Cost of running instantenous LPG water heater

Am trying to buy an Thermann hot water system running LPG . How you can I have some sort of idea of how much this going to cost.

It will be 26l /mn unit using LPG for 3/4 people. The unit is said to be using 176M/j and the bottle/large cylinder of LPG is around $140 in Northern NSW.

The water is to used for washing up and showers.
Does anyone have some experience with these sorts of units?

We do have a Stiebel heat pump and it uses around $980 a year. It is very noisy machine. And it store 300l of water which we hardly use.

Thanks in advance


We have a Bosch instantaneous gas HW on LPG. Similar flow rate. We also have a gas oven/cooktop. We cook nearly all our meals at home.

With two and occasionally three people a large bottle of gas $140 lasts around 5 months. Add $30pa bottle rental and it adds up to less than $400 a year.

Our experience with a similar setup with a storage gas fired HW suggests these are less effecient although they cost less to buy and install.

Have you also considered Rinnai and Bosch as alternate brands?

Just note that all come temperature limited to 50C or 55C as standard and cannot be set higher. National standard and plumbing police so no one gets burnt by hot water. They need to be close to your bathroom and kitchen if possible. It also helps to have properly lagged HW piping.


After looking at the Product Review website, neither the Stiebel heat pumps or the Thermann gas continuous flow units are very highly rated.

Perhaps, as mark_m suggested, have a look at the Bosch and Rinnai units.

We installed a Saxon heat pump at our previous residence and it was fantastic. It cut our electricity usage for hot water by 80% and the hot water bill by 70%, but unfortunately Saxon are no longer trading.

Our current home in Cairns has a Conergy solar system which occasionally uses a few Kwh during rainy or overcast periods. Otherwise, the hot water is free.


Thank you to Mark and Fred for their input. Mark, you are in the same position as we are.

Will definitely look at Rinnai or Bosh. Had a Bosh when we were living in Melbourne, but that was many moons ago.

Thermann (Reece plumbing brand) has a new one out C7 which is a condensing heating system and has 7 stars rating.

Thanks to Mark for giving these figures. Very helpful indeed. That is what I estimated while discussing it with my husband.

Will make sure the plumber will lag the pipes also very important.

Going to have to make a move pretty soon…we are not “in hot waters” at the moment.


Years ago, not sure it has been resolved by the manufacturers, but some of the instant gas hot water systems required a minimum flow rate to activate water heating. It may be worth asking this as well as the maximum flow rates, especially if you have (very) low flow devices installed in your house (e.g. low flow taps or shower rose).


Yes, it is an interesting point to remember indeed. We are on tank water …hence activated by a pump. We do get a good pressure from the pump.

We are thinking at this stage to get either the Rinnai 20 or the Bosh C21 highflow. Just weighing the 2.

Asking around for prices and insallation costs.


Do not confuse pressure with flow rate. It appears the lowest flow that will trip on a particular Rheem is about 2.0 lpm. Some units require much more. Depending on one’s water habits that could be irritating if you, for example, run a drizzle of hot water whilst washing up. The drizzle would need to be a stream for 2.0 lpm if that makes the point.


I had a Rinnai “instantaneous” LPG water heater for 13 years, I now have solar. A few points:

  • It isn’t as instantaneous as you might like, even with the lines to common use points (bathroom, kitchen) quite short it takes a while to turn on, heat up and for the hot water to come through. This is OK for a shower or a sink full of water but not for a bit to wash your hands when the cold water line is barely above zero as the delay is excessive and so is the waste. If you are used to filling a cooking pot with hot water and then another 5 minutes later, you don’t get the continuity of hot water in the line because while it turns on and re-heats it is pushing cold water to your tap each time not hot as with a tank.

  • The price of gas is likely to go up, some say much faster than CPI. This is due to complexities of the gas industry rather than shortage of gas.

  • The setup for the Rinnai requires the gas line, mains power and a control line, so both plumber and sparky are required.

  • The aggregate weight of a 45kg cylinder is 60+kg, you will need a hand truck and a strong back unless it is going to be delivered and swapped for you. Technically speaking you shouldn’t transport them lying down at all, they are supposed to stand up which isn’t possible unless you have a truck or open ute with a cage or bracket to restrain it. This rule is often ignored but that’s up to you.


The exact details and trades and costs for installing a new HW service will not be the same in every circumstance. It may be prudent to seek quotes specific to your own property to be sure before any decision is made. There may be added costs for any system depending on the age of your property necessary to meet current code or council requirements. It is always best to ask your plumber. Ours has to answer me twice, once to explain it and a second time so that I understand it.:brain:

We had a storage HW before the instantaeous gas HW. There was no noticable difference to the delay in getting hot water to the sink or shower for our plumbing layout.

The hot water if not run in the previous 5-10 minutes also needs to heat up the pipe work along the way. Typically there is always some cold water loss regardless of the type of HW system you use. There are ways to recover some of this water if you choose. Eg collect in bucket for garden. Washing hands with cold water is life, warm water is a waste.

Our current Bosch HW plugs into a standard 240v socket to power the controller which is built in and the ignition circuit. There was no other wiring needed. Even a solar hot water may need an electrician for the install if it uses a circulation pump.

There is mention of a Bosch option for our instantaeous HW that uses a battery or low voltage supply and no mains wiring.

I’m not aware of any one who exchanges 45 kg capacity LPG bottles other than through home delivery. It is part of the service. Our supplier is based 40 km distant. Each LPG provider needs to keep control of their bottles for safety reasons. There are also code requirements on how the bottles are transported and installed.

The cost of LPG for domestic use may go up more than Inflation or CPI, but to date electrical power is no different. It’s true Australia is LPG blessed. We considered evacuated solar. For us that was a very long payback on that option. We would still need to purchase or use a backup for boosting during extended wet or cloudy periods with electric or gas or a wood burner. Given we cook on gas it seemed pointless going to solar HW. Secondly for a lesser investment we are able to install solar PV that provides twice our daily electrical usage and does have a payback.

One other consideration for our install is that we do not have town water. Our tertiary treatment is through inline UV sterilisation. There is no residual protection through chlorination of our water, so we prefer to minimise dead storage in our plumbing.

p.s. we have also previously lived away from the coast for many years with a rooftop solar HW. Despite being rain poor and sun rich it still needed electricity for boosting with a family of 5. It also proved to be reliable other than for hail stones golf ball size and above. Hopefully current options can withstand cricket balls, based on more recent weather events.


Well, after all the great input from everyone above and many thanks to all, we have decided to get the Bosh 21l/mn which will be ample for our needs. It is a condensing unit, so hopefully in real life this would be efficient heating.
We had some very informative input also from ELgas staff in Lismore (NSW) and got also all sorts of tips to connect gas to our existing bottles.

The plumber has been contacted and if all goes well next week we shall have a decent shower…I am not implying that we have not washed…we have a granny flat which is empty and it has a hot water system. So, we have not been without a shower,(LOL) but no hot water for washing up.

Again thanks to all for your input and also to CHOICE.