Propane fundamentals. Episode forty-nine of the Gas Service Animated series.

Propane is the shape-shifter of the fuel world: delivered as a liquid, stored under its own pressure, burned as a vapor. Every LP behavior a tech meets — the frost on a tank, the smell in a basement, the tiny orifices — falls out of a handful of numbers. Learn the numbers and propane stops surprising you.

Start at minus forty-four Fahrenheit — propane's boiling point. Any warmer than that, the liquid in the tank boils on its own, making vapor and pressure. That's why an outdoor tank needs no pump and no vaporizer for a house: the weather does the work. And it's why, at exactly minus forty-four, the pressure hits zero and the tank simply stops pushing.

Tank pressure follows temperature — not how full the tank is. The field chart: around zero p-s-i at minus forty-four. Twenty-eight at zero degrees. About one twenty-seven at seventy. Nearly two hundred on a hundred-degree day. Same tank, same fuel — the thermometer sets the gauge. That swing is exactly why the regulator story in this season has two stages.

Two specific gravities to carry. The vapor is one-point-five-two — half again heavier than air — so leaking propane sinks and pools: basements, crawlspaces, pits, ditches. You sweep low, the mirror image of natural gas. The liquid is point-five-oh-four — about four point two pounds a gallon — and it expands hard with temperature, which is a number you'll meet again at the fill valve.

One gallon of liquid makes about two hundred seventy gallons of vapor — two-seventy to one. Two consequences. A small liquid leak is a big gas event: a cupful of liquid is a room full of fuel. And liquid flashing to vapor steals heat so fast it freeze-burns skin on contact — treat liquid propane with glove-and-face respect.

The energy numbers explain the hardware. Propane vapor carries about twenty-five hundred Btu per cubic foot — two and a half times natural gas — and about ninety-one thousand five hundred Btu per gallon of liquid. Richer gas at higher pressure is why every LP orifice is smaller than its natural-gas twin, and why conversion kits exist at all — hold that thought for episode fifty-three.

The flammable range runs about two-point-one to nine-point-six percent in air — a much lower doorway than natural gas's five. Less propane in a space reaches ignitable, and a heavy vapor that pools doesn't dilute away on its own. The leak season's rules apply with the volume turned up: low sweeps, no ignition sources, and too-rich is never safe.

Propane is odorless; the smell is ethyl mercaptan, added at about a pound and a half per ten thousand gallons. And here's the LP-specific warning: mercaptan clings to bare steel and dies on rust — so odor fade is worst in brand-new tanks, rusty old ones, and after a system's been open to air. New install, out-of-gas restart, crusty container: never trust your nose alone. The instrument confirms.

Propane in one breath. Boils at minus forty-four; pressure follows temperature. Vapor sinks at one-five-two; liquid expands two-seventy to one. Twenty-five hundred Btu a foot, ninety-one thousand a gallon, flammable from two percent. And the smell can fade — confirm with the meter. Next: the containers.