Calculate minimum nominal pipe diameter for Natural Gas and Propane systems
Natural Gas (0.60 S.G.)
Propane (1.50 S.G.)
0.5 in. w.c. (Standard)
1.0 in. w.c.
How to Size Gas Piping Correctly
Correct gas pipe sizing is critical for the safe and efficient operation of gas appliances. If a pipe is too small, the appliance will suffer from a pressure drop, leading to poor performance, soot buildup, or complete failure to ignite.
Key Variables in the Calculation
Total BTU/hr Load: The sum of the input ratings of all appliances connected to that specific branch or main line.
Longest Run: This is the distance from the gas meter (or regulator) to the furthest appliance in the system. Per code, you use this length for all sections to account for pressure drop across the entire system.
Specific Gravity (S.G.): Natural gas is lighter than air (approx. 0.60), while Propane is heavier (approx. 1.50). This significantly changes the flow capacity of a pipe.
The "Longest Length" Method
Professional installers typically use the "Longest Length" method derived from the International Fuel Gas Code (IFGC). To use this calculator, you should measure the distance of the furthest appliance and add roughly 10-20% to that length to account for the resistance caused by elbows, tees, and valves (equivalent length).
Warning: This calculator is for estimation purposes based on standard Schedule 40 metallic pipe tables. Local codes and specific material types (like CSST or Copper) may have different capacities. Always consult a licensed plumber or gas fitter.
function calculateGasPipeSize() {
var btu = parseFloat(document.getElementById("btuLoad").value);
var length = parseFloat(document.getElementById("pipeLength").value);
var sg = parseFloat(document.getElementById("gasType").value);
var drop = parseFloat(document.getElementById("pressureDrop").value);
var resultDiv = document.getElementById("gasResult");
var output = document.getElementById("resultOutput");
var details = document.getElementById("resultDetails");
if (!btu || !length || btu <= 0 || length <= 0) {
alert("Please enter valid positive numbers for BTU load and pipe length.");
return;
}
// Capacity Logic: Nominal sizes 1/2, 3/4, 1, 1-1/4, 1-1/2, 2
// We use a simplified Spitzglass approximation adapted for CFH (Cubic Feet per Hour)
// Conversion: CFH = BTU / (1000 for Nat Gas, 2500 for Propane)
var heatValue = (sg < 1) ? 1000 : 2500;
var cfh = btu / heatValue;
// Nominal Pipe Internal Diameters (inches) for Sch 40
var sizes = [
{ name: "1/2\"", id: 0.622 },
{ name: "3/4\"", id: 0.824 },
{ name: "1\"", id: 1.049 },
{ name: "1-1/4\"", id: 1.380 },
{ name: "1-1/2\"", id: 1.610 },
{ name: "2\"", id: 2.067 }
];
var recommendedSize = "";
var found = false;
// Formula: Q = 3550 * sqrt((h * d^5) / (S * L))
// Solving for capacity Q (CFH)
for (var i = 0; i = cfh) {
recommendedSize = sizes[i].name;
found = true;
break;
}
}
resultDiv.style.display = "block";
if (found) {
resultDiv.style.backgroundColor = "#d4edda";
resultDiv.style.border = "1px solid #c3e6cb";
resultDiv.style.color = "#155724";
output.innerHTML = "Recommended Size: " + recommendedSize + " Iron Pipe";
details.innerHTML = "Based on a flow requirement of " + Math.round(cfh) + " CFH and " + length + " ft total length.";
} else {
resultDiv.style.backgroundColor = "#f8d7da";
resultDiv.style.border = "1px solid #f5c6cb";
resultDiv.style.color = "#721c24";
output.innerHTML = "Size Exceeds 2\" Diameter";
details.innerHTML = "The load of " + Math.round(cfh) + " CFH is too large for standard 2\" residential piping at this length. Consider increasing pressure or using industrial sizing.";
}
}