Stainless Steel Special Gas Venting Systems: Why Do They Often Leak Condensate?

When operating at peak efficiency, high-efficiency boilers produce gallons of acidic condensate per hour, typically at a pH level of 3-5. This condensation is produced inside both the boiler and the exhaust system, but condensate leakage is an all-too-common issue. Anyone who has dealt with a system experiencing leaks understands the damage and costs incurred along with the dreadful task of permanently correcting the problem.

There are three main contributors to a leaking special gas venting system: product design, system design and installation.

Product Design

Special gas venting systems for Category IV appliances must be able to handle continuous static pressure, high-velocity exhaust flow, condensate (which is moving with the exhaust flow and draining back toward the boiler) and temperature cycling.

To ensure maximum efficiency, these boilers must obtain a slight positive pressure at the exhaust outlet. This means that any weak point in the system is subject to leaking, similar to inadequate plumbing. Most product designs for special gas venting utilize an overlapping male/female joint connection to join the sections together. To utilize this joint design, the manufacturer typically incorporates a gasket that enables the system to meet the low-pressure requirement of the UL 1738 listing.

The problem with this setup is that with an overlapping male/female joint connection, the product becomes directional. This forces the exhaust to flow against the overlap due to the condensate that accumulates in the exhaust system, and the condensate must flow back toward the boiler exhaust outlet or back to a drain located in the system.

This exhaust gas, which also contains condensate, can cause issues because it flows directly against the gasket surface. Leakage of the gas and the condensate can easily occur if the product is out of alignment, slightly out of round, or not supported correctly. Since manufacturers of products with this joint design utilize very light gauge material, the product can easily be out of round or have support and alignment issues.

System Design

Proper system design is critical to ensure proper boiler operation and eliminate condensation leakage. For the system to perform adequately, a large amount of condensate must be drained from the exhaust system. The following issues will occur if it is not removed.

• Reduction of the vent ID, which will restrict exhaust flow
• Additional weight added to the system, which may stress joints and system supports
• An increase in acidity as exhaust continues to push into condensate pools, which may cause corrosion of the inner liner

Special gas venting systems’ horizontal runs must be pitched properly to allow the condensate to drain back into the boiler. These runs should also include drains in the system, ideally every ¼” feet (per the NFPA 54/National Fuel Gas Code). Designing the system with the proper amount of pitch is critical to ensure adequate drainage and a leak-free system.

Proper Installation

The efficient operation of UL listed pre-engineered products depends on the installing contractors’ comprehension of the system design documents and the installation instructions provided by the manufacturer. Failure to follow these instructions can hurt product performance and greatly increase the risk of condensate and exhaust gas leaks. Anyone who has been in a mechanical space with a leaking system understands the damage not only accumulated to the venting system but also to anything the condensate comes into contact with.

A special gas vent manufacturer should provide a detailed drawing showing the parts’ locations and details of the supports, hangers, drain sections and roof penetration components. This provides a simple road map for anyone installing the product. If the specific system design is not followed during installation, there is a high probability the system will experience leaks.

Achieving Leak-Free Gas Venting Systems

 Selecting the most robust product, obtaining a complete system design layout, and strict adherence to installation instructions are all key factors in ensuring your special gas venting product is leak-free. Contact us today to get more information and find the best and safest option for you.