Need a New Hot Water System - Things to Ask / Recommendations?

Hi all - we need to get a new hot water system (30 year old low pressure roof cylinder leaking).

We are in the process of getting a few quotes for like-for-like, upgrade to mains, and potentially a gas system (we have gas to the property).

Has anyone replaced their system recently and have any tips? What should I be looking at RE upfront vs running costs, efficiency, etc?



  • +1 vote

    I haven't replaced a system recently, but we moved to a place without a hot water tank - just the instant heat gas system, and it would be very difficult to go back to an old tank system, especially with kids / teenagers in the house.

    It is now impossible for them to run through the hot water!



      And I have the opposite opinion - I thought I'd left those dreadful things behind when I moved back here from the UK but I'm now in a rental that has gas hot water and I hate it. Then again I live alone and not likely to deplete a hot water cylinder capacity so I understand it's different with kids.

      The problem I find with them is there's a minimum flow rate needed for the gas heater to kick in - so you can't run just a small trickle of hot/warm water, it just comes out cold if there's not enough to trigger the system. I feel I'm wasting water a lot of the time because I'd like to use a lesser flow rate but I can't. Rinsing the soap off my dishes as I wash them is a particular problem because I never run enough to trigger it which means I end up with cold water coming through which makes the dishes harder to dry. Or I run it long enough to heat up again but then the hot water in my sink gets cold in the process.

      And the other problem is the shower temperature fluctuates up and down. After a while it can go lukewarm for about 20 seconds until the system 'catches up' somehow, and if you dare use the mixer tap to try to increase the temperature when this happens then it 'catches up' to a scalding temperature.

      At least I have hot water. I shouldn't complain. I just thought it was one of those UK things that I'd gladly left behind.

      All that said when a family member was looking into a new hot water system, the little research I did for them indicated a gas system could be more economical over time (I didn't realise they needed semi-regular replacing) but only if you had gas to the house already. With gas bottle deliveries which another family members holiday house used, it was going to be more expensive than regular hot water cylinder.


    Check out this government funded tool for comparing water heating systems:

    There are basically 3 types of water heating solutions in NZ, electric hot water cylinders, gas powered continuous flow heat exchangers and heat pump water heaters; depending on where you live, the last one is probably not an option unless you are in the upper North Island.
    My research is that the cost of running electric or continuous gas is basically the same, especially if the gas is direct to your property although this can depend on the cost of the power source; the main difference is the up front cost, maintenance and longevity of the system. I am not familiar with the cost of electric cylinders installations however these must be installed internally and it may not be fit where the previous one was. If you can reuse the same location and plumbing this may be the best bet.

    For gas, the upfront cost is usually is roughly about $2000-3000 for the external unit, the internal controller, piping and installation by a certified gas fitter, depending if you have the infrastructure already set up (such as you already have gas for cooking). I've found that the external unit requires replacing every 10 years or so depending on the harshness of the water, if you're lucky your house insurance will cover the replacement after it blows up. In NZ there are 2 basic brands of heat exchangers: Rheem and Rinnai. I have found Rheem to he cheaper overall and the quality about the same, however the fitting placements are different for each brand and therefore it difficult to change after the piping has been installed.

    As usual, shop around with the installers and pit them against each other, some dealers as the Cylinder Guys wanted about twice the amount to replace the same unit as another small independent certified installers so it can vary wildly.

    • +1 vote

      Hi, thanks so much for your detailed reply.

      We are Wellington-based - I assume a heat pump option is therefore less attractive?

      Our ceiling access is small, and the current system is low pressure - we would likely need to get the access widened, and replace all the valves etc, according to a quote we've had so far.

      We do already have gas for cooking, so this is an option I am leaning towards. I didn't know the units needed replacing though, we are near the coast so it's possible this might be even more frequent (salt air etc).

      We have asked around half a dozen places for quotes. Definitely interested in both up-front costs as well as ongoing running costs.

      We have solar PV panels and are keen to try get a system that has a timer or similar to help us make the best use of those.

      Appreciate your advice - if you know of any good contractors in the Wellington region, keen to get a recommendation.


        Wellington might be a little too cold for the heat pump to effectively heat up the water to the minimum safe temp throughout the winter, probably would not advise this route.

        Sounds like it will be more effort to have a electric cylinder installed in the same location. You could perhaps sacrifice some cupboard space instead? The benefit of electric is you could use the electricity from the solar investment to heat it; however this may not matter that much if you are using more or equal to the amount of electricity generated as that will mean you're buying from the grid anyway.

