Installation guide
58 | Rinnai Continuous Flow Water Heating Specication Guide 02-13
We often get asked about how long a gas bottle will last when running a gas appliance. Using the
calculation below you can work this out yourself.
LPG gas bottle energy calculation
1 kg of LPG gas contains 50.4 MJ of energy
1 kW = 3.6 MJ
This means that a 45 kg LPG gas bottle has:
45 kg x 50.4 MJ = 2268 MJ
This works for the different bottle sizes, here are the most common:
9 kg = 453.6 MJ
45 kg = 2268 MJ
twin pack = 4536 MJ (two 45 kg bottles)
Calculating how long an LPG bottle will last
To work out how many hours an LPG gas bottle will last, you need to divide the energy (MJ) by the total MJ input
of your appliance (in MJ/h).
For example, here are some approximate running times for a few of Rinnai's heating products:
Rinnai Portable Convector: Avenger = 2268 ÷ 25 (MJ input of appliance on high)
= 91 hours (approximately)
Rinnai Energysaver
®
: 309FT = 2268 ÷ 13 (MJ input of appliance on high)
= 174 hours (approximately)
Rinnai Gas Fireplace: Arriva = 2268 ÷ 31.5 (MJ input of appliance on high)
= 72 hours (approximately)
The input figures used in the above calculation are when the appliance is running on high. It is rare that you will
run the appliance on high for a long period of time, so the above usage calculation will be the worst case scenario.
A continuous flow water heater has a slightly different calculation as usage is normally intermittent. You can still
use the calculation, you just need to determine how long the unit will be used each day, i.e. the shower is used
three times each day for approximately five minutes, there are two loads of washing done each day, and there is
intermittent use of the kitchen tapequates to 30 minutes of continued use each day.
Approximate running time based on the above example:
Rinnai Infinity VT26 = 2268 ÷ 199 (MJ input of appliance on high)
= 11 hours (approximately)
= 660 minutes ÷ 30 minutes equates to 22 days per 45 kg bottle
Appendix 4: LPG gas bottle consumption