Gas piping installation

What is going on

Gas piping to the furnace is simple once you know the rules. Upflow units ship set up for left-side gas piping, and there is a right-side knockout if the gas comes in from the other side. What matters is sizing the pipe for the load, putting in a shutoff and union so the furnace can be serviced, and a drip leg to catch dirt and moisture before it reaches the gas valve. Always leak-test with soap solution, never a flame.

Likely causes

• Undersized pipe starving the furnace at full fire
• No drip leg letting debris reach the gas valve
• Gas valve damaged by wrenching without a backup
• Wrong pipe compound on propane
• Leaking joints from poor assembly

Check in this order

1. Size piping using the pipe capacity table for the required cfh and run length.
2. Install a ground joint union and a manual shut-off valve ahead of the furnace.
3. Install a condensation drip leg ahead of the controls as required by national codes.
4. Use a backup wrench on the gas valve when connecting piping to prevent damage.
5. Use pipe joint compound that resists liquefied petroleum gases.
6. Check all gas joints for leaks with soap solution. Never use an open flame.
7. Have a licensed gas fitter do the work and do a final leak check with the furnace firing.

More furnace guides

• Abnormal conditions and protection
• Adjust gas valve manifold pressure
• Air for combustion and ventilation in non-direct vent installs
• Airflow adjustment check
• Airflow and temperature rise check
• Bottom return filter rack installation (upflow)