For the Southern Maryland climate specifically, R-8 insulation on supply ducts running through a hot attic or a humid crawl space is the practical minimum. In attics where summer temperatures exceed 130 degrees, the temperature differential between the 55-degree supply air inside the duct and the 130-degree air surrounding the duct is enormous, 75 degrees. Without adequate insulation, that supply air arrives at the register 10 to 15 degrees warmer than it left the air handler, which means your air conditioning system works harder and runs longer to cool the house.
Sample Project Costs: Three Scenarios
Scenario 1: Partial Duct Replacement in a Crawl Space Ranch
A homeowner in Mechanicsville has a 1,600-square-foot ranch built in 1985 with flex ductwork in a vented crawl space. A home energy audit revealed that three of the eight supply runs are disconnected or severely damaged, the trunk line insulation is degraded, and duct leakage is measured at 35 percent (more than three times the acceptable threshold). The homeowner opts to replace the three damaged supply runs, add insulation to the trunk line, and seal all accessible joints.
| Component | Cost |
|---|---|
| Remove 3 damaged flex duct runs | $150 to $300 |
| Install 3 new insulated flex duct runs (avg 20 ft each, 60 ft total at $28 to $40/ft) | $1,680 to $2,400 |
| New register boots and grilles (3) | $90 to $180 |
| Trunk line insulation wrap (40 linear ft at $5 to $8/ft) | $200 to $320 |
| Manual duct sealing, mastic and foil tape on all accessible joints | $400 to $800 |
| Permit (St. Mary's County) | $50 to $150 |
| Total | $2,570 to $4,150 |
This partial replacement addresses the most severe problems without the cost of a full system replacement. It is a practical approach when the trunk line and the majority of the duct runs are still in serviceable condition. The duct sealing on the remaining runs closes the leaks that are wasting energy, and the new insulation on the trunk line reduces condensation and heat loss.
Scenario 2: Full Duct Replacement in a Two-Story Colonial
A homeowner in Waldorf has a 2,400-square-foot two-story colonial built in 1992. The HVAC technician who serviced the system this summer reported that the original ductwork, a mix of sheet metal trunk lines and flex duct branches, is at the end of its useful life. The flex duct in the crawl space is sagging, kinked, and has moisture-damaged insulation. The sheet metal trunk has multiple rusted seams. The homeowner decides to replace the entire duct system while also upgrading from a single-zone to a two-zone layout (first floor and second floor).
| Component | Cost |
|---|---|
| Remove entire existing duct system | $400 to $800 |
| New sheet metal trunk line and main branches (80 ft at $35 to $55/ft) | $2,800 to $4,400 |
| New insulated flex duct supply runs (12 runs, avg 20 ft each, 240 ft at $28 to $40/ft) | $6,720 to $9,600 |
| New return air ducts and plenums (4 returns) | $800 to $1,600 |
| Register boots, grilles, and transitions (16 total) | $320 to $640 |
| Two-zone damper system with thermostat wiring | $800 to $1,500 |
| Duct sealing, mastic and foil tape on all joints | $400 to $800 |
| Crawl space cleanup (old insulation and debris removal) | $300 to $600 |
| Permit (Charles County) | $50 to $175 |
| Total | $12,590 to $20,115 |
This is a comprehensive project that goes beyond a simple duct replacement, the addition of zoning adds cost but dramatically improves comfort in a two-story home. Two-story colonials in the Waldorf, White Plains, and La Plata area are notorious for the second floor being 5 to 10 degrees warmer than the first floor in summer. A properly designed two-zone system with dedicated return air on each floor eliminates that temperature imbalance.
Note that this project is at the higher end because of the zoning addition and the hybrid sheet metal/flex duct approach. A simpler full replacement of the same home using all insulated flex duct and maintaining the single-zone layout would run $4,200 to $7,500.
