Gas Pipe Sizing Calculator

Calculate the correct pipe size for natural gas and propane systems based on BTU load, pipe length, and allowable pressure drop per NFPA 54 (National Fuel Gas Code) standards.

⚠️ Important Safety Notice

• This gas pipe sizing calculator provides general estimates only based on typical assumptions.
• Gas piping must comply with local building codes and fuel gas regulations.
• Always verify results with a licensed gas fitter or engineer before installation or modification.
• Improper gas piping can cause fires, explosions, and carbon monoxide poisoning.
• All installations must be pressure tested and inspected per NFPA 54.

Gas Pipe Sizing Parameters

Gas Type *

Natural gas: 1000 BTU/CFH | Propane: 2500 BTU/CFH

Total BTU Load (BTU/hr) *

Total BTU/hr of all appliances on this gas line

Pipe Length (feet) *

Straight pipe length. Add 5 ft per 90° elbow, 2 ft per tee.

Allowable Pressure Drop (inches WC) *

Residential typically uses 0.5" WC pressure drop

Sizing Results

Enter parameters and click Calculate to see results

Legal Disclaimer: This calculator provides estimates based on NFPA 54 (National Fuel Gas Code) capacity tables for Schedule 40 black iron pipe. Results are for straight pipe runs only and do not account for fittings, elevation changes, or unusual conditions. All gas piping installations must be designed and installed by licensed professionals following local codes, NFPA 54, and manufacturer specifications. The user assumes all responsibility for proper application and verification of results.

How to Use This Gas Pipe Sizing Calculator

Input Parameters:

1. Gas Type

Select either Natural Gas or Propane (LP). Natural gas has a heating value of approximately 1,000 BTU per cubic foot (CFH), while propane has approximately 2,500 BTU per CFH. This difference significantly affects the required pipe capacity.

2. Total BTU Load

Enter the total BTU/hr rating of all gas appliances that will be supplied by this pipe run. For example, if you're installing a 40,000 BTU/hr furnace and a 30,000 BTU/hr water heater on the same line, enter 70,000 BTU/hr. Always use the appliance nameplate ratings.

3. Pipe Length

Enter the straight pipe run length in feet from the gas meter or tank to the farthest appliance. For fittings, add equivalent lengths: approximately 5 feet per 90° elbow, 2.5 feet per 45° elbow, and 2 feet per tee fitting. For example, a 50-foot run with three 90° elbows would be entered as 65 feet (50 + 15).

4. Allowable Pressure Drop

Select the maximum allowable pressure drop in inches of water column (WC). Residential installations typically use 0.5" WC, which is the most conservative option. Commercial installations may use 1.0" or 3.5" WC for longer pipe runs, but this must be verified with local codes and the gas supplier.

Understanding the Results:

The calculator provides a recommended pipe size based on NFPA 54 capacity tables for Schedule 40 black iron pipe. It automatically applies a 10% safety factor to account for future expansion and conservative design practice. The results include:

Recommended Pipe Size: The smallest pipe diameter that safely meets your requirements
Required Flow Rate: The cubic feet per hour (CFH) needed for your BTU load
Pipe Capacity: The actual CFH capacity of the recommended pipe at your specified conditions
Pipe Utilization: How much of the pipe's capacity you're using (ideally below 90%)
Estimated Velocity: Gas flow velocity in feet per second (should be below 60 fps for natural gas)
Capacity Reference Table: Comparison of all available pipe sizes for your conditions

About Gas Pipe Sizing

Why Proper Gas Pipe Sizing Matters

Correct gas pipe sizing is critical for safety, performance, and code compliance. Undersized pipes can cause insufficient gas flow to appliances, leading to incomplete combustion, reduced efficiency, appliance damage, and potential carbon monoxide production. Proper sizing ensures:

Adequate gas pressure at all appliances for proper operation
Prevention of appliance malfunction and damage
Safe combustion with minimal carbon monoxide risk
Compliance with NFPA 54 and local building codes
Passing required inspections
Future expansion capacity

NFPA 54 Standards

NFPA 54, also known as the National Fuel Gas Code, provides comprehensive standards for the design, installation, and operation of fuel gas piping systems. This calculator uses capacity tables from NFPA 54 Tables 402.4(2), 402.4(5), and 402.4(8) for natural gas, and equivalent propane tables.

The tables are based on specific assumptions including:

Schedule 40 black iron pipe (standard for gas installations)
Natural gas specific gravity of 0.60 (relative to air)
Propane specific gravity of 1.50 (relative to air)
Pressure drops of 0.5", 1.0", or 3.5" water column
Straight pipe runs (fittings require equivalent length additions)
Standard temperature and pressure conditions

Pipe Materials for Gas Service

Schedule 40 black iron pipe is the most common and widely accepted material for natural gas and propane installations. It's durable, code-compliant, and compatible with all gas types.

Other approved materials include:

CSST (Corrugated Stainless Steel Tubing) - requires manufacturer-specific sizing
PE (Polyethylene) pipe - outdoor underground use only, natural gas only
Copper - limited applications, check local codes

Never use: PVC, CPVC, galvanized steel (interior threading damage), or regular copper tubing designed for water. Always verify material compatibility with local codes.

Common Sizing Scenarios

Typical Residential (Natural Gas)

150,000 BTU/hr load, 60 ft run, 0.5" WC drop → Recommended: 3/4" pipe

Covers furnace (100k BTU) + water heater (40k BTU) + range (10k BTU)

Small Commercial (Natural Gas)

500,000 BTU/hr load, 100 ft run, 1.0" WC drop → Recommended: 1-1/2" pipe

Restaurant equipment or multiple commercial appliances

Residential Propane

100,000 BTU/hr load, 50 ft run, 0.5" WC drop → Recommended: 1/2" or 3/4" pipe

Typical for rural homes with propane tank

Code Requirements & Safety Guidelines

Professional Installation Required

Gas pipe installation is not a DIY project. All gas piping must be installed by licensed, qualified professionals in accordance with:

NFPA 54 (National Fuel Gas Code) - National standard
International Fuel Gas Code (IFGC) - Adopted by many jurisdictions
Local Building Codes - May have additional requirements
Utility Company Requirements - Gas supplier specifications
State/Provincial Regulations - Licensing and permit requirements

Inspection and Testing

All gas piping installations must undergo:

Pressure Testing: Typically 1.5 times operating pressure for 30-60 minutes minimum
Leak Testing: Using approved leak detection solution or electronic detector
Building Inspection: Required before gas service activation
Final Inspection: By utility company before meter connection

Critical Safety Warnings:

• Gas leaks can cause fires, explosions, and death
• Improper installation can produce carbon monoxide (odorless, deadly)
• Never work on gas lines without proper training, licensing, and permits
• Always shut off gas supply before any work
• If you smell gas (rotten egg odor), evacuate immediately and call emergency services
• Natural gas is lighter than air; propane is heavier (sinks to low areas)

Common Code Violations to Avoid

Using undersized pipe (insufficient capacity)
Using unapproved pipe materials (PVC, galvanized, etc.)
Inadequate pipe support and bracing
Improper joint sealing (use yellow gas-rated thread sealant or tape)
Missing or incorrect sediment traps (drip legs)
Inadequate appliance shutoff valves
Pipes passing through concrete without sleeves
Insufficient clearance from electrical components
Missing or incorrect labeling