How Do I Check If My LPG Bottle Is Empty or Still Has Gas?

Checking how much LPG is left in your gas bottle is something most NZ homeowners can do safely themselves using a few simple techniques. You don't need any special tools for the basic checks — just a bit of know-how and a healthy respect for gas safety. Here's what you need to know.

Why LPG Bottles Are Hard to Read

Unlike a petrol tank, LPG bottles don't have a built-in fuel gauge. LPG (liquefied petroleum gas) is stored under pressure as a liquid inside the cylinder, which makes it impossible to simply look inside. The gas you use is drawn off as vapour from the top of the liquid. This means the bottle can feel and look the same whether it's full or nearly empty — until it runs out at the worst possible moment.

Method 1: The Warm Water Trick (Most Reliable DIY Method)

This is the most popular and reliable method for homeowners:

1. Boil a kettle and carefully pour the hot water down the side of the bottle (not over the valve or fittings).
2. Wait about 30 seconds, then run your hand down the side of the bottle.
3. The metal will feel warm where there is only gas vapour, and noticeably cool or cold where liquid LPG is present.
4. The point where the temperature changes marks the approximate liquid level — that's how much gas you have left.

This works because the liquid LPG absorbs heat rapidly, cooling the metal wall of the bottle at that level. It's a well-established method used by tradespeople and homeowners alike.

Method 2: Weigh the Bottle

Every LPG cylinder has its tare weight (TW) stamped on the collar — this is the weight of the empty bottle. Standard NZ swap-and-go bottles (such as 9 kg cylinders) are clearly marked.

• Weigh your bottle on bathroom scales or a luggage scale.
• Subtract the tare weight from the total weight.
• The difference is approximately how many kilograms of LPG remain.

Example: If your bottle weighs 14 kg total and the tare weight is 8 kg, you have roughly 6 kg of gas left in a 9 kg bottle — about two-thirds full.

Method 3: LPG Level Indicator Strips

You can buy adhesive liquid crystal level indicator strips from hardware stores like Bunnings or Mitre 10. These stick to the outside of the bottle and change colour to show the approximate liquid level. They work on the same temperature-difference principle as the warm water method. They're a handy ongoing solution if you rely heavily on LPG.

Method 4: In-Line Gas Gauges

For a more permanent solution, inline pressure gauges or flow-through gauges can be fitted between the regulator and the bottle valve. These give a rough reading of remaining gas. Note that because LPG pressure stays relatively constant until the bottle is nearly empty, these gauges mainly alert you when you're running very low rather than giving a precise level throughout. Any modification to your gas system connections should be checked against your regulator and bottle setup — if in doubt, ask a licensed gasfitter.

Signs Your Bottle Is Running Low or Empty

• Appliances (BBQ, heater, hob) produce a weaker flame or cut out unexpectedly.
• The flame colour changes or becomes uneven.
• The bottle feels very light when you rock it gently.
• The warm water test shows the cool zone is at or near the bottom.

Safe Handling Tips

LPG is heavier than air and can pool at ground level, creating a fire or explosion risk if it leaks. Always follow these safety basics:

• Never use a naked flame to check the level.
• Store bottles upright and outdoors in a well-ventilated area, away from ignition sources.
• Check hoses and connections regularly for cracks or wear.
• If you smell gas, turn off the bottle valve immediately, ventilate the area, and don't operate any switches. Contact a licensed gasfitter or your gas supplier.
• For general gas safety guidance, refer to WorkSafe NZ.

LPG installations in NZ are covered under the Gas (Safety and Measurement) Regulations and the NZ Building Code. Your gas appliances and connections must comply with these standards.

When to Call a Professional

While checking your LPG level is a safe DIY task, any work on gas fittings, regulators, hoses, or appliance connections is restricted work under NZ law. This must be carried out by a licensed gasfitter registered with the Plumbers, Gasfitters and Drainlayers Board (PGDB). This includes:

• Replacing or adjusting regulators.
• Connecting or disconnecting appliances (other than routine swap-and-go cylinder exchanges on portable appliances such as BBQs).
• Repairing or replacing hoses and fittings.
• Installing new gas appliances.

Always ask to see your gasfitter's current practising licence before work begins. You can verify a tradesperson's licence on the PGDB website. If you need a qualified local gasfitter, you can search for one on tradedirectory.co.nz.

Sources & Further Reading

• WorkSafe NZ – Gas Safety
• Plumbers, Gasfitters and Drainlayers Board
• MBIE Building Performance – NZ Building Code
• Bunnings NZ – Gas Accessories
• Mitre 10 NZ
• BRANZ – Building Research