How To Fix Leaks in Air Ducts

Leaky air ducts significantly impact your home’s energy efficiency, increasing utility bills and reducing comfort. In this article, This Old House host Kevin O’Connor and energy auditor Paul Scheckel demonstrate how to identify and repair leaks in air ducts, potentially saving homeowners up to 20% on heating and cooling costs.

Air Duct Leakage

Air duct leakage is a common problem in many homes, especially those built before the 1990s. Leaks can occur at joints, seams, and connections in the ductwork, allowing conditioned air to escape into unconditioned spaces like attics or crawl spaces.

Causes of Duct Leakage

Several factors can contribute to air duct leakage, including:

• Poor installation or inadequate sealing during initial construction may leave gaps and weak spots
• Aging and deterioration of duct materials over time, resulting in breaks and tears
• Damage from pests or accidental impacts causing physical breaches
• Improper maintenance or modifications to the HVAC system leading to unintended leaks

Impact on Energy Efficiency

Leaky ducts can significantly impact your home’s energy efficiency and comfort by causing:

• Increased energy consumption and higher utility bills
• Uneven heating and cooling throughout the house
• Reduced indoor air quality due to dust and pollutants entering the system
• Increased wear and tear on HVAC equipment

Identifying Air Duct Leaks

Before you can fix leaks in your air ducts, you need to locate them. Kevin and Paul showcase effective methods for identifying duct leaks and offer homeowners practical solutions to manage this issue.

Using a Duct Blaster

A duct blaster—which, most of the time, can be rented from an equipment rental service—is a specialized fan that pressurizes the duct system to help locate leaks. Here’s how to use it effectively:

1. Seal all supply and return registers in the house with tape.
2. Attach a duct blaster fan to a section of flexible duct, then attach the opposite end of flexible duct to the existing heating duct.
3. Use a pressure-and-flow gauge to measure air pressure in the ducts.
4. Aim for a pressure reading of about 25 pascals.

If the pressure reading is significantly lower than 25 pascals, it indicates substantial leakage in the duct system. 

Smoke Testing

After pressurizing the system with a duct blaster, you can use smoke to identify leak locations visually. This method is simple yet effective:

1. Introduce smoke into the ductwork using a theatrical fog machine.
2. Observe where smoke escapes from the ducts.
3. After the fog clears, use a smoke pencil to check specific joints and seams for leaks.

Any smoke escaping from the ductwork represents a leak and potential energy loss.

Steps To Seal Air Duct Leaks

Here are the steps to effectively seal your air ducts:

Step 1: Remove Old Tape

1. Locate any cloth-backed utility tape on the ductwork.
2. Carefully peel off the old tape, which is likely to fail over time.
3. Clean the surface of any residue to prepare for proper adhesion of new sealants.

Removing old tape provides a clean surface, which will provide a long-lasting seal.

Step 2: Apply Duct Sealant

1. Put on disposable gloves to protect your hands.
2. Use a high-quality duct sealant or Mastic.
3. Apply the sealant generously to all joints, seams, and connections.

A healthy application of duct sealant prevents future leaks.

Step 3: Seal With Foil-Faced Duct Tape

1. Cut appropriate lengths of foil-faced duct tape. Do not use regular, cloth-backed duct tape.
2. Apply the tape over sealed joints for added protection.
3. Smooth out any bubbles or wrinkles for a tight seal.

Using foil-faced duct tape adds an extra layer of protection, reinforcing the seal made by the duct sealant.

Insulating Air Ducts

After sealing the leaks, insulating the ductwork is important to prevent energy loss through conduction. Paul recommends using R-6 foil-faced fiberglass insulation for optimal results. 

Choosing the Right Insulation

When selecting insulation for your air ducts, consider the following factors to ensure optimal efficiency and safety:

• R-value: The R-value measures the insulation’s resistance to heat flow. A higher R-value means better insulation, which helps maintain the desired temperature in your ducts, reducing energy loss and lowering heating and cooling costs.
• Vapor barrier: Insulation with a vapor barrier prevents moisture from condensing on the duct surfaces, which can lead to mold growth and corrosion over time. Ensure the insulation has a reliable vapor barrier to protect your ductwork and maintain indoor air quality.
• Fire resistance: Insulation materials should have a fire-resistance rating that meets local building codes and safety standards. Choosing insulation with a high fire resistance rating can help prevent the spread of fire through the ductwork in the event of an emergency.
• Ease of installation: Consider insulation that is easy to handle and install, especially if you’re doing a DIY project. Flexible materials that fit snugly around ducts without gaps ensure effective insulation and reduce the risk of air leaks.

Insulation Installation Process

Confirm full coverage and secure the insulation tightly around the ducts to maximize efficiency:

1. Measure and cut the insulation to fit snugly around the ductwork.
2. Wrap the insulation around the ducts and provide full coverage.
3. Secure the insulation with foil-faced duct tape.
4. Pay special attention to joints and seams to prevent gaps.

Benefits of Proper Air Duct Sealing and Insulation

There are numerous benefits to insulating your ducts, including the following:

• Reduced energy consumption and lower utility bills
• Improved indoor air quality by preventing dust and pollutants from entering the system
• More consistent temperatures throughout your home
• Extended lifespan of your HVAC equipment due to reduced strain

When To Call a Professional

While many homeowners can tackle basic duct sealing and insulation, some situations may require professional assistance. Recognizing when to call a professional can save time and ensure thorough repairs:

• Ducts located in hard-to-reach areas like crawl spaces or attics might require specialized equipment
• Extensive damage or deterioration of the ductwork may be beyond do-it-yourself efforts
• Concerns about asbestos or other hazardous materials require expert handling
• Lack of proper tools or equipment for thorough testing and sealing points to the need for a professional

Professionals have the expertise to manage complex situations and can offer peace of mind with their experience and guarantee of the work they complete.