7 Most Common Concentric Vent Problems & Solutions!

A concentric vent is a specialized venting system used in appliances like high-efficiency furnaces, water heaters, and boilers. It consists of two separate pipes that are installed together as a single unit.

The inner pipe, known as the exhaust pipe, carries the combustion gases the appliance generates to the outside. The outer pipe, known as the intake pipe, serves as the fresh air supply for the combustion process. It brings in outside air to support efficient and controlled combustion within the appliance.

In this blog, I will tell you about the 7 most common concentric vent problems users face and provide practical solutions.

Whether you’re a homeowner, HVAC professional, or DIY enthusiast, this guide is designed to help you overcome these challenges effectively and ensure the optimal performance of your heating appliances.

7 Most Common Concentric Vent Problems

Concentric vents are often preferred when there are space constraints or when it’s desirable to have a direct venting system.

As sophisticated as they sound, improper maintenance can cause several issues in a concentric vent. Let’s go through them to be safe.

Blockages– Inspect and clean vent pipes
– Use vacuum or brush to remove debris
– Ensure secure connections
Condensation– Insulate vent pipes
– Check slope for drainage
– Install condensate drain or trap
Vent Pipe Separation– Reconnect and secure vent pipe sections
– Seal gaps or leaks
– Verify proper alignment
Incorrect Sizing– Follow manufacturer’s guidelines
– Upgrade or downsize vent pipes as needed
Combustion Air Supply Issues– Inspect and clean air intake
– Install screen/mesh
– Regularly clean air intake
Frozen Concentric Vent– Install insulation
– Use heat tracing cables/tape
– Monitor and provide additional heat sources
Faulty Exhaust Fan– Inspect and clean fan blades
– Check electrical connections
– Repair or replace as necessary


Over time, debris like dust, leaves, or bird nests can accumulate in the vent pipes, obstructing the flow of air and exhaust gases.

This restricts proper ventilation and can lead to decreased appliance performance, inefficient combustion, or potential safety hazards.

Regular inspection and thorough cleaning of the vent pipes are crucial to prevent blockages and maintain optimal venting.


  • Turn off the appliance and allow it to cool completely.
  • Inspect the vent pipes for any visible blockages or debris.
  • Use a vacuum cleaner or a brush to remove any loose debris from the vent pipes.
  • For stubborn blockages, you can use a plumber’s snake or a wire brush to dislodge the debris carefully.
  • Once the blockage is cleared, thoroughly clean the vent pipes using a vent brush or compressed air.
  • After cleaning, ensure that all connections are secure and tightly sealed.
  • Turn on the appliance and check for proper airflow and venting.


Concentric vents, particularly in high-efficiency appliances, are prone to condensation issues.

The temperature difference between the warm exhaust gases and the cooler outside air causes moisture to condense inside the vent pipes.

If not addressed, this moisture can lead to corrosion, water damage, and potential malfunctions in the appliance.

Adequate insulation and proper slope in the vent pipes help mitigate condensation problems by minimizing temperature differentials and facilitating proper drainage.


  • Insulate the vent pipes using appropriate insulation materials designed for venting systems.
  • Check the slope of the vent pipes and ensure they are properly angled for drainage.
  • Install a condensate drain or trap in the vent system to collect and remove any condensation.
  • Regularly inspect and clean the condensate drain or trap to prevent clogs.
  • Consider using a condensate neutralizer if required by local codes or manufacturer recommendations to treat the acidic condensate.

Vent Pipe Separation

Vibrations, thermal expansion, or improper installation can cause the concentric vent pipes to become loose or separate at the joints.

This results in air leakage, disrupting the combustion process and adversely affecting the appliance’s performance.

Regular inspection and maintenance ensure proper alignment, secure connections, and prevent air leakage from impeding the efficiency of the venting system.


  • Carefully examine the vent pipes and joints for any signs of separation or looseness.
  • Securely reconnect any separated or loose vent pipe sections.
  • Use high-temperature silicone sealant or metal foil tape to seal any gaps or leaks at the joints.
  • Verify that the connections are properly aligned and securely fastened.
  • Perform a visual inspection and turn on the appliance to ensure there is no air leakage.

Incorrect Sizing

Concentric vent systems must be appropriately sized according to the appliance’s requirements and the length and configuration of the venting run.

If the vent pipes are undersized or oversized, it can lead to problems such as poor draft, insufficient exhaust flow, or excessive back pressure.

These issues can affect the appliance’s efficiency and cause it to malfunction.

Following the manufacturer’s guidelines and consulting with professionals to determine the correct vent sizing is vital for optimal performance.


