While newer homes are constructed to modern energy efficiency standards, older homes commonly feature 10–25% HVAC duct system leakage, which means homeowners are paying to cool and heat attic spaces and wall cavities instead of the inside of the homes as intended. Aside from the wasted utility costs, leaky ducts create indoor air quality concerns.

Use this guide to help identify, locate, and correct ductwork system leaks.

Signs of Leaky Ducts

You’ll notice some telltale signs if your home’s ductwork is leaky: abnormally warm or cold rooms, high utility bills, dust accumulation around vents, condensation on ducts, and loud whistling or whooshing sounds when the HVAC runs can all indicate leaks. Air leaks allow unconditioned air into the ducts to circulate through the home, contributing to uncomfortable hot or cold spots and higher energy bills.

Pay attention to rooms that are difficult to keep at a comfortable temperature. Faulty ductwork may be to blame if a bedroom, for example, is always hotter or colder than the rest of the house. Ducts to rooms far from the furnace or AC unit are more prone to air leaks.

Drafty rooms, extreme temperature variances between floors, and musty odors are other clues. Leaks near the furnace can even pose a carbon monoxide danger if combustion gases enter your living space.

Locating Leaks

Start your search in your attic, basement, crawlspace, and utility closets where runs of ductwork are exposed. Feel along seams and joints for air movement or condensation. Listen for whistling noises near duct joints. Also check where ducts meet HVAC equipment.

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Pay particular attention to ducts that run through uninsulated spaces like attics and crawlspaces. Even minor gaps here can leak significant conditioned air. Use a flashlight to inspect ducts in hard-to-access areas visually. Damaged sections or detached fittings will be apparent.

Pressure Testing

Before attempting duct repairs yourself, it’s a good idea to thoroughly evaluate your duct system with a professional. A pressure test is one of the best ways they can analyze your ductwork.

First, the technician seals off all the supply and return registers with plastic sheeting. A specific fan is connected to the ductwork to pressurize the system above normal operating pressure. The technician then tracks airflow and leaks using a digital manometer. This test helps locate hidden leaks in sections of ductwork running through walls, floors, and ceilings and allows a contractor to make repairs you couldn’t do on your own.

A pressure test can pinpoint even minor leaks in hidden ducts. Expect to pay around $200 to $400 for the test for a standard-sized home. Tests for larger homes with complex ductwork may cost slightly more.

Typical Problem Areas

Certain parts of duct systems are prone to developing leaks. Here are some of the top areas to inspect closely:

There are potential leak sites where branch lines split off from a main duct run. The rigid metal fittings at branch points can also separate over time.

Elbows, bends, and transitions experience airflow turbulence that can dislodge poorly sealed joints.

The seams where duct sections connect are common leak points. Tape and mastic forming joints can deteriorate over time.

Plenums connect ducts to the central HVAC equipment. Their rigid metal fittings can separate over years of vibration and seasonal temperature changes.

Loose register boots allow conditioned air to escape before entering the room.

DIY Leak Repairs

For small leaks and loose fittings, you can DIY duct repairs using mastic sealant or metal foil tape. Mastic works well for sealing joints and fitting gaps. Apply it over any leaks for a permanent seal.

Metal foil tape also seals well when properly installed. Ensure the duct surface is clean before applying tape. Press the tape firmly in place, smoothing out any bumps or creases. Don’t use regular duct tape, as it degrades and loses adhesion quickly.

Professional Duct Sealing

You’ll want to hire an HVAC professional to repair extensive leaks or sections of damaged ductwork. They have the expertise to seal leaks in your home’s ducts properly and make repairs you can’t easily complete as a DIYer. Expect to pay around $450 to $750 for sealing service in a typical single-family home — cost scales with your home’s size and the number of leaks discovered.

Contractors often spray a mastic sealant inside the ducts’ metal skin at all joints and seams. The compound expands and sets to create an airtight barrier. Remotely accessible ducts may also be re-taped on the outside. Severely damaged air ducts will be replaced by cutting out the affected portion and installing a new duct fitting.

Other HVAC Improvements

Along with sealing duct leaks, here are some other improvements to consider that enhance HVAC efficiency:

  • Air balancing — Adjusting the air flowing to different rooms can help resolve hot or cold spots.
  • Duct cleaning — While not always necessary, cleaning the duct interiors improves air quality by removing dust, pet hair, and other debris.
  • Duct insulation — Uninsulated ducts in unconditioned areas waste energy and require sealing. Insulating ductwork reduces heating and cooling losses.
  • Duct modifications — Altering the duct layout during remodeling or renovations can improve airflow to certain rooms.
  • Equipment maintenance — Keeping equipment like the furnace, AC unit, and air handler maintained improves efficiency. Check filters monthly.
  • Programmable thermostat — Allows you to set different temperatures depending on the time of day and whether you’re home. Not over-cooling or overheating your home when it’s unoccupied saves energy.

