Propane Basics: What It Is and How It's Stored
Propane — also called liquefied petroleum gas (LPG) — is a hydrocarbon fuel derived from natural gas processing and crude oil refining. At normal atmospheric pressure and temperature, propane is a gas. Under moderate pressure, it becomes a liquid, which is how it is stored in your tank.
When you open a gas valve in your home, propane liquid at the bottom of the tank boils into gas vapor, flows through the regulator, through your gas lines, and reaches the appliance. The important implication: propane in your tank exists as liquid, but it is consumed as gas vapor. This is why pressure and temperature affect system performance — cold weather reduces the rate at which liquid propane vaporizes, which can reduce the pressure available to your appliances.
The Propane Tank
Your propane tank is a pressure vessel — a heavy steel container rated to hold propane under pressure. Residential tanks come in several standard sizes:
- 120-gallon (420 lb): Supplemental use — a single appliance or propane fireplace.
- 250-gallon: Smaller homes with limited propane load, or homes using propane for water heating and cooking only.
- 500-gallon: The standard size for most rural Colorado homes using propane for whole-home heating.
- 1,000-gallon: Large homes, whole-house generator setups, multi-building properties, and agricultural operations.
The tank's outer dome contains several components: the main shut-off valve (the hand wheel you can turn to close gas flow), the fill valve (where the delivery driver connects the supply hose), the pressure relief valve (a safety device that vents if internal pressure becomes dangerously high), and the float gauge (the dial that shows your percentage fill level).
Tanks are filled to a maximum of 80% capacity, leaving 20% as vapor space. This headroom is required because propane expands and contracts significantly with temperature — on a hot summer day, liquid propane expands enough that a completely full tank could develop dangerous pressure.
The Regulator
The regulator is the most critical safety component in your propane system. Propane exits the tank at relatively high pressure — typically 100–200 psi or more, depending on temperature and tank fill level. Your appliances require a consistent, much lower pressure — typically 11 inches of water column (about 0.4 psi) for most residential appliances.
The regulator's job is to step down the high tank pressure to the safe, consistent pressure your appliances need, regardless of how full the tank is or what the outdoor temperature is. A first-stage regulator handles the initial pressure drop from tank pressure to an intermediate level; a second-stage regulator (often located near the house) brings it down to appliance-level pressure. Some systems combine these into a single two-stage regulator at the tank.
The regulator has a vent — a small opening or screen on its side — that allows it to breathe and function properly. This vent must always be clear. Blocked vents from wasp nests (common in Colorado summers), ice, or debris are one of the most common causes of propane system failures.
Gas Lines and Distribution
From the regulator, propane travels through gas lines to your home and individual appliances. The main service line from the tank to the house is typically buried at least 12 inches deep (deeper below the frost line in climates like ours). Where buried lines emerge from the ground, they are usually protected with a riser and a shutoff valve.
Inside the home, distribution lines run through the walls, floors, and ceilings to reach each gas appliance. These interior lines are typically black steel pipe or CSST (corrugated stainless steel tubing) — both of which are rated for residential gas service.
Each appliance has its own dedicated shut-off valve — typically a quarter-turn ball valve or a manual shut-off — at the connection point. Know where each one is. If you need to shut off gas to a single appliance without cutting off the entire house, this is the valve to use.
Common Propane Appliances and Their Quirks
Forced-Air Furnace
A propane forced-air furnace operates on the same principles as a natural gas furnace. The burner ignites propane, heats a heat exchanger, and a blower moves air over the exchanger and through your ductwork. Modern furnaces use electronic ignition rather than a standing pilot. If your furnace will not ignite, check that the gas is on, the filter is not clogged, and the unit is not locked out on a fault code before assuming a gas supply issue.
Tankless and Tank Water Heaters
Tank-style propane water heaters have a standing pilot or electronic ignition and maintain a stored reserve of hot water. Tankless (on-demand) propane water heaters heat water only when a tap is opened, offering greater efficiency but requiring a higher BTU burner that demands adequate gas pressure. Homes converting from natural gas to propane should verify that their tankless water heater is properly configured for propane — BTU ratings and orifice sizes differ between natural gas and propane.
Propane Ranges and Cooktops
Propane ranges are set up with smaller orifices than natural gas ranges to compensate for propane's higher BTU content per cubic foot. A natural gas range that has been converted to propane (or vice versa) requires an orifice conversion kit — running a propane range on natural gas orifices (or natural gas on propane orifices) produces unsafe flame characteristics.
Propane Generators
Standby generators running on propane typically consume 2–4 gallons per hour at moderate load. A 500-gallon tank supporting a 20kW generator provides roughly 5–7 days of continuous runtime at average load — adequate for most power outage scenarios, but ranches or businesses using generators as primary backup during extended outages may benefit from a 1,000-gallon tank.