  • Refer to the manufacturer’s guidelines or consult an HVAC professional to determine the correct vent pipe sizing for your appliance and venting run.
  • If the vent pipes are undersized, consider upgrading to the appropriate size following local codes and regulations.
  • If the vent pipes are oversized, consult an HVAC professional to assess the potential impact and explore solutions such as installing a reducer or transition piece.
  • Follow proper installation procedures and ensure all connections are secure and airtight.

Combustion Air Supply Issues

The outer pipe in a concentric vent system is responsible for drawing in fresh air for combustion.

If obstructions like snow, leaves, or debris accumulate near the air intake, it restricts the airflow and hampers the appliance’s combustion process.

Regular inspection and timely clearing of any blockages in the air intake are necessary to ensure an adequate combustion air supply and maintain efficient appliance operation.


  • Inspect the air intake for any obstructions such as snow, leaves, or debris.
  • Clear away any blockages and ensure the air intake is free from obstructions.
  • Consider installing a screen or mesh to prevent debris from entering the air intake while allowing proper airflow.
  • Regularly inspect and clean the air intake to maintain an unobstructed combustion air supply.

Frozen Concentric Vent

In colder climates or during freezing weather, condensation inside the concentric vent system can freeze, causing the vent pipes to become blocked.

This hinders the proper venting of exhaust gases and can result in the appliance shutting down or malfunctioning.

Proper insulation, heat tracing, or other measures are necessary to prevent freezing and maintain continuous and unobstructed venting.


  • Install appropriate insulation around the vent pipes to prevent freezing.
  • Consider using heat tracing cables or heat tape specifically designed for vent pipes in cold climates.
  • Ensure that the insulation is installed correctly and covers the entire length of the vent pipes.
  • Monitor the vent pipes during freezing weather and take additional measures, such as adding temporary heat sources near the pipes.

Faulty Exhaust Fan

The exhaust fan within the appliance or the external exhaust fan responsible for removing combustion gases may experience malfunctions or failures.

This can lead to inadequate exhaust airflow, negatively impacting appliance performance and combustion efficiency and potentially posing safety hazards.

Regular maintenance and inspection of the exhaust fan ensure it functions correctly, allowing prompt detection and resolution of any issues.


  • Turn off the appliance and disconnect the power.
  • Inspect the exhaust fan for any visible damage or obstructions.
  • Clean the exhaust fan blades using a soft brush or cloth to remove any dirt or debris.
  • Check the electrical connections and wiring for any loose or damaged components.
  • If the exhaust fan is malfunctioning or damaged, consult an HVAC professional for repairs or replacement.
  • Reconnect the power and test the appliance to ensure the exhaust fan operates correctly.

Concentric Vent Installation – A Diy Guide

Installing a concentric vent system is crucial in ensuring proper ventilation and safety in your construction project. Follow this detailed step-by-step guide to learn how to install a concentric vent easily.

Step 1: Determine Vent Location and Size

  • Use a tape measure to determine the optimal location for the vent based on factors such as clearance requirements, safety regulations, and convenience.
  • Mark the location using a pencil for reference during the installation process.
  • Place a level on the marked location to ensure that the vent will be installed in a straight and level position.
  • This is important for the vent system’s visual aesthetics and functionality.
  • Consult the appliance’s specifications and the manufacturer’s guidelines to determine the correct vent size.
  • Consider factors such as the appliance’s BTU rating, exhaust requirements, and any local building codes or regulations.
  • Choosing the right vent size ensures optimal airflow and efficiency.

Required Tools

  • Tape measure
  • Level
  • Pencil

Step 2: Mark and Cut Openings

  • Mark the locations for the openings on the wall or ceiling where the vent pipes will pass through.
  • Ensure that the marks are level and aligned with the previously determined vent location.
  • To make the cutting process smoother, start by creating a pilot hole at the marked locations using a drill.
  • The pilot hole size should be suitable for your cutting tool and large enough to accommodate the vent pipe.
  • Depending on the wall or ceiling material, choose either a hole saw or a reciprocating saw.
  • Align the cutting tool with the pilot hole and carefully cut along the marked lines.
  • Take your time to ensure clean and accurate cuts.

Required Tools

  • Hole saw or reciprocating saw
  • Drill

Step 3: Install Vent Termination

  • Position the vent termination over the outer vent pipe opening on the exterior wall.
  • Align it properly and use a screwdriver or drill to secure it in place.
  • Depending on the type of vent termination, there may be pre-drilled holes for screw placement.
  • Use screws suitable for the material of the wall and the vent termination.
  • As you fasten the vent termination, securely attach it to the wall.
  • Check for any gaps or loose areas that could compromise the integrity of the connection.
  • To ensure a watertight seal, consider applying an appropriate sealant or gasket around the edges of the vent termination where it meets the wall.
  • This helps prevent water infiltration and potential damage.
  • When installing the vent termination, follow local building codes and regulations to ensure proper clearances from combustible materials.

