You need to properly vent your gas appliances to keep your home safe. As heating technology has advanced, so have methods for venting gasses. In the video above, This Old House plumbing and heating expert Richard Trethewey explains the evolution of venting systems and why it’s important to use certified PVC flue gas ventilation for modern, high-efficiency appliances.
Installing this type of venting system is best left to professionals, but understanding the safety considerations can help you protect your home and know when to call an expert.
The Evolution of Gas Appliance Venting
Gas appliances, such as water heaters, furnaces, and boilers, produce flue gasses that must be safely expelled from your home. These gasses contain several potentially harmful components:
- Carbon monoxide
- Moisture
- Temperature (heat)
Historically, gas appliances were vented using galvanized smoke pipes that connected to a chimney. This system relied on natural drafts to carry the hot flue gasses up and out of the home. However, as appliances became more energy-efficient, venting methods had to adapt to new challenges:
- Lower flue gas temperatures
- Increased moisture content in flue gasses
- Reduced natural drafts
These changes made traditional venting methods less effective and potentially unsafe. High-efficiency systems needed new venting solutions that could handle lower temperatures and higher moisture levels.
Direct Venting and the Rise of PVC
To address the challenges posed by high-efficiency appliances, manufacturers and installers turned to direct venting systems. These systems use fans to push flue gasses out of the home, often through a side wall rather than up a chimney.
The Initial Use of Standard PVC
Many installers created these direct venting systems using standard PVC pipes, commonly used for drain, waste, and vent applications. This choice was driven by several factors:
- Resistance to corrosion from moisture in flue gasses
- Availability at supply stores and home centers
- Easy to work with and install
Despite these advantages, using standard PVC in flue gas venting revealed significant issues over time.
The Problems with Standard PVC for Flue Gas Venting
Standard PVC pipes are not designed to withstand the conditions present in flue gas venting systems. Over time, exposure to heat and temperature fluctuations can cause several issues:
- Brittleness and cracking
- Discoloration of the pipe interior
- Potential for leaks and failure
Trethewey demonstrates how standard PVC pipes can fail when used for flue gas venting, potentially allowing dangerous carbon monoxide to leak into the home.
The Need for Certified PVC Flue Gas Venting
To address the safety concerns associated with standard PVC, experts developed industry standards for safe materials.
UL1738 Standard
The UL1738 standard was established to set requirements for PVC flue gas venting systems. This standard ensures that pipes and fittings used for venting meet certain criteria:
- Designed specifically for flue gas venting
- Clearly marked as approved for gas venting applications
- Tested to withstand the temperatures and conditions present in these systems
Key Requirements of Certified PVC Flue Gas Venting Systems
When using PVC for flue gas venting, it’s essential to adhere to the following requirements:
- Use only pipes and fittings specifically rated for flue gas venting.
- Make sure all components (pipes and fittings) come from the same manufacturer.
- Look for clear markings indicating approval for gas venting applications.
The Importance of Matching Components
The UL1738 standard requires that pipes and fittings come from the same manufacturer. This ensures a proper fit and seal between components, reducing the risk of leaks. Trethewey demonstrates the difference between mismatched and properly matched components in the video above.
Identifying Certified PVC Flue Gas Venting Materials
Here’s what to look for when selecting materials for a flue gas venting system.
Clear Markings
Certified PVC flue gas venting pipes and fittings will be clearly marked with:
- “Gas Vent” or similar wording
- The manufacturer’s name or logo
- UL1738 certification
Consistent Manufacturer
Make sure that all the venting system components, including pipes and fittings, come from the same manufacturer. This helps guarantee a proper fit and seal and reduces the risk of dangerous carbon monoxide leaks.
Proper Sizing
Work with a professional to determine the vent system size for your home. Incorrect sizing can lead to reduced efficiency and potential hazards.
PVC Flue System Installation Considerations
Keep the following tips in mind while your contractor is installing your PVC flue system:
- The system must have proper slope and support for horizontal runs.
- Installers should follow manufacturer instructions precisely.
- Pipes should have enough room to allow for thermal expansion and contraction.
- Installation should be done with appropriate sealants and adhesives designed for flue gas venting applications.
- The system must have adequate clearance from combustible materials.
Don’t be afraid to ask questions throughout the installation.
Maintaining Your PVC Flue Gas Venting System
Regular maintenance helps ensure the continued safe operation of your venting system. Here are some tips:
- Inspect the visible portions of the venting system regularly for signs of damage or discoloration.
- Install and maintain carbon monoxide detectors in your home. Test these detectors monthly.
- Keep vents clear of snow, ice, and debris.
- Have a professional inspect and clean the system annually.
- Replace any damaged components immediately.
Upgrading Existing PVC Flue Systems Systems
If your home has an older venting system that uses standard PVC pipes, we recommend an upgrade. There are several signs that your system may need attention:
- Brittleness or discoloration of the pipes
- Moisture or condensation around the venting system
- Unexplained odors or poor appliance performance
- Visible cracks or damage
If you notice any of these signs, contact a qualified professional to assess your system and recommend appropriate upgrades.