        Not too sure on what you mean by timers etc. however frequently turning off electric hot water cylinders is not advisable due to the increase in risk of nasties brewing up inside it as well as it costs 4x the energy to reheat the water up to the same temp after it has cooled off; in most cases it is safer and cheaper to maintain 60C water rather than letting it cool off and reheating it.

        If you already have gas for cooking, it is probably easier to route this supply to an external location, install the gas water heater alongside a standard power outlet (preferably external) and then route the hot water back into the house.

        I do not believe that salty air makes that much of a difference externally to gas pipes as they are either galvanized or lead (yay for lead pipes!); corrosion from the outside will take a long time, however if your water is harsh (or salty) that may affect the life of the heat exchanger. Usually the exchanger is located above the electronics in the unit so when it starts leaking it fries the electronics as it drips down (however replacing just the heat exchanger is basically the same price as replacing the whole unit so it doesn't actually matter as much).

        Don't know of any contractors in Welly but I'm sure your Cheapies senses are on point anyway :)


        Hey, we are in Wellington as well. Keen to know what you go with.

        Our initial thought was continuous gas since its piped to the house and have 2 bathrooms. Also on low pressure at the moment so really looking forward to mains pressure.

        From research gas running cost is similar to electric since daily charge but having the unit outside will mean we get extra space in our laundry and hopefully more interest from family buyers.

        Online some installers mention about cleaning internals of continuous gas systems with vinegar solution.

        If you can please tell me who you use and your experience / cost. Also any tips you came across when buying.



          Hi - we've decided to go with gas infinity, through an offer from Nova energy:

          This pretty much covers the cost of a standard install (though we are paying a bit more due to additional piping and a controller) and you pay it off over three years on your power bill.

          Our house already has gas which makes it a good option for us. Our next best was an outdoor cylinder but those are bulky and not especially attractive. Similar costs upfront though.

          I haven't seen anything about cleaning the gas system but it does apparently need to be serviced every couple of years (though supposedly cylinders also need to be serviced).

          My main advice is to get a bunch of quotes - lots of people mentioned different options and prices so it was helpful to hear several opinions. Some think gas can be noisy, some think electric outdoor is less efficient, some think upgrading to main is good but others say stay with low as additional cost to upgrade. Every house will be different!

          Good luck :-) let us know what you end up going with!


            @joshtnz: Hi josh, how are you getting on with this deal?
            They have extended the offer but I noticed you have to stay with them for 3 years and their rates are higher.
            Do you find that your monthly bills offset getting this installed directly by plumber?



              @Foodie: Hi, this offer ended up being nearly $1000 cheaper than the nearest offer we could get from a plumber for the same kit. Paying it off over 3 years means we didn't need to put it on mortgage or credit card, and have money free to play with in the meantime. Their gas rates were already really good for us though electricity is a little higher than the previous provider. I guess it depends on your circumstances but I've found this to be a really good option.


                @joshtnz: Thanks for the info. I have them coming out tomorrow to look at installation.
                I got some estimates of $3500-$4500 for the install from plumbers so have the same experience with you there.

                They are giving me $150 to sign-up and can save on my current price of power slightly. Currently our power is mainly on hot water with our old cylinder likely having some impact due to it's age.
                Of course keeping in mind the additional daily gas charge I'm hoping it averages out.

                Also I asked that if we choose to leave after a year we would just have to pay the remaining total of the system. So there is an out for it.


                  @Foodie: The install prices are interesting - I just had a look and the tradie price for a Rheem 27l unit is around $900, if hot water pipes are within 5 metres then that's less than $100 in pipes and fittings. Depending on where power is, that's another $100-$300. Then there is the gas regulators, etc, if you hire the bottles then there is no upfront there, only a $10 a month rental + $100 fill charge. Worst case scenario that is $1500 without plumbers labour which should only be about 4 hours @ $80 or so an hour = $320.

                  I suppose it all depends on how difficult the install is.


                    @Toddy47: Add on additional travel to job costs and taking on liability if you have to come out to resolve some issues arise. Removal of rubbish and old cylinder, temperature control panel and what ever padding they add to their costs.
                    It all quickly adds up but I agree, for purely the cost of supply and fitting with nothing else then it will always come out cheaper.

                    I've been quoted $700 to install (not supply) a dishwasher and hook up tap (not supply) in a new kitchen.
                    I guess there is an issue as a consumer that if places are busy enough they can quote whatever they want as they are not desperate for work.


    buy A Rheem Califont from a plumbing shop most of these plumbing shops give people a 15% discount pretty easy. then hire a gas fitter to install it. If you just pay the gas fitter to buy it for you, you will not get any discount. You could save a few dollars by doing that.

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