Propane Homes: What Every Trade Should Know

Why this matters

A propane home looks like a natural gas home from inside: the same furnace, water heater, range, and dryer, with slightly different orifices. Outside it is a different system with a different owner, a tank that runs out, and a gas that sinks instead of rising. Trades that do not know the difference relight an appliance after a run-out without a leak check, trench through an unmarked customer-owned gas line, or misdiagnose a starved furnace as a failed one. This card covers what every trade needs: how the system works, what to do when it leaks, who owns which part, and why an empty tank changes what happens next.

Propane in one paragraph

Propane (LP gas, liquefied petroleum gas) is stored as a liquid under its own vapor pressure. Appliances burn the vapor boiling off the top of the liquid. Tank pressure depends on temperature, not on how full the tank is: roughly 110 psi at 70 F and around 25 psi near 0 F. Two things follow. A cold tank delivers less vapor, so a small tank in deep cold can starve the appliances even with liquid left. And the gauge on the tank reads liquid level as a percent of capacity, not pressure. Tanks are filled to about 80 percent to leave room for the liquid to expand, so 80 percent on the gauge is full.

The parts between tank and burner

Inches of water column (in. w.c.) is the unit for low gas pressure: the height of water the pressure would push up a tube. About 28 inches of water column equals 1 psi. A propane appliance typically expects around 11 in. w.c. at its inlet; natural gas runs nearer 7, which is one reason propane and natural gas appliances use different orifices and regulator springs. The exact inlet and manifold figures for a given appliance are on its rating plate and in its installation manual.

Regulator vents. Each regulator breathes through a vent that must point down or be protected. A vent packed with ice, mud wasp nests, or a snow drift lets the regulator misbehave, which can mean high pressure at the burners or no gas at all. Lawn crews and snow removal crews should know never to bury or spray into a regulator.

The smell, and where the gas goes

Propane has no odor of its own. Suppliers add an odorant (commonly ethyl mercaptan) that smells like rotten eggs. Two limits on relying on the smell:

• Odor fade. The odorant can be absorbed by rust inside a new or poorly prepared tank or line, or oxidized away, so a real leak may smell weak or not at all.
• People. Some customers have a reduced sense of smell from age, illness, or medication. A listed propane gas detector, mounted low because the gas is heavy, is cheap protection worth recommending.

Propane is heavier than air. It pools in basements, crawlspaces, window wells, floor-level cabinets, and low spots outdoors, and it can lie there until it finds an ignition source. That is the opposite of natural gas, which rises. Ventilating a basement full of propane means getting it out at floor level, not opening an upstairs window.

When there is a leak

The safety action comes before any troubleshooting, every time, whether the tech is a gas fitter or a carpet cleaner:

1. Do not create a spark. No light switches, no phone calls, no unplugging anything, no starting a vehicle near the leak. Put out any flame.
2. Get everyone out, customers and pets included, and move uphill and upwind of the house or the tank.
3. Close the tank service valve only if you can reach it without passing through the gas: clockwise, hand-tight. If the smell is strong at the tank, leave it.
4. Call from a safe distance: 911 and the propane supplier. The supplier's number is usually on the tank or a tag.
5. Stay out until the supplier or fire department says the system is safe. Then, and only then, the system is leak-checked before any appliance is relit.

A trade that is not gas-qualified stops after step 5 and does not touch the gas system. A gas-qualified tech still waits for clearance before re-entering.

Who owns what, and who to call

Tank ownership. Many homeowners lease their tank from the propane supplier. A leased tank belongs to the supplier, and as a rule only that supplier fills it, by contract and in many states by law. Customer-owned tanks can be filled by any supplier willing to.

Responsibility split, in practice. The supplier generally answers for the tank, the service valve, and often the first-stage regulator and the line to the house. Interior piping and appliances belong to the homeowner, and work on them goes to a licensed or certified gas technician. Where the line runs underground, it may be supplier-owned or customer-owned; the free utility locate service (811) does not locate customer-owned lines. Ask the owner and the supplier before digging.

Licensing. Who may work on propane piping and appliances is a state matter. Some states license LP gas work separately from plumbing or HVAC; others fold it into a gas fitter or mechanical license. Check your state's fire marshal or LP gas board before sending a tech.

