Adding Range and Fireplace Load to an Undersized Gas Main
A 1950s house has 3/4-inch Schedule 40 black iron gas piping from the meter with a developed length of 40 feet to a tee that feeds an 80,000 BTU/hr furnace and a 40,000 BTU/hr storage water heater. Supply pressure at the meter regulator is standard low pressure, 7 inches water column, and the existing table values for 3/4-inch at 40 feet give roughly 130,000 BTU/hr. The owner is adding a 65,000 BTU/hr range in the kitchen, 15 feet of new run off that same tee (25 feet developed length to the range), and wants to reuse a flexible connector he already owns. The inspector has asked for gas sizing and a pressure test before the meter is turned on.
1. Size the new work. Show the load calculation and explain why the existing 3/4-inch main cannot simply be tapped.
Read the worked answer
Connected load at the tee: 80,000 furnace + 40,000 water heater + 65,000 range = 185,000 BTU/hr. Adding the fireplace or any future appliance must be added here too, not later.
Longest-length method: the governing length is the longest developed run from the meter to the farthest appliance, including an allowance for fittings. If the range run is 25 feet developed and the existing main is 40 feet, the governing length is the longer of the two paths - 40 feet to the furnace/water heater, 25 feet + 40 feet? No: the range path is 40 feet to the tee plus 15 feet to the range, so 55 feet developed governs.
Check the existing 3/4-inch: about 130,000 BTU/hr at 40 feet - and less at 55 feet (roughly 110,000). The existing 120,000 BTU/hr of furnace plus water heater already saturates it; adding 65,000 puts the total at 185,000, roughly 40 percent over capacity. Tapping the 3/4-inch main would starve the furnace and the range simultaneously, showing up as delayed ignition, long recovery times, and nuisance pilot/ignition faults.
Sizing: at 55 feet developed with 185,000 BTU/hr connected load, 1-inch Schedule 40 black iron (about 200,000+ BTU/hr at that length in the standard low-pressure table - verify against the edition adopted) is the minimum; 1-1/4 inch gives margin. The alternative is a 2 psi system with a regulator at each appliance, which requires the purveyor's approval and is a larger scope change. Use the adopted table, not the table above, for the final number.
2. The owner wants to reuse a flexible appliance connector he has on hand to reach the range, and asks where the shutoff and sediment trap go. Answer both.
Read the worked answer
Connector: appliance connectors are listed in fixed maximum lengths, and 6 feet is the recognized maximum for a range connector. A longer connector is a violation even if it fits, because the connector is not a substitute for piping and is not protected against damage. Also:
- The connector must not pass through a wall, floor, ceiling, or cabinet partition.
- It must not be concealed and must be protected from physical damage.
- It must be listed for the appliance and sized for the load. If the run from the shutoff to the range exceeds 6 feet, run rigid pipe or CSST to within 6 feet and use a listed connector for the final connection.
Shutoff: a listed manual shutoff valve, of the plug or ball type (not a concealed-disk valve), installed in the same room as the appliance, accessible, and upstream of the connector. For a range, a standard gas cock in the supply line behind or beside the appliance is typical.
Sediment trap: required at the appliance, installed downstream of the shutoff and as close to the appliance inlet as practical, in the vertical drop of the piping, arranged so dirt and pipe scale fall into the leg instead of into the appliance's controls. On a range it goes in the drop to the connector, with a capped nipple forming the trap leg. Do not point the trap leg sideways or rely on a drip leg upstream of the valve.
3. The installer plans to use corrugated stainless steel tubing for the 15-foot kitchen run and asks about the pressure test and bonding. Outline the requirements and the judgment calls.
Read the worked answer
Bonding: CSST is a thin-wall stainless product and must be bonded to the premises grounding electrode system. The bonding conductor is typically 6 AWG copper minimum and must connect the gas piping to the grounding electrode system - not to a random plumbing pipe or a convenience outlet. Follow the tubing manufacturer's instructions, which in many cases are more specific than the general code rule, and remember that the appliance connector at the range is on the bonded system too.
Listing and installation: the CSST must be listed for fuel gas, protected from damage where it passes through framing or where it could be struck, and not concealed in a way that violates the listing. It must not be used where the manufacturer prohibits it (for example, in direct contact with certain materials).
Pressure test: test the new and existing piping as one system with the meter removed and all appliance valves closed, at the pressure the adopted code requires (commonly 1.5 times the maximum working pressure with a minimum on the order of 3 psi for low-pressure systems, held long enough for a stable reading - confirm the exact figure and duration in the edition your jurisdiction enforces). Use a calibrated gauge with a range appropriate to the test pressure, cap all outlets, and record the reading. Judgment call: do not accept a test where the gauge range is so large that a 1 psi drop is unreadable, and do not accept a test performed by watching a manometer on a system connected to the meter.