Impact on Energy Efficiency

Sealing ducts provides one of the best returns on investment for energy efficiency. Leaky ducts can reduce your system’s efficiency by 20% to 30%. Losing up to 50% of heated and cooled air is not uncommon before it reaches vents. Sealing ducts often cuts your heating and cooling costs by 10% to 20%.

Did You Know

Leaky ducts can reduce your HVAC system efficiency by up to 30%.

The U.S. Department of Energy estimates that the typical home leaks 20% to 30% of its conditioned air through ducts. Fixing these leaks and adding insulation with the proper R-value can save you up to $140 annually. Proper duct sealing keeps conditioned air in the living spaces where you need it. Your system won’t have to work as hard to maintain temperature.

Improving Indoor Air Quality

Beyond saving energy, sealing ducts improves indoor air quality. Leaks allow unconditioned outdoor air, dust, and pollutants to enter the ducts. When you seal the duct system, cleaner interior air recirculates through your home.

Fewer allergens and contaminants entering your ducts mean better air quality. If you hire duct cleaners, sealing leaks beforehand keeps the ducts clean longer. Air leaks can also draw air from moldy crawlspaces or attics into the ducts. Sealing leaky ducts helps prevent this.

HVAC System Efficiency

Efficient ductwork is crucial for adequate airflow and proper HVAC performance. Leaky ducts put more load on your heating and cooling equipment. Your system must work harder to condition air lost through leaks. This accelerated wear can shorten the lifespan of HVAC components.

Sealing ducts allows the system to operate more efficiently because supporting equipment like fans and blowers don’t have to compensate for air loss. Your heating and cooling system will run less often and last longer with fully sealed ducts. Maintaining your HVAC system regularly is also vital for energy efficiency.

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So, Is It Worth Fixing Duct Leaks?

Sealing leaky ducts provides one of the highest returns on investment for homeowners seeking energy savings. The job isn’t prohibitively expensive, especially relative to the resulting long-term savings on energy bills. Few home improvements offer a better payback.

Correcting duct leaks and insulation issues pays for itself in reduced heating and cooling costs within two years, and continues providing savings year after year after that. Sealing duct systems enhances comfort, indoor air quality, and longevity of HVAC equipment. For most homeowners, repairing leaky ductwork is a wise investment.

FAQs About Duct Leaks

How much do duct repairs typically cost?

For minor DIY repairs using mastic and metal tape, you may spend $50 or less. Hiring an HVAC technician to seal ducts professionally averages $450 to $750, depending on your home’s size and the number of leaks. Work on complex systems can cost $1,000 or more.

What are the signs my ducts are leaking?

Clues include certain rooms that are difficult to keep comfortable, high energy bills, dusty vents, condensation on ductwork, dirty spots on insulation, and whistling noises from ducts. Temperature discrepancies between floors or rooms can also indicate leaks.

Do I need to seal brand-new ductwork?

Yes, new ducts often still have minor air leaks at seams and joints. Use mastic sealant on new ducts for an airtight seal. New ducts in unconditioned spaces should also be insulated.

Should I have my ducts regularly cleaned?

No. Consider cleaning ducts if there is a known mold issue or after major remodeling that puts significant dust and debris into the duct system. Cleaning may also improve indoor air quality if you have pets.

Can I use regular duct tape for sealing?

It’s best to avoid standard duct tape for sealing leaks long-term. The adhesive degrades relatively quickly. Use metal foil HVAC tape or mastic instead for a durable seal.

How long does it take to seal ducts?

A professional can usually seal exposed ductwork in a single day. The time varies based on how extensive your leaks are. Any repairs needed to ducts running through walls or hard-to-access areas also add time. In occupied homes, technicians may need to work over two or three days.

Editorial Contributors
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Elisabeth Beauchamp

Senior Staff Writer

Elisabeth Beauchamp is a content producer for Today’s Homeowner’s Lawn and Windows categories. She graduated from the University of North Carolina at Chapel Hill with degrees in Journalism and Linguistics. When Elisabeth isn’t writing about flowers, foliage, and fertilizer, she’s researching landscaping trends and current events in the agricultural space. Elisabeth aims to educate and equip readers with the tools they need to create a home they love.

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Lee Ann Merrill

Chicago-based Lee Ann Merrill has decades of experience writing and editing across a wide range of technical and scientific subjects. Her love of DIY, gardening, and making led her to the realm of creating and honing quality content for homeowners. When she's not working on her craft, you can find her exploring her city by bike and plotting international adventures.

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