Changing from Regular Gas Hot Water to Continuous Hot Water

Has anybody here replaced a normal gas hot water service with a continuous one like a Rinnai Infinity? If so, was it difficult and/or expensive? My children are 21 and 19. The 21 yo's partner lives with us and the 19 yo's partner is here probably 4-5 nights per week. Our hot water service is struggling to keep up even with some of them showering the night before. We still often have 3 adults wanting showers in the morning.


  • +17

    Sounds like you have a freeloader problem, not a hot water problem.

    • +13

      Yeah - but they're all good kids who pitch in with the housework and they all seem to get along well with us and each other :)

  • +2

    If the existing gas water heater is over 10 years old, this is probably a good plan anyway before the old one carks it.
    You need to choose a big continuous water heater to get a good flow for showering (the smaller ones are only good for filling sinks for washing up).
    This requires a bigger flow of gas, so the pipe from the meter to the heater will probably need increasing from 1/2" to maybe 1".
    Another consideration with a continuous gas water heater is the range of flow over which the heater will operate. Some of the older models will only heat the water when the flow is at maximum so if you just have a trickle flowing to wash your hands in a sink, the heating shuts off. Most of the later models are very much better and will heat water at both high and low flow rates.
    Cost? Maybe $1,500 installed. Shared out between you and four kids, that's only $300 each…

    • It's about 14 years old, so is probably definitely on the way out. The dishwasher has just died and that was the same age. Thanks for the info :)

      • +2

        Special note when selecting they are usually shown with one Flow rate The specifications of an Infinity 16 are 16 Litres minute;
        but this is not the full story.

        must read manual to determine the one for you. (Additionally The unit can only deliver as fast as the cold water comes from the street.)
        Max Flow / Temperature Rise
        16L / 25C
        This means if it is 10C outside the device will rise that temperature up by 25C (35C output) at a rate up to 16 Litres per minute

        However I would want 45C output therefore I would experience 10L / 40C;
        10 litres minute more that adequate for me, but home 2 bathrooms + washing machine will struggle at times.

        I replaced all my tanks with instant and it is great 10L is more that sufficient for Tap and Shower at same time without temperature drop.
        due to their reduced density value is gained putting separate ones each space kitchen/bathroom/laundry reducing heat losses and temperature variation of water travelling long runs to taps.

    • kmwa knows what he's talking about. We had our gas hot water (storage system) die a few years ago and had to replace it.

      if the existing gas water heater is over 10 years old, this is probably a good plan anyway before the old one carks it.

      We went at least a week without hot water.

      You need to choose a big continuous water heater to get a good flow for showering (the smaller ones are only good for filling sinks for washing up).

      Most/all instantaneous systems are rated for a particular flow rate with set temperature difference (litres per minute @ xx°C rise). So at maximum flow, it is only designed to raise the temperature of the water by xx°.

      This requires a bigger flow of gas, so the pipe from the meter to the heater will probably need increasing from 1/2" to maybe 1".

      We had to get the piping upsized.

      Another consideration with a continuous gas water heater is the range of flow over which the heater will operate. Some of the older models will only heat the water when the flow is at maximum so if you just have a trickle flowing to wash your hands in a sink, the heating shuts off. Most of the later models are very much better and will heat water at both high and low flow rates.

      Check the minimum operating flow rate.

      One other consideration (if you're wanting to spend $$$) is a pre-heater. Basically it creates a loop that allows you to have the hot water circulate through your piping - you hit a button on the controller, it starts up and gets the water in the pipes up to the desired temperature, then you turn the tap on.

      This is instead of turning the tap on and wasting all that water until the system is up and running and the water coming out of the tap is at the desired temperature.

      I'm sure someone here has/will run the numbers of $ on the system vs $ on the wasted water, but it's more than just $ to me (not that I've spent the $ on a pre-heater yet)

      Another consideration with instantaneous is electrical - unlike a storage system with a pilot, a instantaneous system uses electricity to ignite the gas. So you'll use less gas, but if you lose power you lose hot water (unlike a storage system with a pilot)

      • Thanks for this info =I'll also look into the pre-heater.