Required Tools

  • Screwdriver or drill
  • Screws

Step 4: Secure Vent Pipe Assembly

  • Connect the inner and outer vent pipes to the corresponding openings on the vent termination.
  • Ensure a tight and secure fit by aligning the pipes properly and pushing them firmly into place.
  • Some vent pipe assemblies may have locking mechanisms or twist-lock connections that help secure the pipes together.
  • Once the vent pipes are connected to the termination, use a screwdriver or drill to fasten the assembly to the wall.
  • Position the assembly in the desired location and use screws to secure it.
  • The number of screws needed will depend on the size and length of the vent pipe assembly.
  • Place the screws at regular intervals along the assembly to ensure it is held firmly in place.
  • As you secure the vent pipe assembly, ensure it is tightly connected to the termination and wall.
  • Check for any gaps or loose areas that could compromise the effectiveness of the venting system.
  • The connection should be stable and secure to prevent any movement or disconnection that could affect the performance of the venting system.

Required Tools

  • Screwdriver or drill
  • Screws

Step 5: Connect Vent Pipes

  • Select vent pipe connectors that are designed for concentric venting systems and compatible with the size and type of vent pipes being used.
  • These connectors ensure a proper and secure connection between the inner and outer vent pipes.
  • Slide the inner vent pipe into the outer vent pipe, ensuring they fit together snugly.
  • Align the openings of the pipes to ensure a clear and unobstructed passage for the exhaust gases.
  • Depending on the vent pipe connectors being used, you may need to insert them into the ends of the pipes before joining them together.
  • Once the inner and outer vent pipes are properly aligned, use screws or clamps to secure the connections.
  • If your vent pipe connectors have screw holes, insert screws through the holes and tighten them to hold the pipes in place.
  • Alternatively, use clamps designed for vent pipes to secure the connections tightly.
  • Ensure that the screws or clamps are tightened adequately, but be careful not to overtighten and damage the pipes or connectors.
  • After securing the connections, visually inspect them to ensure they are properly aligned and there are no gaps or loose areas.
  • The connections should be airtight and secure to maintain the integrity of the venting system.

Required Tools

  • Vent pipe connectors
  • Screws or clamps

Step 6: Secure Vent Pipe to Structure

  • Identify the areas on the structure where you can securely fasten the vent pipe assembly.
  • These attachment points should be structurally sound and capable of supporting the weight of the vent pipe.
  • Use brackets or straps designed for vent pipe installations.
  • Position the brackets or straps around the vent pipe assembly, ensuring they are properly aligned with the attachment points on the structure.
  • Ensure the brackets or straps are wide enough to securely hold the vent pipe assembly in place.
  • Use a screwdriver or drill to fasten the brackets or straps to the structure.
  • Insert screws through the pre-drilled holes in the brackets or straps and tighten them securely.
  • Ensure that the brackets or straps are tightly secured to provide adequate support and prevent any movement or vibration of the vent pipe assembly.
  • Once the brackets or straps are securely attached, check the stability and support of the vent pipe assembly.
  • Shake the assembly gently to ensure it is firmly in place and does not wobble or shift.
  • The vent pipe should be stable and securely fixed to the structure.

Required Tools

  • Screwdriver or drill
  • Brackets or straps

Step 7: Install Vent Collar and Seal Connections

  • Place the vent collar around the openings of the inner and outer vent pipes.
  • Ensure that the collar fits snugly and aligns with the vent termination on the exterior wall.
  • Position the collar so that it provides a finished and aesthetically pleasing appearance.
  • Use screws or clamps to secure the vent collar in place.
  • Depending on the design of the collar, you may need to insert screws through pre-drilled holes or tighten clamps around the collar.
  • Ensure that the collar is securely fastened and does not move or shift.
  • Apply silicone sealant to the connections between the vent pipes, vent collar, and vent termination.
  • Use a silicone sealant designed for high-temperature applications and suitable for use with venting systems.
  • Apply a continuous bead of sealant around the connections to create an airtight seal and prevent any air leaks.
  • Use a sealant smoothing tool or a gloved finger to smooth and flatten the silicone sealant.
  • This helps ensure a neat, uniform seal and better adhesion to the vent pipes and collar.
  • It usually takes several hours or even a full day for the sealant to cure fully.
  • Avoid disturbing or manipulating the connections until the sealant has cured completely.

