Determine the appropriate gas line size for your natural gas or propane appliances based on demand, length, and pressure.
Inputs
Natural Gas
Propane
Steel
Copper
Plastic (PE)
Enter values to calculate
Understanding Gas Line Sizing
Properly sizing a gas line is crucial for the safe and efficient operation of gas appliances. An undersized line can lead to insufficient gas pressure, causing appliances to perform poorly or even shut down. An oversized line is usually not a safety concern but can be an unnecessary expense. This calculator helps estimate the required inner diameter of a gas pipe based on key factors.
The Science Behind the Calculation
The calculation for gas line sizing typically relies on empirical formulas derived from fluid dynamics, most commonly based on the W. S. Wilson's formula or variations thereof. These formulas account for:
Total Gas Demand (BTU/hr): The sum of the heat input ratings of all appliances connected to the line.
Gas Type: Different gases (Natural Gas, Propane) have different specific gravities and energy densities, affecting flow characteristics.
Piping Length: Longer pipes create more resistance to flow.
Allowable Pressure Drop: The maximum acceptable reduction in gas pressure from the source to the appliance. Building codes often specify minimum pressure requirements for appliances, dictating the maximum allowable pressure drop. For natural gas, a common allowable drop is 0.5 inches of water column (w.c.).
Pipe Material: Different materials (steel, copper, plastic) have different internal surface roughness, affecting frictional losses.
The general principle is to find a pipe diameter that can deliver the required BTU/hr over the specified length with no more than the allowable pressure drop. This often involves using pre-calculated tables or iterative calculations that consider factors like gas velocity and friction loss.
How the Calculator Works
This calculator uses a simplified approach based on common industry standards and formulas. It takes your inputs and estimates the required Nominal Pipe Size (NPS) or the internal diameter.
Key Formulas/Principles Used (Simplified Explanation):
Determine Gas Properties: Based on the gas type, specific gravity and molecular weight are considered.
Capacity Tables/Formulas: The core of the calculation involves referencing or computing values based on tables or formulas like the ones derived from the Hardy cross method or Williams formula. These relate flow rate (BTU/hr), pressure drop, pipe length, and internal diameter.
Iterative Process: Often, the calculation might involve trying different pipe sizes until the required capacity is met within the allowable pressure drop.
Note: This calculator provides an estimate for informational purposes. Always consult with a qualified professional and adhere to local building codes and manufacturer specifications for final design and installation.
Example Calculation
Let's size a gas line for a typical home:
Total Gas Demand: A furnace (90,000 BTU/hr) and a gas range (60,000 BTU/hr) total 150,000 BTU/hr.
Gas Type: Natural Gas.
Piping Length: The longest run from the meter to an appliance is 75 feet.
Allowable Pressure Drop: We aim for no more than 0.5 inches w.c. drop.
Pipe Material: We'll use Steel pipe.
Plugging these values into the calculator will yield a recommended pipe size, which, for these inputs, might typically suggest a 1-inch or 1.25-inch diameter line, depending on the precise formula and internal diameter values used.
function calculateGasLineSize() {
var totalDemand = parseFloat(document.getElementById("totalDemand").value);
var gasType = document.getElementById("gasType").value;
var lineLength = parseFloat(document.getElementById("lineLength").value);
var pressureDrop = parseFloat(document.getElementById("pressureDrop").value);
var pipeMaterial = document.getElementById("pipeMaterial").value;
var resultDiv = document.getElementById("result");
if (isNaN(totalDemand) || isNaN(lineLength) || isNaN(pressureDrop) || totalDemand <= 0 || lineLength <= 0 || pressureDrop <= 0) {
resultDiv.innerHTML = "Please enter valid positive numbers for all inputs.";
resultDiv.style.backgroundColor = "#dc3545"; // Error color
return;
}
// Simplified values for specific gravity and internal diameters
// These are representative and may vary. Actual calculations use detailed tables/formulas.
var specificGravity = 1.0; // Default for Natural Gas
if (gasType === "propane") {
specificGravity = 1.56; // Propane specific gravity
}
// Internal diameters in inches for common NPS sizes
var internalDiameters = {
"steel": {
"0.5": 0.622,
"0.75": 0.824,
"1": 1.049,
"1.25": 1.380,
"1.5": 1.610,
"2": 2.067
},
"copper": { // Copper tube sizes are different
"0.5": 0.527, // Approx for Type L
"0.75": 0.745, // Approx for Type L
"1": 0.995, // Approx for Type L
"1.25": 1.245, // Approx for Type L
"1.5": 1.500, // Approx for Type L
"2": 1.900 // Approx for Type L
},
"plastic": { // HDPE / PE Pipe Sizes (SDR 11 is common)
"0.5": 0.560, // Approx
"0.75": 0.770, // Approx
"1": 0.970, // Approx
"1.25": 1.190, // Approx
"1.5": 1.420, // Approx
"2": 1.810 // Approx
}
};
var allowableDiameters = [];
// Iterate through common pipe sizes (NPS – Nominal Pipe Size)
// In a real-world scenario, a complex algorithm or lookup table would be used.
// This simplified loop checks a few common sizes.
var commonSizes = ["0.5", "0.75", "1", "1.25", "1.5", "2"];
for (var i = 0; i = totalDemand) {
allowableDiameters.push({ size: size + '" (NPS)', diameter: diameter });
}
}
if (allowableDiameters.length > 0) {
// Sort by smallest valid size first
allowableDiameters.sort(function(a, b) {
return parseFloat(a.size) – parseFloat(b.size);
});
var smallestValidSize = allowableDiameters[0].size;
resultDiv.innerHTML = "Recommended Minimum Pipe Size: " + smallestValidSize + "";
resultDiv.style.backgroundColor = "var(–success-green)";
} else {
resultDiv.innerHTML = "Could not determine a suitable size with these inputs. Consider larger pipe or consult a professional.";
resultDiv.style.backgroundColor = "#ffc107"; // Warning color
}
}