  • Yes. In our case we replaced electric hot water storage heaters, so there was some generous rebates from the government. Even so, it was quite an involved process.

    Reason being: our hot water line is 10+m away from the meter, so the line had to be upgraded to 32mm to handle the high flow rate needed. 32mm is much more expensive than the standard 3/4" thats normally installed, both to buy and to install.

    I've been very happy with the unit, but if I had my time again, I would probably go with a second hand tank, and a lower spec instantaneous heater. That way the pipework doesn't need to be upgraded. But thats me. I tend to look for inventive solutions to problems, but inventive solutions have a tendency to break more often, so its not for everyone.

    • So you can just install an instantaneous one along with the existing tank?

      • +1

        yep. Instantaneous gas heaters work along a 'temperature differential', ie they take the cold water in, and burn gas until it becomes the temperature you want. The bigger the temperature differential, the bigger the gas pipe needed, and the more stress placed on the unit. By having a tank to preheat the water, you can lower the temperature differential, and get away with a smaller pipe. It won't allow you to use water indefinitely like a proper setup would, but it can extend what I'm guessing is a 150L tank by twice as much.

        But thats a bridge you only need to cross when you need to. Start my measuring the distance from your gas meter to your hot water service. That will give you an idea of cost (because a new gas pipe can double a quote)

      • +2

        I would suggest discarding the existing tank.
        They generally rely on sacrificial anodes to prevent them corroding, and they are sized for ten years approx.
        Our old gas heater lasted 18 years, and then developed a pinhole leak that I didn't spot for two months (I was on holiday in UK for most of that). It was from the bottom of the tank so it wasn't very hot water that was leaking out, but the increased bills for water and gas over that period cost maybe $500.
        You can (in principle) replace the anodes which should give you longer life, but I don't know if anybody ever does.

  • +2

    Yes, best decision ever to go to a continuous hot water system. Cost me about $1800 installed including removal of old water tank.

    • Thanks :)

    • Did you need to get your gas pipes replaced/upsized as hinted to above?

  • Is your flame setting set on low? Can you increase?

    Very strange for the tank not to heat up the next morning.

    • No - it's hot. It's just a small tank, so runs out fast.

  • +4

    We changed to continuous gas around 10 years ago. It was a good decision because of the endless hot water requirement. In retrospect I wished I knew to place the unit closest to the shower so there is less cold water start up. Now maybe also consider electric continuous if you have solar. I remember it was around 3k installed. Half of that was installation costs.

  • +2

    We have had Rinnai and Bosch. Both performed as expected, but the Bosch was cheaper.

    • Much cheaper?

      • +2

        I say -ish because they don't have exactly matching capacities. From memory, they were 16L/min and 18/L min at one price point and 24L/min and 26L/min at the next level. I think the Bosch was about $250 cheaper than the each price point, with the Rinnai delivering the slightly higher performance.
        The 24L Bosch was about the same price as the 18L Rinnai.

  • +1

    Get more than one quote.

    Instantaneous gas units use more gas than storage units so you may need larger gas pipes.

    Consider what size unit you want and you may need to add a power point for the electronics if you don’t have one close by.

    Some people seem to have trouble with instantaneous units cutting in and out with low flow shower heads. If this is a problem the trick is to use the temperature controller (we set ours to 43) so you don’t need to use much cold water. This maximises flow through the HWS so the unit stays on while you’re showering.

    If you rely on really hot water in the kitchen for dishwashing you may need a higher temperature unit with a tempering valve for the bathrooms.

    • Thanks - will do, re quotes. Our last house had continuous as we had installed when we built. Was still running perfectly when we sold it 19 years later.

      There's definitely no low flow shower heads at this house. Judging by the existing shower heads, the age of the dishwasher (which died recently and had to be replaced) and other things around the house, I think the current hot water system would be the original and might well be on its last legs.

      I don't really use very hot water in the kitchen, so I don't think that would be an issue. Our last one was limited to 50 degrees and I didn't have any dramas with it.

  • Our gas storage system has two settings - heat and volume. You may have the same and just need to adjust them. Worth checking before you pay for an upgrade.

