Instant Tank-Less Water Heaters

Hello All

I am looking to install an instant water heater since the traditional gas heater (water storage) consumes too much energy. I feel the gas charges are way too high for my minimal hot water usage with occasional cooking.

Whilst researching on continuous flow water heaters, I came across a few instant electric water heaters. Has anyone here used them before? How do you compare them with continuous flow heaters? BTW, does continuous flow heater really help in reducing the gas bill?

Below are some links for the heaters I looked at:

Instant electric water heater:

Continuous flow water heaters:

Thanks in Advance!

Edit: Thank you all for your kind suggestions. Appreciate it.


  • Check out the heat pump hot water systems.

    If the install is in the right place you can use the exhaust to cool your house in summer.

  • I'd go for something like the Rinnai B26 (get the B series, they're essentially the same unit (capability and quality)) as the infinity units but targeted at builders rather than direct consumers.

    Or a smaller B model Rinnai if you want less LPM.

    You can get them from eBay at a good price, I've purchased on from there before (local aussie stock).

  • We have continuous gas.
    They have an operating life of around 10 years.
    I don't think they are lower energy cost than a storage system that is sized for your needs (I guess if you use little hot water they might be better than a high capacity storage system).
    I would be skeptical of instantaneous electric hot water - it is hard to push enough energy from electricity into the water without having a high capacity dedicated circuit. If you have ever travelled in the UK or Europe where instantaneous showers are wired into a standard 10a socket you will know they are low pressure and tepid.
    Maybe this is different with a whole-house system, but I would want it to be rated at over 20L/m throughput.

    The ebay link will disappoint, I am sure (and note it is LPG). The gas ones linked from Bunnings are ok if you match the flow to your needs. We have a 26L unit that handles a hot, full pressure shower well. The sales materials suggest it can do more than this, but you notice if somebody is filling the sink with hot when you are in the shower. For that reason, I wouldn't choose a 17L or 20L model unless everyone in your family likes warm showers, rather than steamy.

    If you already have gas for other appliances, go for it. If it is just gas for hot water, skip the supply charge and don't bother with gas, and get an electric storage system (and solar panels if that is an option).

    In terms of running costs, the cheapest option is electric fed by solar panels, so you heat the water during the day. If solar is not an option, there are electric heat pumps that are cheap to run (but more costly up front, and perhaps more likely to have faults as there is much more complexity).
    After that, probably off-peak electric with gas close behind.
    Electric of any sort where you must pay normal kWh charges would be the highest to run.

    My long term plan is to replace our gas heating with R/C AC and electric hot water, plus add some more solar panels. If I can convince others to dump the gas cooktop, we will save the $300 a year supply charge too.

    • dump the gas cooktop

      Induction cook tops.

      • Yeah, this is where the discussion is at. Unfortunately, we have never used them ourselves - though acquaintances say they are the goods.

        • We had an induction cook top after I had used gas my whole life and I was fine with it, much better than standard electric. We then went back to gas when we moved house and I have to say, I really miss the induction cook top The fine level of control can't be replicated with gas, much easier for simmering/low heat cooking.

          The wok burner would be the only thing keeping me with gas as I use it all the time. But we'll move to induction whenever our stove dies.

      • Eh, I like my gas cook top, they're dirt cheap to run and there's something in being able to see the flame, gauge the temperature etc - I just never got that same feeling of control with induction.

        My opinion is likely swayed due to growing up with and learning to cook with gas - and a life of cooking on gas.

        I've used induction cooktops about 20 times throughout my life - never felt they could replace my gas.

        Not to mention, using a wok on a big arse 60MJ gas burner - some things can't be replicated easily! (that's obviously not typical gas use, but you got me started!!!!)

  • Thanks for the detailed response - I have altered the eBay link now and there are few sellers on gumtree too -

    • 30amp is certainly a meaty amount of power. Not sure how you could power it without a wiring upgrade if it needs to be in the bathroom, the usual circuit won't handle it. Of course, upgrading the wiring might be pretty straight forward if there is capacity in your meterbox.

  • I second @iDroid's comment about the Rinnai units. A family member is in the plumbing business and recommended a Rinnai when we were building our current place 20 years ago. It's still going.

  • you better be prepared to have your house wired up to scratch to deal with it, the amount of energy such system requires is insane, higher than any normal household appliance, probably tie up with Tesla supercharge station. I think stibel has them, but don't look at the single phase one if you live in the southern state. To give you perspective, incoming water this time of the year is around 15 degree, you'll need to raise it 20 degree (and you'll have to close the cold water tap) to have warm enough water to shower, assuming shower head rate is around 9l/min that translate to 75600 joules or 0.21kwh, or 12kwh in an hour, so you need to wire up 2 of those ebay cheapie.

    Those simple single phase continuous flow type only works for those living in warmer climate, I've seen them in southeast asia.

    • I assume you're referring to instant electric. That'll be efficient only when Rossi's e-cat is less smoke and mirrors and more a consumable we can buy!

  • From my research it looks like if you're a household of 1 or even 2 who take brief showers, it's possible for it to be worth using an instant electric heater if you can disconnect the gas and avoid the supply charge as a result. The more hot water you use the more gas starts to be cheaper as per unit of energy it's just cheaper than electricity. It depends somewhat how you're paying for electricity (eg in SA it's probably very hard to make instant electric worth it). To get the water hot enough most I saw required 3 phase, the single phase / cheap models tended to be quite low flow / for sinks etc.

    If you have solar power and a decent smart inverter etc you're likely better off with electric / heat pump storage and just dumping your excess power into hot water heating unless you're on one of the old feed in tariffs.

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