.gas-rate-calculator-container {
font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
max-width: 800px;
margin: 0 auto;
background: #fff;
padding: 20px;
border-radius: 8px;
box-shadow: 0 2px 10px rgba(0,0,0,0.1);
}
.grc-header {
text-align: center;
margin-bottom: 30px;
background: #f0f7ff;
padding: 20px;
border-radius: 8px;
border-left: 5px solid #0066cc;
}
.grc-header h2 {
margin: 0;
color: #2c3e50;
}
.grc-grid {
display: grid;
grid-template-columns: 1fr 1fr;
gap: 20px;
}
@media (max-width: 768px) {
.grc-grid {
grid-template-columns: 1fr;
}
}
.grc-input-group {
margin-bottom: 20px;
}
.grc-label {
display: block;
margin-bottom: 8px;
font-weight: 600;
color: #333;
}
.grc-input, .grc-select {
width: 100%;
padding: 12px;
border: 1px solid #ddd;
border-radius: 4px;
font-size: 16px;
box-sizing: border-box;
transition: border-color 0.3s;
}
.grc-input:focus, .grc-select:focus {
border-color: #0066cc;
outline: none;
}
.grc-help {
font-size: 12px;
color: #666;
margin-top: 5px;
}
.grc-btn {
background: #0066cc;
color: white;
border: none;
padding: 15px 30px;
font-size: 18px;
font-weight: bold;
border-radius: 4px;
cursor: pointer;
width: 100%;
margin-top: 10px;
transition: background 0.2s;
}
.grc-btn:hover {
background: #0052a3;
}
.grc-results {
margin-top: 30px;
padding: 20px;
background: #f8f9fa;
border-radius: 8px;
display: none;
border: 1px solid #e9ecef;
}
.grc-result-row {
display: flex;
justify-content: space-between;
align-items: center;
padding: 10px 0;
border-bottom: 1px solid #eee;
}
.grc-result-row:last-child {
border-bottom: none;
}
.grc-result-label {
font-weight: 500;
color: #555;
}
.grc-result-value {
font-weight: bold;
font-size: 18px;
color: #2c3e50;
}
.grc-result-highlight {
color: #0066cc;
font-size: 24px;
}
.grc-tabs {
display: flex;
margin-bottom: 20px;
border-bottom: 2px solid #eee;
}
.grc-tab {
padding: 10px 20px;
cursor: pointer;
font-weight: 600;
color: #666;
border-bottom: 2px solid transparent;
margin-bottom: -2px;
}
.grc-tab.active {
color: #0066cc;
border-bottom: 2px solid #0066cc;
}
.grc-content {
margin-top: 40px;
line-height: 1.6;
color: #333;
}
.grc-content h3 {
color: #0066cc;
margin-top: 30px;
}
.grc-alert {
background: #fff3cd;
border: 1px solid #ffeeba;
color: #856404;
padding: 10px;
border-radius: 4px;
margin-top: 15px;
font-size: 14px;
display: none;
}
var currentTab = 'metric';
function switchTab(tab) {
currentTab = tab;
var tabMetric = document.getElementById('tabMetric');
var tabImperial = document.getElementById('tabImperial');
var divMetric = document.getElementById('metricInputs');
var divImperial = document.getElementById('imperialInputs');
var results = document.getElementById('resultsArea');
var error = document.getElementById('errorMsg');
results.style.display = 'none';
error.style.display = 'none';
if (tab === 'metric') {
tabMetric.className = 'grc-tab active';
tabImperial.className = 'grc-tab';
divMetric.style.display = 'block';
divImperial.style.display = 'none';
} else {
tabMetric.className = 'grc-tab';
tabImperial.className = 'grc-tab active';
divMetric.style.display = 'none';
divImperial.style.display = 'block';
}
}
function calculateGasRate() {
var errorDiv = document.getElementById('errorMsg');
var resDiv = document.getElementById('resultsArea');
errorDiv.style.display = 'none';
resDiv.style.display = 'none';
var kw = 0;
var btu = 0;
var flowRate = 0;
var flowUnit = ";
var volUsed = 0;
var volUnit = ";
if (currentTab === 'metric') {
var start = parseFloat(document.getElementById('metricStart').value);
var end = parseFloat(document.getElementById('metricEnd').value);
var time = parseFloat(document.getElementById('metricTime').value);
var cv = parseFloat(document.getElementById('metricCV').value);
if (isNaN(start) || isNaN(end) || isNaN(time) || isNaN(cv) || time <= 0 || cv <= 0) {
errorDiv.style.display = 'block';
errorDiv.innerText = "Please enter valid numbers for all fields.";
return;
}