    BTW you will find these dials behind the panel where you would light the pilot.

    • Oh - thanks for this. Will check tomorrow.

    • +1

      OP, just because your heater is 14yo doesn’t mean it’s on the way out. You never know how long a hot water heater will last. My Aquamax is 22 years old and has never missed a beat.

      Yes, check the heater controls to make sure it’s on max volume and temp.

      Before thinking of replacing, I’d first install a low volume shower head and encourage shorter showers. It’s also worth remembering that these young folk aren’t going to be living under your roof forever. Your shortage of hot water may be more temporary than you think.

      • Normal steel tanks will last a little longer than the internal sacrificial anodes. Once the anodes expire, corrosion will quickly occur. You can extend the life of some tanks by replacing the anodes.
        You can also get stainless steel tanks which will not corrode. The factors affecting life of these heaters are things like the burners wearing out or the igniters failing - so they may not last any longer than a normal steel tank in spite of the additional cost (maybe $500).
        Having experienced a tank leaking, and needing to get it fixed urgently to get hot water back, I would rather change out a gas water heater at a time that is convenient, and when a gas fitter is offering a good deal.
        You've done well with your Aquamax, and you've definitely had your money's worth out of it! But I would be looking at a replacement for it right now :)

        • Actually, I just checked and it's 23 years old. Yes, having a stainless steel cylinder they don't need a sacrificial anode to prevent corrosion. I've never had it professionally serviced. But I did clean the pilot and main burner about 10 years ago because they kept going out. Being outside, a lot of dust and crap finds its way in.

          I also surrounded the pilot with a cardboard baffle because if there was a really strong wind the pilot would blow out. The other thing I do is open the lever on the PTR valve 2-3 times a year.

          The stainless steel tank came with a 10-year warranty and everything else was only covered for 12 months. Maybe I've been lucky, but Melb water is pretty clean, and I have the temp on a low setting so you can't scold yourself. So its not running gangbusters with a lot of pressure inside the tank.

          But you're right, going without hot water for up to a week when the tank blows is not much fun until a new heater is installed. But I think we'll wing it :-)

  • +1

    The bigger number on the instantaneous the better, don’t cheap out, they get a bad reputation sometimes because people put in the smaller ones like the 16 and it doesn’t have enough for 2 taps at once. Better off with a 26 or a 32.
    Modern taps are often limited to 9lt/minute. Which doesn’t go into 16 twice, which will have people yelling from the shower when you open the kitchen sink tap.

  • Hope you make them pay some of it

    • They do chip in with everything else :)

  • +2

    I replaced gas storage with a rinnai infinity some years ago. It was a bit dearer than replacing with another gas storage system but it is still going strong and of course we never run out of hot water. You use less gas as well as it only comes on when you need hot water whereas storage systems are switching on / off all the time as the stored water will drop in temperature and the system will reheat it to bring it to the required temperature.

  • +2

    I replaced an Aquamax 2000 with a instant gas unit. I also dumped mains gas and went to LPG as my gas usage was so low that my bill was mostly connection fee and it was irritating me. I wouldn't suggest you go LPG because of the number of people who're using the system. I spend less on gas now using Bunnings BBQ gas than I used to on my connection fee, even in winter.

    I just bought a unit from ebay and installed it myself. It isn't complex. I also took the opportunity to relocate it much much closer to the shower. It was perhaps 10 meters of pipe from the HWS to the shower head previously, now it's perhaps 3. Hot water appears much more quickly at the tap now!

    I also mess around with the settings far more than I used to with the old one. As mentioned above, there are 2 settings and they determine the heat that the units create - basically, if you have the gas on high and set the "transit time" of the water through the unit to long, you'll get blister-creating hot water. I find I adjust these as the cold of winter kicks in and I have to overcome the cold in the pipes, colder mains water and so on.

    I run my temperature so that I can shower without turning on the cold at all most of the time. The reason is that (a) it doesn't make much sense to me to heat water past where you want to use it, only to dilute it back to where it's comfortable; just don't overheat it in the first instance and, (b) I have a low flow showerhead so, as someone mentioned, the HWS sometimes gets confused and shuts itself off mid-shower. By not using cold that seems to happen less. Full disclosure though, it does still happen. Ijust say bad words, turn off the water, wait one second then turn it on again.