Required Tools

  • Screwdriver or drill
  • Screws or clamps
  • Silicone sealant

Step 8: Insulate Vent Pipe

  • Choose an insulation material that is specifically designed for use with vent pipes.
  • Insulation sleeves or wraps made of materials such as fiberglass or foam are commonly used for this purpose.
  • Ensure that the insulation material is compatible with the diameter and type of vent pipe being used.
  • Measure the length of the vent pipe that needs to be insulated.
  • Cut the insulation material to the appropriate length, allowing some overlap for a secure fit.
  • Wrap the insulation material tightly around the vent pipe, ensuring that it covers the entire length that needs to be insulated.
  • The insulation should fit snugly without any gaps or loose areas.
  • Use insulation tape or clamps to secure the insulation in place.
  • If using insulation tape, wrap it around the insulation at regular intervals to hold it firmly in position.
  • Alternatively, if using clamps, place them around the insulation and tighten them.
  • Inspect the insulation for any gaps or joints where heat could escape.
  • Use insulation tape or sealant to seal these areas and ensure a tight seal.
  • If multiple sections of the vent pipe need insulation, repeat the above steps for each section.

Required Tools

  • Insulation material
  • Insulation tape or clamps

Step 9: Test Vent System

  • Connect the HVAC system to the vent system using the appropriate connections.
  • Ensure that all connections are securely fastened and properly aligned.
  • Depending on the specific requirements of the HVAC system and venting setup, prepare the necessary tools for system testing.
  • This may include a manometer to measure pressure differentials and a smoke pencil to detect air leaks.
  • Start the HVAC system and allow it to operate for a sufficient amount of time to reach normal operating conditions.
  • This ensures that the vent system is under typical operating conditions during testing.
  • Carefully observe the airflow from the vent system.
  • Ensure a steady and consistent flow of air from the inner and outer vent pipes.
  • Check for any signs of blockages or obstructions in the venting system.
  • If any issues or abnormalities are observed during testing, take note of them and investigate further.
  • This may include air leaks, inadequate airflow, or other problems that could affect the performance of the vent system.
  • Address any identified issues promptly, following the manufacturer’s instructions or consulting with an HVAC professional if necessary.

Required Tools

  • HVAC system
  • Manometer
  • Smoke pencil

Step 10: Complete Finishing Touches

  • Using a screwdriver or drill, secure the vent system in place by attaching screws or trim pieces as needed.
  • This helps to provide stability and prevent any movement or displacement of the vent pipes and components.
  • Carefully inspect all connections within the vent system, including the joints, connectors, and collars.
  • Ensure they are correctly sealed and tightened to prevent any air leaks.
  • If any connections appear loose or require adjustment, use the appropriate tools to make the necessary modifications.
  • Pay attention to the vent pipes’ alignment, the termination placement on the exterior wall, and the overall neatness of the installation.
  • This may include realigning the vent pipes, securing loose connections, or making aesthetic improvements to enhance the overall appearance of the installation.

Required Tools

  • Screwdriver or drill
  • Screws or trim pieces

Final Verdict

In conclusion, understanding and addressing the most common concentric vent problems is essential for maintaining your HVAC appliances’ optimal performance, efficiency, and safety.

Maintaining a clean combustion air supply by regularly inspecting and clearing any obstructions is important for optimal appliance performance.

Taking precautions against freezing, such as proper insulation and heat tracing, prevents vent blockages and malfunctions during cold weather.

Regular maintenance and inspection of the exhaust fan ensure proper exhaust airflow and safe operation.

Remember, proactive maintenance and prompt problem-solving are key to ensuring optimal functionality and peace of mind when it comes to your home’s ventilation system.


Does a concentric vent need a rain cap?

Yes, a concentric vent typically requires a rain cap for protection. Unlike standard vent terminations, the design of a concentric vent includes a small pipe extending out from a cone or saucer. This pipe is susceptible to the entry of birds and insects. To prevent this, it is important to install a suitable cap with a screen to protect the opening and ensure proper ventilation while keeping unwanted debris and creatures out.

How high does a concentric vent need to be?

The height of a concentric vent must meet specific requirements for proper installation. It should terminate vertically and be positioned at a minimum height of 12 inches (30.5 cm) above the highest expected snow level (18 inches or 45.7 cm for Canada). The vent should not exceed a maximum height of 24 inches (61 cm) above the roof.

How long can concentric vent be?

A concentric vent can be extended up to 60 inches by replacing the piping between the concentric Y fitting and the rain cap. This allows for flexibility in the installation, accommodating different distances between the appliance and the vent termination point.