Can You Use Existing Vent for Tankless Water Heater: Get It Here!

Debarghya Roy

Vent For Tankless Water Heater

As home upgrades trend towards energy efficiency, many homeowners are exploring the benefits of tankless water heaters. However, a common challenge they face is whether their existing vents are compatible with this new technology.

This article seeks to demystify venting requirements for tankless water heaters and offer guidance on evaluating the suitability of your current system. Read on to find why choosing the right vent for your tankless heater matters as much as selecting the device itself.

Vent of tankless water heater

Key Takeaways

  • Existing vents such as galvanized pipes may not be compatible with tankless water heaters due to rusting issues, necessitating the use of stainless-steel vents or other suitable materials.
  • Tankless water heaters offer three main types of venting options: power vent, direct vent, and concentric vent. Each has specific requirements and considerations for compatibility with existing vents.
  • Proper ventilation is essential for safe operation and optimal performance of tankless water heaters. Using improper vents can lead to issues like carbon monoxide leaks, inefficient combustion, or inadequate ventilation.
  • It is important to consult manufacturer guidelines and seek professional assistance when evaluating the compatibility of existing vents with tankless water heaters. Specific requirements for vent size, material selection, clearances, and termination points should be followed for a reliable installation.

Types of Venting for Tankless Water Heaters

There are three main types of venting for tankless water heaters: power vent, direct vent, and concentric vent.

Power Vent

A power vent is a key component of your tankless water heater system, particularly designed to safely discharge the combustion gases produced during operation. This type of vent employs an electrically-powered fan or blower for pushing the exhaust gases out.

Unlike traditional water heaters that may rely on natural air convection, a power vent offers consistent and efficient ventilation regardless of external conditions. Moreover, it extends compatibility by allowing you to place your tankless water heater in more varied locations within your home due to its active expulsion design.

However, one must note that the existing vents such as galvanized ones may not be compatible with most applications because they can rust quickly necessitating stainless-steel vents as per non-condensing tankless gas heaters requirement.

The proper installation and maintenance are paramount for safety and effectiveness of a power-vented system.

Direct Vent

A direct vent is a popular venting option for tankless water heaters. It involves using a sealed pipe system that draws in air from outside and exhausts combustion gases directly outside as well.

This eliminates the need for complex ductwork or chimneys.

One important aspect of direct venting is that it ensures indoor air quality by preventing any combustion byproducts from entering your living space. Additionally, it allows for flexibility in installation since the intake and exhaust pipes can be directed through an exterior wall instead of relying on existing vents.

Direct venting also offers energy efficiency benefits. Because it brings in fresh outdoor air, there is no risk of negative pressure inside your home, which could potentially hinder proper combustion or cause back drafting.

When considering direct vent compatibility with your existing vents, keep in mind that this type of venting requires specific materials and installation guidelines to ensure safety and optimal performance.

It’s crucial to follow manufacturer recommendations and consult a professional if you’re unsure about compatibility or need assistance with retrofitting existing vents for your tankless water heater installation.

Concentric Vent

A concentric vent is a type of venting system commonly used for tankless water heaters. It consists of two pipes, one within the other, allowing both combustion air intake and exhaust to pass through a single opening.

This innovative design not only simplifies the installation process but also ensures efficient operation by keeping the intake and exhaust gases separate. With a concentric vent, you can save space while maintaining safety and meeting ventilation requirements for your tankless water heater.

It’s important to note that not all tankless water heaters are compatible with this type of venting system, so it’s crucial to check manufacturer guidelines to determine if your unit supports concentric vents.

Compatibility of Existing Vents with Tankless Water Heaters

Using existing vents for tankless water heaters can be problematic due to the potential rusting of galvanized vent piping and the specific venting requirements of tankless water heaters.

Importance of proper venting

Proper venting is essential when it comes to installing a tankless water heater in your home. Using the correct venting system ensures that harmful gases, such as carbon monoxide, are safely expelled from your living space.

It also helps maintain optimal performance and efficiency of the water heater. When existing vents are not compatible with tankless water heaters, issues like rusting of galvanized pipes can occur, potentially leading to leaks or blockages in the ventilation system.

By understanding the importance of proper venting and following the specific requirements for tankless water heaters, you can ensure not only safe operation but also peace of mind knowing that your family’s health and well-being are protected.

Potential issues with using existing vents

Using existing vents for a tankless water heater may lead to several potential issues. It’s important to consider these factors before deciding to use your current venting system:

  1. Rusting: Existing vent pipes are typically galvanized, which can rust quickly when exposed to the high moisture content of combustion gases from a tankless water heater.
  2. Size and Material Compatibility: Existing vents may not meet the size and material requirements specified by the manufacturer for proper installation of a tankless water heater. Different models have specific requirements that must be followed for safe operation.
  3. Venting Restrictions: Tankless water heaters may have specific restrictions on common venting methods, such as sharing a vent with other appliances or using masonry chimney flues. It’s essential to understand these restrictions and ensure compliance.
  4. DIY Installation Challenges: If you’re installing the tankless water heater yourself, using existing vents can present challenges in terms of proper alignment, sealing, and overall compatibility with the new unit.
  5. Exhaust Venting Considerations: The exhaust venting requirements for tankless water heaters may differ from traditional tank-style units. The size and type of vent pipe needed will depend on whether you have a noncondensing or condensing tankless water heater, which requires different ventilation systems.
  6. Outdoor Installation Constraints: If you plan on installing your tankless water heater outdoors, using existing vents might not be practical or even possible due to location limitations or lack of suitable connections.
  7. Safety Concerns: Vent compatibility is crucial for safe operation of a tankless water heater. Using improper vents can result in carbon monoxide leaks or inadequate ventilation, posing serious health risks for occupants.

