A drip leg, also known as a “drip,” is a crucial component in a gas furnace system, designed to collect condensation and other contaminants that can potentially cause issues with the gas flow and the furnace’s operation. This comprehensive guide will explore the purpose, function, code requirements, ideal installation, and potential costs associated with a gas furnace drip leg.
What is the Purpose of a Drip Leg in a Gas Furnace?
The primary purpose of a drip leg in a gas furnace is to collect condensation and other contaminants that may be present in the gas line. This is particularly important in systems where the gas is considered “wet,” meaning it has a moisture content that can condense within the piping.
How Does a Drip Leg Function in a Gas Furnace?
A drip leg serves two main functions:
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Condensation Collection: The drip leg is designed to capture any condensation that forms in the gas line, preventing it from entering the gas valve or burner of the furnace. This helps maintain the integrity of the gas flow and prevents potential malfunctions or safety hazards.
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Debris Collection: While primarily intended for condensation, drip legs can also collect other debris such as sediment, rust, or dust that might be present in the gas line.
What are the Code Requirements for a Drip Leg in a Gas Furnace?
The installation of a drip leg in a gas furnace is typically required by code, especially in situations where the gas is considered “wet.” The specific code requirements are outlined in the International Fuel Gas Code (IFGC) and local codes based on it.
Where Should a Drip Leg Be Installed in a Gas Furnace?
The ideal location for a drip leg in a gas furnace system is at the lowest points in the gas piping, ensuring that condensation and debris collect there rather than flowing back into the gas meter or entering the appliance. The drip leg should be installed upstream of the gas valve, typically after the shutoff valve and before the flexible gas connector.
How to Install a Drip Leg in a Gas Furnace?
The installation of a drip leg in a gas furnace typically involves the following steps:
- Gather the necessary materials, including a black iron tee fitting, black iron nipples (4-6 inches long), and a black iron cap.
- Install the tee fitting at the desired location, usually at a low point in the piping or just before the appliance.
- Attach a short nipple (4-6 inches) to the bottom of the tee and cap the end.
- Connect the gas line to the side of the tee, ensuring that the gas flow is directed towards the appliance.
What are the Measurements and Tools Needed for a Drip Leg in a Gas Furnace?
The depth of the drip leg (nipple) should be at least 3 inches or equal to the internal diameter of the piping, whichever is greater. The diameter of the drip leg should be the same as or less than the diameter of the piping it serves.
The tools required for the installation of a drip leg include a pipe wrench or adjustable wrench, Teflon tape or pipe dope, a pipe cutter (if necessary), and the necessary threaded fittings and caps.
What are the Potential Costs of a Drip Leg in a Gas Furnace?
The cost of materials for a drip leg, including the tee fitting, nipples, and cap, typically ranges from $10 to $50, depending on the specific components and their quality. If hiring a professional for the installation, the labor cost will depend on the location and the technician’s rates. However, if installed during the initial setup of the furnace, the cost is often included in the overall installation price.
Reference:
1. Drip legs for Tankless W/H – Home Inspection
2. HVAC – Drip leg vs. Sediment trap – InterNACHI®️ Forum
3. drip leg on gas line for new furnace – HVAC-Talk
