*Note: Calculations are based on 91,500 BTUs per gallon of propane and assume a max safe fill level of 80% capacity.
function calculatePropane() {
var tankSize = parseFloat(document.getElementById('tankSize').value);
var currentLevel = parseFloat(document.getElementById('currentLevel').value);
var btuRating = parseFloat(document.getElementById('btuRating').value);
var hoursUsed = parseFloat(document.getElementById('hoursUsed').value);
var pricePerGallon = parseFloat(document.getElementById('pricePerGallon').value);
if (isNaN(tankSize) || isNaN(currentLevel) || isNaN(btuRating) || isNaN(hoursUsed)) {
alert("Please enter valid numbers in all fields.");
return;
}
// Constants
var BTUS_PER_GALLON = 91502;
var MAX_SAFE_FILL_PERCENT = 80;
// Current status
var currentGallons = (tankSize * (currentLevel / 100));
// Usage logic
var gallonsPerHour = btuRating / BTUS_PER_GALLON;
var gallonsPerDay = gallonsPerHour * hoursUsed;
var daysRemaining = gallonsPerDay > 0 ? (currentGallons / gallonsPerDay) : 0;
// Refill logic (Tanks are usually only filled to 80% for expansion)
var maxGallons = tankSize * (MAX_SAFE_FILL_PERCENT / 100);
var gallonsNeeded = maxGallons – currentGallons;
if (gallonsNeeded < 0) gallonsNeeded = 0;
var refillCost = gallonsNeeded * pricePerGallon;
// Display
document.getElementById('currentGallons').innerText = currentGallons.toFixed(1);
document.getElementById('daysRemaining').innerText = Math.floor(daysRemaining);
document.getElementById('gallonsToFill').innerText = gallonsNeeded.toFixed(1);
document.getElementById('totalRefillCost').innerText = refillCost.toFixed(2);
document.getElementById('results-area').style.display = 'block';
}
Understanding Propane Usage and Tank Management
Managing your propane supply is critical for home heating, cooking, and powering appliances. Propane is stored as a liquid under pressure and expands into gas when released. Because of this expansion, propane tanks are never filled to 100% capacity; safety regulations typically limit the fill to 80% to allow for heat-induced expansion.
How Propane Consumption is Calculated
The standard unit of energy for propane is the British Thermal Unit (BTU). One gallon of propane contains approximately 91,502 BTUs of energy. To estimate how long your tank will last, you must determine the total BTU load of your appliances.
Gas Furnace: 40,000 to 100,000 BTUs/hr
Water Heater: 30,000 to 50,000 BTUs/hr
Gas Fireplace: 25,000 to 40,000 BTUs/hr
Kitchen Range: 30,000 to 65,000 BTUs/hr
Example Calculation
Suppose you have a 500-gallon tank with a gauge reading of 40%. Your furnace uses 80,000 BTUs per hour and runs for 5 hours a day.
Daily Usage: 0.87 x 5 hours = 4.35 gallons per day.
Run Time: 200 gallons / 4.35 = ~46 days of fuel left.
When Should You Refill?
Most propane providers recommend scheduling a delivery when your tank level falls between 20% and 30%. Letting a tank run completely dry is not only inconvenient but requires a professional leak test and pilot relighting service before the system can be put back into operation, which can be costly.
Pro Tip: Cold weather can cause the pressure in your tank to drop, sometimes leading to lower gauge readings even if the liquid level hasn't changed significantly. Keep your tank clear of heavy snow to allow sunlight to help maintain internal pressure.