Gas supply piping layout

What is going on

Gas piping has to be sized so the valve gets enough pressure when everything is running, and set up so the valve can be serviced later. Think about the next tech when you build it. A union near the cabinet, a shutoff you can reach and a drip leg all make life easier and keep dirt out of the valve. Everything must follow local codes and the utility's rules, and gas piping is licensed work in most places, so have a qualified gas fitter do it.

Likely causes

• New furnace install needing a gas line run
• Undersized line that causes low pressure under load
• No place to remove the gas valve for service
• Dirt or scale in the line fouling the valve
• Shared line with other appliances that drops pressure

Check in this order

1. Run a separate gas line from the meter to the furnace where possible
2. Size the gas line and manual gas stop so pressure drop is not excessive, and never smaller than the pipe size to the gas valve
3. Use Table 12 for natural gas or Table 13 for LP to select pipe size
4. Install a ground joint union within 3 ft of the cabinet so the gas valve can be removed
5. Install a manual shut-off valve outside the furnace casing and upstream of the union, within easy reach
6. Install a drip leg in the supply line as close to the furnace as possible
7. Leak-test all joints with an approved method before putting the furnace in service

More furnace guides

• Annual and start-of-season inspection
• Blower codes 66, 61 and 60 - what to look for
• Blower does not start after burners light
• Burners go out before the heat call ends / short cycling
• Canada only: derate high altitude by lowering manifold pressure
• Cement PVC vent joints