Why an empty tank needs a leak check before relighting

When a tank runs dry, more has happened than the furnace going out:

• Every pilot went out, and on older appliances with standing pilots the gas valve may still be in the "on" position. When gas comes back, those burners can release unburned gas.
• The system lost pressure, so a leak that was present all along may have been the reason the tank ran low faster than expected, and nobody would know.
• Air may have entered the lines, which has to be purged before appliances will light reliably.

That is why the fuel-gas codes require it. NFPA 54 (the National Fuel Gas Code, in the edition your state or local authority has adopted) requires that when gas is restored to a system after an interruption of service, the piping be checked for leakage immediately. NFPA 58, the propane storage and handling code most states adopt for the tank side, carries its own leak-check provisions in the edition your state adopted. On top of the code, many suppliers will not fill an out-of-gas tank unless a qualified person is present to perform the leak check, and some states write that duty onto the supplier directly.

The procedure itself, step by step, is its own SOP. See related: The Propane Out-of-Gas Relight SOP.

The customer who relit it themselves. If you arrive and the customer says they got a delivery and relit the pilots, ask whether anyone leak-checked the system. If not, tell them it should be done, and offer to do it if you are qualified. Write down that you advised it either way.

Worked example: a starved furnace that was not broken

A January call: propane furnace short-cycles and shuts down on a flame failure lockout, mostly in the early morning. Outdoor temperature near 0 F. The tank is a small vertical cylinder set, and the gauge reads 20 percent. The house also has a propane water heater and a gas fireplace.

The tempting answer. A flame failure lockout on a furnace of this age points at a dirty flame sensor or a weak igniter, and a tech could clean the sensor and leave.

What the tech measured instead. With the furnace off, a manometer on the furnace's inlet pressure tap reads 11 in. w.c. static. Furnace firing alone: 10.5 in. w.c. Then the owner runs the shower until the water heater fires and turns on the fireplace. With all three burning, the furnace inlet falls to 7 in. w.c. and the flame lifts and goes unstable; within two minutes the furnace locks out.

The reasoning. A healthy supply holds close to its static pressure under load. A drop from 11 to 7 in. w.c., which is more than a third, only when every appliance is on, at 0 F, with a small tank at 20 percent, says the tank cannot boil off vapor fast enough for the combined load. The furnace was the symptom, not the fault. A cleaned flame sensor would have passed a test run on a warm afternoon with nothing else firing and failed again the next morning.

What the tech did. Reset the furnace, confirmed it ran normally with only the furnace firing, cleaned the sensor anyway since it was coated, and called the supplier with the readings. The supplier scheduled a fill and an assessment of whether a larger tank was needed for this load.

What would have changed the answer. If the inlet pressure had dropped with the furnace alone, the cause is more likely in the line or regulator: an undersized or kinked line, or a failing or iced regulator. That is still a supplier or gas-fitter question, not a furnace part. If the gauge had read near 0 percent, the problem is a run-out, and the relight waits for a leak check.

Trade-specific notes

• HVAC. Confirm a furnace or boiler is set up for propane (orifices and gas valve spring), not natural gas. A natural-gas-orificed appliance on propane overfires and produces carbon monoxide.
• Plumbing. Propane water heaters relit after a run-out are covered by the same leak-check rule. Do not reconnect a gas water heater without a leak test of the connection.
• Electrical. Standby generators often run on the house propane supply and can drain a small tank fast during a long outage. Generator pads and trenches keep clear of the tank and line.
• Outdoor trades. Keep mowers, trimmers, pressure washers, and snow from striking or burying the tank, the regulator, or exposed copper tubing.

References

• NFPA 54, National Fuel Gas Code, Chapter 8 (leak checks after restoring service), in the edition adopted by your jurisdiction
• NFPA 58, Liquefied Petroleum Gas Code, in the edition adopted by your state
• Propane Education and Research Council (PERC), consumer and technician safety materials on leaks and odor fade
• Your state fire marshal or LP gas regulatory board, for licensing of propane work
• See related: The Propane Out-of-Gas Relight SOP; Rural Properties and the Self-Reliant Homestead