Gas Line + Propane Sizing Reference
Why this matters
Gas + propane line sizing matters because customer's appliance won't perform if undersized + safety becomes critical if oversized OR wrong material. Wrong pipe = leaks = explosion. Right size + right material + proper installation per NFPA 54 = decades of safe operation. This is the field card.
Natural gas vs propane
| Parameter | Natural Gas | Propane |
|---|---|---|
| Heating value | 1,000 BTU/cu ft | 2,500 BTU/cu ft |
| Specific gravity | 0.6 (lighter than air) | 1.5 (heavier than air) |
| Supply pressure | 0.25 PSI (7" WC) | 0.5 PSI (14" WC) common |
| Manifold pressure | 3.5" WC | 10" WC (10 PSI tank) |
| Odorant | Mercaptan added | Mercaptan added |
Critical: propane sinks (accumulates in low spots, basements, crawl space); natural gas rises. Affects leak detection + venting.
Pipe materials
Black iron (steel) pipe: most common indoor + outdoor. Schedule 40. Threaded connections with pipe dope OR gas-rated PTFE tape (yellow).
CSST (Corrugated Stainless Steel Tubing): flexible, yellow OR black jacket. Common brands: Gastite, TracPipe, WardFlex. Faster install; bonding required to electrical service.
Copper Type L: residential interior natural gas (some jurisdictions). NOT for propane (sulfur in propane attacks copper).
Polyethylene (PE): outdoor buried gas service only. Yellow with tracer wire.
PVC: NEVER for gas (UV + temperature damage; not rated).
Sizing by demand + length
Total demand: sum BTU/hr of all appliances on the line.
Typical appliance demand: range top 65,000; oven 18,000; water heater (50 gal) 38,000; furnace (80,000) 80,000; dryer 35,000; fireplace 30,000; pool heater 250,000 - 400,000; residential generator 25,000 - 65,000 (all BTU/hr). Typical home total 200,000 - 350,000 BTU/hr.
Pipe size charts (natural gas 0.5 PSI delivery, 0.3" WC pressure drop)
| Length | 1/2" | 3/4" | 1" | 1-1/4" | 1-1/2" | 2" |
|---|---|---|---|---|---|---|
| 10 ft | 175 | 360 | 680 | 1,400 | 2,100 | 4,000 |
| 20 ft | 120 | 250 | 470 | 970 | 1,450 | 2,750 |
| 30 ft | 100 | 200 | 380 | 770 | 1,160 | 2,200 |
| 50 ft | 75 | 155 | 290 | 600 | 900 | 1,720 |
| 100 ft | 50 | 105 | 200 | 410 | 620 | 1,180 |
(Values in cubic feet per hour at 1,000 BTU/cu ft = cu ft × 1,000 = BTU/hr capacity)
Rule: longest single-appliance run determines pipe size for that segment.
Pipe size charts (propane 11" WC, 0.5" WC drop)
LP carries 2.5x heating value, so smaller pipe handles same BTU. Roughly 1/3 capacity of same-size natural gas pipe with same pressure drop.
Tank sizing (propane)
Tank vapor pressure 100 - 200 PSI depending on outdoor temp. Common residential tanks: 100-lb cylinder (23.6 gal LP / 2.4M BTU); 250 gal stationary residential heating; 500 gal large home/small commercial; 1,000 gal commercial/estate. Regulator stages: 1st (tank pressure → 10 PSI line), 2nd (10 PSI → 11" WC manifold).
Pressure regulators
Natural gas: utility delivers 7" WC; regulator only at meter (if utility delivers higher pressure).
Propane 1st stage: 100+ PSI tank → 10 PSI line. At tank.
Propane 2nd stage: 10 PSI → 11" WC. At each appliance OR at building entry.
Pressure regulator orientation: per manufacturer; vent line outdoors.
Common gas connections
Flexible appliance connector (yellow CSST OR stainless braid):
- 1/2" gas range (rated for 75,000 BTU)
- 1/2" water heater (rated for 50,000 BTU)
- 1/2" dryer (rated for 25,000 BTU)
- Maximum length 6 ft typical
- Approved fitting at each end (not damaged at install)
Hard-piped to appliance: required for fireplaces + some commercial; black iron + union for service.
Shutoff valve at each appliance: required by NFPA 54. Quarter-turn ball valve preferred.
Pressure testing
Per NFPA 54 + IRC:
Initial pressure test (rough-in, before drywall):
- Air OR nitrogen (NEVER oxygen)
- 1.5x working pressure OR 25 PSI (whichever higher)
- 30 minutes hold
- 0 PSI drop allowed
Final connection test:
- Soap solution at all joints
- Look for bubbles (leak detection)
- OR electronic gas leak detector
Pre-inspection: many jurisdictions require licensed plumber OR HVAC tech tag plus inspector sign-off before turn-on.
Joint sealing
Pipe dope (gas-rated): Rectorseal #5, Loctite 567, Permatex 80632. Approved per NFPA 54.
PTFE tape (yellow gas-rated): heavier density than standard white. NOT standard plumbing PTFE.
Compression fittings: at appliance connections; never on rigid line joints (vibration eventually leaks).
Bonding CSST
Required per NFPA 54 + manufacturer: CSST yellow jacket bonded to electrical service ground via min 6 AWG wire.
Failure to bond = lightning surge arcs through CSST = pinhole leak = fire.
Common gas line mistakes
Wrong PTFE tape (white vs yellow gas-rated). Pipe dope not gas-rated. Skipping pressure test (NFPA 54 violation). Mixing copper with propane (sulfur corrosion). Buried PE without tracer wire (can't locate later). CSST not bonded (lightning fire). Skipping shutoff valve at appliance. Undersized line (appliance starves; intermittent operation). Vent line from regulator inside building (leak inside instead of outdoors). Indoor regulator without proper vent.
Leak troubleshooting
Smell of gas:
- Open windows + evacuate
- Don't operate switches OR electrical
- Shut off at meter / tank
- Call utility OR licensed tech
Find with:
- Soap solution at joints
- Electronic detector
- NOT match / flame (obvious but mentioned)
Repair:
- Tighten joint with wrench (only if marginal)
- Replace fitting + re-dope (typical)
- Re-pressure test
Truck stock for gas work
Black iron pipe + assorted fittings (90s, tees, unions, plugs), yellow PTFE tape, gas pipe dope, leak detector solution, electronic leak detector, pressure-test gauge + caps, ball valves (1/2", 3/4"), flex connectors (gas-rated 24", 36"), CSST (if certified), bonding clamp + wire.
Gas tech certification
Most states require licensed plumber OR HVAC tech for gas work. Some require additional gas-fitter endorsement. CSST install often requires manufacturer training certificate (Gastite, TracPipe).
NEVER attempt to relight a pilot light OR turn on gas if you smell gas in the area. The proper sequence is: SHUT OFF GAS AT METER, EVACUATE, VENTILATE (open windows), do NOT operate light switches OR thermostats, do NOT use phones inside (call from outdoors), call utility OR licensed pro. Many gas explosions trace back to a homeowner trying to "just relight the pilot" with gas already accumulating in a room. The 30 minutes to ventilate + verify safe is worth it.
References
- NFPA 54 (National Fuel Gas Code)
- NFPA 58 (Liquefied Petroleum Gas Code)
- IRC Chapter 24 (Fuel Gas)
- IFGC (International Fuel Gas Code)
- Manufacturer technical data (Gastite, TracPipe, Rectorseal)
- Manuall internal: Water Pressure + Flow Reference, Soldering + Brazing