    So, in my experience, there's minor niggles but it's been well worth it. Changeover costs was I'd estimate under $300. It was perhaps 3 years ago now, so I'm a bit fuzzy on the hard numbers. If you're interested, let me know and I'll see if I can dig up my invoice in my ebay history. Would I do it again? Yes, without hesitation. My last system (the Aquamax) cost close to $2,500 installed because there were "complications", lasted maybe 12 years and just wasn't efficient. If I replace this every 5 years (and I don't think I'll need to) I'll get 25 years of how water for the price of the Aquamax. With much lower running costs (for me; I don't have half of a footy team living @ my place though…) it's all win for me.

  • +3

    Just purchased a Rinnai B26 from for $775 delivered to Adelaide. Replacement for an 8 year old Chromagen instant HWS which has died and has never performed well. The plumber quoted $200 to install the Rinnai so for less than $1,000 total I get the best brand on the market with the best warranty. Winning!

    • Would you mind sharing your plumber details? Am on Adelaide too and Gas works quoted me 410 for installation and disposal. Additional 330 for a PowerPoint.

  • +1

    Where is the location? Here in Queensland the most efficient hot water systems are heat pump models drawing power from solar panels. We switched from gas because our passing charges we more than our gas bill also. We chose a highly respected German unit, 330 litres of tank and it is on a sunshine hours only timer. Plenty of water for at least eight showering one or two times a day. Instal was a doddle, we just put the tank beside the existing gas instaheat unit so we could use existing power and plumbing. It runs on 240 standard power outlet. Water consumption is less because it draws hot water immediately. There has not been any discernible increase in power consumption either.

    Unit and instal was $3,200. Payback will only be 3.5 years at current gas and power prices.

    • Would you be able to share the details of your plumber and the unit with me? I am in Brisbane. Many thanks.

  • +1

    Kmwa has the answers above, my mother's recent experience was $1500 for continuous rennai system + installation + remove old tank, including installing some thermoregulatory thing which is mandatory (and you probably don't have as yours is an old gas water heater).

    Check spec sheets to see how much flow you need at one time, E.g. 2 showers plus sink plus dishwasher?

    Bunnings have cheap units, installation fee is pretty standard, she went with a plumber that quoted she same as Bunnings.

    • +2

      including installing some thermoregulatory thing which is mandatory

      Tempering valve, because we live in a nanny state.

      • +1

        That's the one. Now my hot water can burn me more slowly, and I can use the kettle if I need to soak oven trays. Smfh.

  • +1

    Replaced an electric hot water system years ago. Wasn't ridiculously priced considering that it has outlasted every single prior electric heater.

    Continuous hot water yes, instant hot water no. The biggest downside of these heaters is that they take a while to produce hot water.

    That being said, they will produce as much hot water as you like, whenever you like, for as long as you like. To me, that was a no-brainer.

    • +2

      Unless the gas plant blows up again like it did in '98. Three weeks of fricking cold showers.

      • -1

        And I thought I knew how to hold a grudge.

        • :)
          I use the Longford Gas Plant explosion as a case study for my students in Subsea Technology.
          BHP couldn’t get approval for their offshore Minerva gas development, they kept getting pushed back by the environmental lobby, as it was located in the Port Campbell National Park.
          Then two things changed:

          • Longford blew up and the gas supply stopped, and the general public realised that they actually needed the products of the dirty oil and gas industry.
          • BHP went with a totally subsea development for the Minerva gas field, so there was no gas platform visible from shore, and they even located the Minerva gas plant 4 kilometres inland, so nothing was visible from the coastal path.

          Good that some people still remember this.
          But the kids who are wagging school to protest about climate change have never experienced a gas shortage, and the ecowarriors who are sitting down right now in Brisbane CBD are concerned about the planet but are patently not concerned about us.

          • @kmwa: One of the biggest issues we have as a species is that we don't realise that "us" and "the planet" are the same thing (at least until we have developed suave dating technology anyway).

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