Vent with rust on it

Venting Requirements for Tankless Water Heaters

Tankless water heaters have specific venting requirements, including size and material specifications, as well as proper installation guidelines.

Size and material requirements

Proper vent sizing and material selection are crucial for the safe and efficient operation of a tankless water heater. Here are some important size and material requirements to consider:

  1. Vent Size: The size of the venting system should be suitable for the specific tankless water heater model being installed. Refer to the manufacturer’s guidelines or consult a professional to determine the appropriate vent size.
  2. Material: Different types of tankless water heaters may require different vent materials. For noncondensing tankless gas heaters, stainless-steel vents are recommended as they can withstand high exhaust temperatures without corroding. On the other hand, condensing tankless water heaters with cooler exhaust can use PVC or CPVC vents, which are more cost-effective.
  3. Vent Length: The length of the venting system plays a role in determining its efficiency. Shorter, straighter vent runs generally provide better performance compared to longer, more complex ones. It is important to follow the manufacturer’s guidelines regarding maximum vent length and any necessary offsets or elbows.
  4. Vent Termination: The location where the vent exhausts outside is also important. A proper termination point ensures that exhaust gases are safely expelled without creating a hazard or causing damage to nearby structures or equipment. Common termination options include through-the-wall vent caps and roof-mounted caps.
  5. Clearances: Make sure to maintain proper clearances between the venting system and combustible materials such as wood framing or insulation. These clearances help prevent heat transfer that could potentially start a fire.
  6. Professional Installation: It is highly recommended to have a professional HVAC technician install or inspect your tankless water heater’s ventilation system to ensure compliance with local codes and safety standards.

Proper installation guidelines

To ensure the proper installation of a tankless water heater venting system, follow these guidelines:

  1. Consult the manufacturer’s instructions: Each tankless water heater model may have specific venting requirements outlined in the manufacturer’s instructions. It’s important to review and follow these guidelines for optimal performance and safety.
  2. Hire a professional installer: While some handy homeowners may attempt a DIY installation, it is highly recommended to hire a professional installer experienced in working with tankless water heaters. They will have the knowledge and expertise to ensure proper vent sizing, material selection, and installation procedures.
  3. Consider local codes and regulations: Venting codes and regulations may vary by location, so it’s crucial to familiarize yourself with any specific requirements in your area. These codes often dictate factors such as vent size, termination distance from windows or doors, clearance from combustible materials, and more.
  4. Choose the right vent type: Depending on your tankless water heater model and application, you’ll need to select the appropriate vent type (power vent, direct vent, or concentric vent). This decision is influenced by factors such as space availability, combustion air source options, and local code requirements.
  5. Size the vent correctly: Proper vent sizing is essential for efficient operation of your tankless water heater. The manufacturer’s instructions will provide guidelines for determining the appropriate diameter of the vent pipe based on factors such as BTU output and total length of run.
  6. Use approved materials: When selecting materials for your tankless water heater venting system, refer to the manufacturer’s instructions for approved options. Noncondensing gas tankless water heaters often utilize stainless-steel vents that can withstand high exhaust heat without corroding or deteriorating.
  7. Ensure proper slope and support: The vent pipe should be installed with the correct slope to allow condensation or moisture to drain back into the unit effectively. Additionally, proper support should be provided at regular intervals to prevent sagging or shifting of the vent pipe.
  8. Consider termination location: The termination point of the vent pipe, where exhaust gases are released outdoors, should be carefully chosen. It should comply with local code requirements and be positioned away from windows, doors, and areas where exhaust fumes can accumulate.
  9. Test for proper operation: After installation, it’s crucial to test the tankless water heater’s venting system for proper operation. Check for any signs of back drafting, such as unusual odors or soot accumulation around the unit.

Frequently Asked Questions

1. Can I use my existing vent system with a tankless water heater?

The compatibility of your existing vent system with a tankless water heater depends on factors such as the type of vent, size and configuration. It is recommended to consult a professional plumber or HVAC technician to assess the compatibility and make any necessary modifications.

2. What are the common types of vents used with tankless water heaters?

Common types of vents used with tankless water heaters include direct venting, power venting, and concentric venting. Each type has specific requirements and installation guidelines that should be followed for optimal performance and safety.

3. How do I know if my existing chimney can be used with a tankless water heater?

It is important to have your chimney inspected by a professional to determine its suitability for use with a tankless water heater. Factors such as size, condition, clearance requirements, and local building codes will influence whether it can be utilized or if alternative venting options need to be considered.

4. Do I need to install additional ventilation for my tankless water heater?

Depending on the specific model and installation location, additional ventilation may be required to ensure proper air circulation and exhaust removal for the tankless water heater. A qualified technician will assess the needs during installation and recommend any necessary modifications or additions for safe operation.


In conclusion, understanding the compatibility of existing vents with tankless water heaters is crucial for a safe and efficient installation. Using galvanized vent piping may not be suitable due to rusting issues, and proper ventilation requirements must be met for optimal performance.

It is important to consult specific guidelines from manufacturers like Rinnai and consider any necessary modifications or upgrades to ensure the successful venting of your tankless water heater.

By following these considerations, you can enjoy the benefits of a tankless water heater while maintaining a reliable ventilation system.

About the author

Debarghya Roy: A heating systems author, Passionate about energy efficiency and sustainability, Sharing insights and empowering readers through informative blog articles.