volUsed = end – start;
if (volUsed <= 0) {
errorDiv.style.display = 'block';
errorDiv.innerText = "Final reading must be higher than initial reading.";
return;
}
// Metric Calculations
// Flow Rate m3/hr = (Volume * 3600) / Time
flowRate = (volUsed * 3600) / time;
// Heat Input kW = FlowRate(m3/hr) * CV(MJ/m3) / 3.6
// Note: Divide by 3.6 to convert MJ/hr to kW (since 1 kW = 3.6 MJ/hr)
kw = (flowRate * cv) / 3.6;
// Convert kW to BTU/hr
btu = kw * 3412.14;
flowUnit = 'm³/hr';
volUnit = 'm³';
} else {
// Imperial
var dial = parseFloat(document.getElementById('imperialDial').value);
var time = parseFloat(document.getElementById('imperialTime').value);
var cv = parseFloat(document.getElementById('imperialCV').value);
if (isNaN(dial) || isNaN(time) || isNaN(cv) || time <= 0 || cv <= 0) {
errorDiv.style.display = 'block';
errorDiv.innerText = "Please enter valid positive numbers.";
return;
}
volUsed = dial; // Volume for one revolution
// Imperial Calculations
// Flow Rate ft3/hr = (DialSize * 3600) / Time
flowRate = (dial * 3600) / time;
// Heat Input BTU/hr = FlowRate(ft3/hr) * CV(BTU/ft3)
btu = flowRate * cv;
// Convert BTU to kW
kw = btu / 3412.14;
flowUnit = 'ft³/hr';
volUnit = 'ft³';
}
// Display Results
document.getElementById('resKW').innerText = kw.toFixed(2) + ' kW';
document.getElementById('resBTU').innerText = Math.round(btu).toLocaleString() + ' BTU/hr';
document.getElementById('resFlow').innerText = flowRate.toFixed(3) + ' ' + flowUnit;
document.getElementById('resVol').innerText = volUsed.toFixed(4) + ' ' + volUnit;
resDiv.style.display = 'block';
}
Gas Rate Calculator (Heat Input)
Calculate the gross heat input and gas flow rate for natural gas appliances.
Metric Meter (m³)
Imperial Meter (ft³)
Reading at start of test
Reading after timed period
Usually 120 seconds (2 mins)
Standard UK approx 39.0 – 40.0
1 ft³ per revolution
½ ft³ per revolution
2 ft³ per revolution
5 ft³ per revolution
10 ft³ per revolution
Capacity of the test dial used
Standard Natural Gas approx 1030-1040
Please enter valid positive numbers. For Metric, ensure End Reading is greater than Initial Reading.
Results
Gross Heat Input (kW):
–
Gross Heat Input (BTU/hr):
–
Gas Flow Rate:
–
Volume Consumed:
–
What is Gas Rating?
Gas rating is a critical procedure performed by gas engineers to determine the actual heat input of a gas appliance, such as a boiler, furnace, or water heater. By measuring the volume of gas consumed over a specific time period at the meter, you can calculate the energy being delivered to the appliance.
How to Calculate Gas Rate (Metric Meters)
Most modern installations use metric meters measuring in cubic meters (m³). To calculate the rate:
- Ensure all other gas appliances are turned off.
- Turn the appliance being tested to its maximum setting.
- Note the initial reading on the meter (including 3 decimal places).
- Time a specific period (usually 120 seconds / 2 minutes).
- Note the final reading.
- Calculate the volume used (Final – Initial).
- Formula: Heat Input (kW) = (Volume (m³) × 3600 × Calorific Value) / (Time (sec) × 3.6).
How to Calculate Gas Rate (Imperial Meters)
Older installations may use imperial meters measuring in cubic feet (ft³). These typically have a test dial.
- Identify the test dial (usually marked 1 ft³, 2 ft³, etc.).
- Time exactly one full revolution of the dial in seconds.
- Formula: Gas Rate (ft³/hr) = (Dial Size × 3600) / Time (sec).
- Heat Input: Convert the rate to BTUs using the Calorific Value (approx 1037 BTU/ft³) and then to kW (divide BTU/hr by 3412.14).
Why is this calculation important?
Calculating the gas rate ensures an appliance is burning the correct amount of fuel.
- Under-gassed: The appliance may run inefficiently, fail to reach temperature, or condensate excessively in the flue.
- Over-gassed: This is dangerous. It can lead to incomplete combustion, production of Carbon Monoxide (CO), and overheating of components.