Scenario 3: Attic Ductwork Replacement in a Cape Cod
A homeowner in Lusby has a 1,800-square-foot Cape Cod with a second-floor bonus room and two bedrooms served by ductwork running through the attic. The attic ductwork is original to the 2001 construction, insulated flex duct that has been baking in attic heat for 25 summers. The insulation is compressed and degraded, several connections have pulled apart, and the bonus room duct is crushed under blown-in insulation that was added later without protecting the ducts. The homeowner is replacing the attic ductwork only; the first-floor ducts in the crawl space are in good condition.
| Component | Cost |
|---|---|
| Remove existing attic ductwork (6 runs plus trunk) | $300 to $500 |
| Move and replace blown-in insulation around duct area | $400 to $800 |
| New insulated flex duct runs (6 runs, avg 18 ft each, 108 ft at $30 to $42/ft) | $3,240 to $4,536 |
| New rigid fiberboard trunk section (20 ft at $30 to $45/ft) | $600 to $900 |
| Register boots, grilles, and connections (6) | $150 to $300 |
| Duct sealing, all joints and connections | $250 to $500 |
| Permit (Calvert County) | $50 to $200 |
| Total | $4,990 to $7,736 |
Attic duct replacement in Southern Maryland has a seasonal timing consideration. The work should be scheduled for fall, winter, or early spring, not midsummer. Attic temperatures in Calvert, Charles, and St. Mary's counties regularly exceed 130 degrees from June through August. Working in those conditions is unsafe for extended periods, and most contractors either refuse attic work during peak summer or schedule it for early-morning hours only, which extends the project timeline and can increase cost. Booking the work for October or November means cooler attic temperatures, faster installation, and often better contractor availability.
Signs Your Ductwork Needs Replacement
Ductwork does not fail dramatically, there is no flood or power outage to announce the problem. Duct deterioration is gradual, and most homeowners live with the symptoms for years without connecting them to the duct system.
Uneven temperatures room to room. If some rooms are comfortable while others are always too warm or too cold, the most common cause is ductwork problems, a disconnected or crushed duct to the uncomfortable room, a duct run that is too long or has too many bends, or a trunk line that is undersized for the system. Before concluding that your HVAC system is too small or too old, have the ductwork inspected.
High energy bills relative to neighbors. If your heating and cooling costs are significantly higher than similar-sized homes in your area, duct leakage is a likely contributor. A duct system leaking 25 to 30 percent of its conditioned air forces the HVAC system to run 25 to 30 percent longer to maintain the same temperature, that is a direct increase in your electricity or propane bill.
Excessive dust. If your home seems unusually dusty no matter how often you clean, leaky return air ducts may be pulling unfiltered air from the crawl space, attic, or wall cavities into the system and distributing it throughout the house. This is not just a cleanliness issue, crawl space air can contain mold spores, insulation fibers, rodent droppings, and soil particles.
Musty or stale odors from the registers. Mold growth inside the ducts or on the exterior insulation produces a musty smell that is distributed through the house every time the system runs. This is particularly common in homes with crawl space ductwork in the humid tri-county area.
Visible damage. If you can see your ducts, in the basement, crawl space, or attic, look for sagging flex duct, disconnected joints, torn or missing insulation wrap, rust on sheet metal sections, water stains, and visible mold. Any of these indicate a duct system that is not performing as intended.
Age. Flex duct installed 20 or more years ago is at or past its expected service life. The inner liner becomes brittle, the wire coils lose tension and allow the duct to collapse, and the insulation and vapor barrier degrade. Sheet metal lasts longer but is not immune, rust, failed joints, and deteriorated sealant accumulate over decades.
Noise. Rattling, popping, or whistling from the duct system indicates loose connections, undersized ducts, or air velocity problems. While noise alone does not always mean replacement is needed, it often signals issues that a duct inspection should evaluate.
Energy Savings from Duct Replacement
A properly sealed and insulated duct system delivers measurable energy savings. In Southern Maryland's climate, heating degree days around 4,200 and cooling degree days around 1,500, HVAC systems run a significant portion of the year. The savings from eliminating duct losses are real and ongoing.
| Duct System Condition | Estimated Annual Energy Loss | Estimated Annual Cost of Duct Losses (avg Southern MD home) |
|---|---|---|
| Well-sealed, properly insulated (less than 5% leakage) | Minimal | $50 to $100 |
| Moderate leaks and fair insulation (10 to 15% leakage) | Noticeable | $200 to $400 |
| Significant leaks and poor insulation (20 to 30% leakage) | Substantial | $400 to $800 |
| Severely deteriorated (30%+ leakage, disconnected runs) | Extreme | $600 to $1,200+ |
A home with severely deteriorated ductwork that replaces the system with properly sealed and insulated new ducts can reduce heating and cooling costs by $400 to $800 per year. Over the 20-year lifespan of a quality duct installation, that is $8,000 to $16,000 in energy savings, far more than the replacement cost. The payback period for a full duct replacement in a home with badly leaking ducts is typically 3 to 7 years.
