What is propane vapor pressure?
Vapor pressure is the force exerted by propane gas molecules against the walls of a tank, which rises with temperature and determines whether gas can flow to appliances.
The pressure inside a propane tank depends on how much of the propane has evaporated into gas form. This gaseous pressure is vapor pressure, and it increases when temperature rises. A propane tank at 70 degrees Fahrenheit holds roughly 100 pounds per square inch (psi) of vapor pressure, while the same tank at 100 degrees might reach 200 psi or higher. This relationship between heat and pressure is consistent and predictable for propane.
Vapor pressure matters directly to how your equipment operates. A regulator needs sufficient vapor pressure to push gas through the lines and into an appliance. When a tank sits in cold weather, vapor pressure drops. In northern Florida winters or during extended cold snaps, tanks left outdoors may develop low vapor pressure that cannot overcome regulator resistance, causing appliances to shut down or fail to ignite. This is why propane suppliers sometimes recommend keeping tanks in slightly warmer locations during winter or using tanks with higher liquid content reserves.
For propane businesses serving Florida, understanding vapor pressure also informs tank placement advice and regulator sizing. A regulator designed for 100 psi will work fine in normal conditions but can cause flow problems if vapor pressure drops below its minimum threshold. Suppliers need to account for seasonal temperature swings when helping customers choose equipment that will perform reliably year-round, even during occasional cold fronts.