45 kg LPG bottles: hot-water costs and how long they may last

Confirm a nominal 45 kg bottle and use the ongoing refill price from the supplier or bill. A new-customer offer, deposit or combined first-delivery package may not represent the next refill. HotWaterWise supplies no indicative bottle-price default because a sufficiently comparable local ongoing price has not been established.

Record whether delivery is included, collected, separately charged or unknown. For a separate delivery fee, also record the number of bottles in the order. Keep annual rental or service charges separate. Unknown charges are excluded and labelled unknown; they are not treated as confirmed free service.

The bottle-energy conversion uses 49.6 MJ/kg of propane gross energy from Australian Energy Statistics, Table 9. A nominal 45 kg fill therefore represents 2,232 MJ of fuel energy. Appliance efficiency is applied separately, once, to work out how much fuel supplies the required water heat.

At 150 litres/day of 60°C-equivalent demand, the model needs 2,482.82125 kWh of useful heat a year. For instantaneous gas at the 0.78 planning efficiency, fuel input is 2,482.82125 × 3.6 ÷ 0.78 = 11,459.175 MJ/year. Dividing by 2,232 gives 5.134 bottle-equivalents a year.

At that constant hot-water-only demand, one nominal fill represents roughly 71 days. This is an annual-average illustration, not a delivery forecast. Other appliances, colder inlet water and changing demand can shorten that interval. The model does not round fractional bottles up into purchases or delivery orders.

Use hypothetical inputs of $150 per refill, a $20 delivery fee covering two bottles and $100 annual rental. These are illustrative entered amounts, not supplier quotes or Brisbane price averages. Retain the instantaneous-system demand above.

• Fuel: 5.134038978… × $150 = approximately $770.11/year.
• Delivery: $20 ÷ 2 = $10 per bottle-equivalent, or approximately $51.34/year.
• Hot-water usage cost including delivery: approximately $821.45/year. Hot Water Cost displays $821/year and $68/month.
• If hot water is the only LPG use and all these charges are confirmed, including $100 rental gives approximately $921.45/year for that service.

The calculation uses unrounded bottle-equivalents throughout. Delivery is already included in the usage-cost figure; adding it again to a replacement comparison would overstate savings.

Replacing the water heater may leave LPG connected for a cooktop or heater. In that case, annual rental is not an avoided hot-water replacement cost. HotWaterWise adds entered rental to eligible replacement savings only when LPG discontinuation is confirmed. Cancellation or bottle-removal costs need a separate quote.

The Electric vs Gas calculator keeps its usage-cost comparison separate from fixed-charge information. Hot Water Cost can carry the relevant submitted details into Payback. Check the charge labels rather than treating all results as a whole-household gas bill.

Only the supported 45 kg bottle basis is modelled. Other cylinder sizes and bulk tanks require different evidence. Read Methodology for the complete LPG rules, or continue to the heat-pump guide when considering replacement.