Where does the gas shutoff valve have to be for a furnace, and do I need a drip leg?

Furnace Gas Shutoff Valve Location

The gas shutoff valve must be installed within 6 feet of the furnace and readily accessible without tools (IRC Section G2418.2). It should be on the upstream (supply) side of the furnace, before the gas enters the unit. The valve must be a manual, full-port ball valve or similar approved type.

Drip Leg Requirement

Yes, a drip leg (sediment trap) is required by IRC Section G2419.12. It must be installed on the appliance side of the shutoff valve, before the gas connection to the furnace. The drip leg should:

• Be a minimum 3-inch vertical pipe drop
• Use a tee fitting oriented so the outlet faces downward
• Include a capped nipple to collect debris and condensate

Installation Notes

• Use proper gas-rated piping (black iron, CSST, or approved flexible connectors)
• Ensure all joints are properly sealed with gas-rated thread sealant or tape
• Test for leaks with a soap solution or electronic leak detector after installation
• Some local codes may have additional requirements—check with your AHJ

Safety Warning: Gas work can be dangerous. If you're not experienced with gas piping, hire a licensed HVAC technician or plumber. Improper installation can cause leaks, fire, or carbon monoxide poisoning.

Location (IRC G2420.5 / IFGC 409.5): The shutoff valve must be in the same room as the furnace, upstream of the union/connector, and readily accessible (no tools/ladders required). It must be within 6 feet of the appliance and installed upstream of the sediment trap (drip leg) so the trap can be cleaned without shutting off gas to the whole house.

Drip Leg (Sediment Trap) – Required (IRC G2419.4 / IFGC 408.4): Yes. A sediment trap is mandatory immediately upstream of the furnace gas valve (before the flexible connector if used).

• Construction: Tee fitting with a capped nipple ≥ 3 inches long (vertical drop) on the bottom outlet. Gas flows horizontally through the run of the tee; debris falls into the leg.
• Orientation: Must be vertical (or within 45° of vertical) to collect debris.
• Exception: Not required if the furnace has an integral trap listed for that purpose (rare on residential units).

Pro Tip: Install: Shutoff Valve → Union → Drip Leg → Flex Connector → Furnace Gas Valve. This order lets you drop the trap for cleaning without breaking the gas line upstream.

Code Check: Verify local amendments; some jurisdictions require the valve outside the furnace closet (on the exterior wall) for servicing without entering the space.