Propane Vaporization Rate Calculator
*This is an estimate based on "wetted surface area" at the specified fill level and temperature.
How Propane Vaporization Works
Propane is stored in tanks as a liquid under pressure. For your appliances to function, that liquid must "boil" and turn into a gas. This process is called vaporization. Because the boiling point of propane is -44°F, it naturally vaporizes at most Earth temperatures, but it requires heat from the surrounding air to do so.
The rate at which a tank can generate gas depends on three primary factors:
- Wetted Surface Area: Only the part of the tank in contact with liquid propane can effectively transfer heat from the outside air to vaporize the fuel. As the tank gets lower, the vaporization rate drops significantly.
- Ambient Temperature: The colder the outside air, the less heat is available to boil the propane.
- Tank Size: Larger tanks have more surface area and can therefore vaporize more gas per hour than smaller tanks.
The Vaporization Formula
The standard industry formula used by this calculator is:
BTU/hr = Area × (Ambient Temperature – Boiling Point) × K-Factor
Where:
- Area: The wetted surface area (sq. ft.) based on the tank dimensions and fill percentage.
- Boiling Point: -44°F for propane.
- K-Factor: A heat transfer coefficient (usually 2.0 to 3.5 depending on humidity and frost conditions).
Calculation Example:
Imagine a 500-gallon tank at 40% full on a 30°F day.
1. Total Surface Area of 500-gal tank: ~95 sq. ft.
2. Wetted Area (40%): 38 sq. ft.
3. Temperature Delta: 30°F – (-44°F) = 74 degrees.
4. Estimated Output: 38 sq. ft. × 74 × 2 = 5,624 BTU/hr (Continuous withdrawal).
Why Does This Matter?
If your total appliance load (Furnace + Water Heater + Stove) exceeds the vaporization rate of your tank, the pressure inside the tank will drop. This leads to weak flames, appliance lockout, or "nuisance" service calls, even when you still have 20% fuel left in the tank. This is especially common during extreme cold snaps when the temperature delta is low.