Beyond energy savings, new ductwork improves comfort (even temperatures, better airflow), indoor air quality (sealed system pulls less unfiltered air), and HVAC equipment lifespan (the system runs less because it is not fighting duct losses).
Frequently Asked Questions
How much does it cost to replace ductwork in Southern Maryland? Most homeowners pay $2,500 to $5,000 for a full or partial duct replacement. The full range is $1,400 to $5,600 for standard homes, with larger or more complex projects reaching $6,700 to $9,000 or more. The cost depends on home size, duct material, accessibility (crawl space, attic, or basement), and how much of the system needs replacement.
How long does ductwork last? Flex duct typically lasts 15 to 25 years with proper installation and favorable conditions. In Southern Maryland's humid crawl spaces and hot attics, 15 to 20 years is more realistic. Sheet metal ducts last 25 to 30 years or more. Fiberboard ducts last 15 to 20 years but are vulnerable to moisture damage, which can shorten their life significantly in high-humidity environments.
Can I replace just part of my ductwork? Yes. Partial replacement is common and cost-effective when some sections of the system are damaged while others are in good condition. Replacing three or four failed runs while sealing and insulating the rest of the system can restore performance without the cost of a full replacement. A duct inspection identifies which sections need replacement and which can be repaired.
How do I know if my ducts are leaking? A duct leakage test (also called a duct blaster test) measures the total leakage in the system by pressurizing the ducts and measuring the airflow needed to maintain that pressure. An HVAC contractor or energy auditor performs this test, which costs $150 to $300. The result is expressed as a percentage of total system airflow, less than 5 percent leakage is excellent, 5 to 10 percent is acceptable, and anything over 15 percent indicates a sealing or replacement need.
Is duct cleaning worth it? Duct cleaning ($300 to $700 for a full system) makes sense if you can see dust buildup inside the ducts, if there are visible signs of mold or biological growth, if someone in the household has allergies or respiratory issues that worsen when the system runs, or if the home has had recent construction or renovation that introduced dust into the system. Routine duct cleaning every 3 to 5 years is reasonable in Southern Maryland given the humidity and the prevalence of pollen, mold spores, and dust in the local environment. Duct cleaning does not fix leaky, damaged, or poorly insulated ducts, it only cleans the interior surfaces.
What is Aeroseal and is it worth the cost? Aeroseal is an interior duct sealing technology that injects aerosolized sealant into the pressurized duct system, sealing leaks from the inside. It costs $1,300 to $2,700 and is most valuable when ductwork is partially inaccessible, inside walls, above finished ceilings, or in tight chases. For ducts that are fully accessible in a basement or crawl space, manual sealing with mastic and tape ($400 to $1,900) is typically more cost-effective. Aeroseal is worth the premium when manual access to the leaks is not possible.
Do I need a permit to replace ductwork? Yes, in most cases. Calvert, Charles, and St. Mary's counties require a mechanical permit for duct system replacement. The permit fee is $50 to $250 depending on the county and the scope of work. Your contractor should pull the permit and schedule the post-installation inspection as part of the project.
Should I replace ductwork at the same time as my HVAC system? If your ductwork is over 15 years old and you are replacing your furnace, heat pump, or air handler, replacing the ducts at the same time is often the best value. The contractor is already on-site, the duct connections are already being opened, and the new ductwork can be properly sized for the new equipment's airflow requirements. A new high-efficiency HVAC system connected to old, leaky ductwork will never deliver its rated efficiency, you will pay for high-efficiency equipment but get low-efficiency performance.
How long does duct replacement take? A partial replacement (3 to 6 runs) takes 1 to 2 days. A full system replacement for a standard home takes 2 to 4 days. Larger or more complex projects, homes with ductwork in multiple locations, zoned systems, or limited access, may take 4 to 5 days. Add 1 to 3 weeks for the permit approval process before work begins.
Concerned about your ductwork, or planning an HVAC upgrade and wondering about the ducts? Gray & Sons Contracting has been serving Southern Maryland for 50 years. We inspect, repair, and replace ductwork throughout Calvert, St. Mary's, and Charles County, from crawl space flex duct replacements in Mechanicsville to full system upgrades in Waldorf to attic duct work in Lusby and Solomons. We know the local climate, the local building codes, and the specific challenges that humidity, condensation, and coastal-area conditions create for ductwork in this region. Get a Free Estimate