Condensing Furnace Drain Guidance w/ AC Service Tech

HVAC School - For Techs, By Techs

Bryan and Craig Migliaccio (AC Service Tech)dive deep into the complexities of managing condensate drainage in high-efficiency (90%+) gas furnaces. The conversation begins with a clear explanation of why these furnaces produce condensate in the first place - they have two heat exchangers that extract so much heat from the combustion gases that water vapor condenses out. This condensate is acidic (pH 3-5) and requires special consideration for drainage and disposal.

The discussion explores various challenges contractors face when installing these systems, particularly in cold climates where freezing is a concern. Craig shares practical solutions from his experience in New Jersey, including using larger diameter pipes for exterior drainage and creating air gaps to prevent complete freezing. They address the ongoing debate about whether to combine AC condensate lines with furnace condensate lines, noting that while it's technically possible, there are potential risks and code considerations to keep in mind.

A significant portion of the conversation focuses on code compliance and best practices for condensate disposal. The International Mechanical Code (IMC) provides several acceptable options for drainage, including floor drains, utility sinks, and standpipes. However, as Craig points out, local interpretations and requirements can vary significantly, making it crucial for contractors to maintain good relationships with their local inspectors and understand their specific jurisdiction's requirements.

Key Topics Covered:

• How 90% efficient furnaces produce condensate through their dual heat exchanger system
• The acidic nature of furnace condensate and its corrosion potential
• Solutions for preventing condensate line freezing in cold climates
• Pros and cons of combining AC and furnace condensate lines
• Code-compliant drainage options (IMC 307.2)
• Use of condensate pumps as a solution for difficult drainage situations
• Importance of proper trapping and venting in condensate systems
• Requirements for auxiliary drain pans under furnaces
• Role of condensate switches and safety controls
• Challenges with different installation locations (crawl spaces, basements, etc.)
• Considerations for neutralizer usage when draining into septic systems
• Best practices for maintaining professional relationships with code officials

Check out some of Craig's great educational books at https://www.acservicetech.com/.

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