Hot Water


A response to a post I wrote about things to do for the environment suggested that there would be a health risk to lowering the temperature of a home hot-water system to save power.

I have just been reading about so-called tankless hot-water systems. The concept is that instead of keeping a tank of water hot (which means that you lose some energy due to the insulation not being perfect) you heat water when you need it. The down-side to this is that you need a moderate amount of power to heat water as rapidly as it’s used. The products use between 11KW and 27KW of electricity. The early implementations of this idea used gas – the occasional carbon-monoxide problem with gas appliances makes me inclined to avoid them so it’s good that there’s an electric option.

One of the benefits of the tankless system is that it runs the water at a lower temperature than a regular hot water system. For a tank storing hot water you have to run it at a temperature that kills bacteria (or at least dramatically inhibits their growth) – which means greater than 50C, but for on-demand water it’s safer to have it run at something close to the desired temperature (probably not much above 40C) and not use the cold tap. Lower temperature water avoids the risk of scalding for children and the elderly and if the “hot tap” is running at a good temperature for a shower then you can just turn it on, wait 30 seconds for the pipes to warm up, and jump in! Incidentally it really sucks the way most showers have the taps under or behind the flow of water, so if the water becomes too hot before you get in then you end up getting minor burns in the process of turning on the cold tap.

I still think that solar hot water is the way to go. It apparently combines something like a tankless system on water that comes out of a tank heated by the sun. So during winter it operates like a tankless system but in summer you get more hot water than you can use.

This web site about Solar hot water systems indicates that they have a similar technology to “boost” solar hot water, so if the Sun doesn’t make the water hot enough then it can use electric or gas systems to further heat the water. It’s also interesting to note that they offer Heat Pump hot-water systems, it’s a pity that they apparently don’t support combining this with solar heating. Another interesting feature is what they call the Water Guardian that pumps cold water from the pipes back into the water tank and avoids wasting the water that you might otherwise run down the sink while waiting for it to get hot.

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16 thoughts on “Hot Water”

  1. Pingback: Gunnar Wolf
  2. VE says:

    pleeeeease… you want to do things “for the environment” and you advertise electricity to heat up water?

    Thanks Gunnar for telling him.

    We’ve also had gas heaters “on demand” in Italy for ages too…

  3. Jo Shields says:

    Is this an uncommon scenario in the US? Most new installations in the UK these days use either gas-based condensing combination boilers without any tank behind them (or a couple of litres at most in high-end models), with a variety of vendors offering their wares, e.g. or electric immersion tank heaters (the rather more expensive option)

    The downside to a combi boiler is the maximum flow rate may be lower than you could get from a tank, which sucks for taking showers (well, it does when you have a crappy boiler like mine anyway), but it’s nice to have water at the desired temperature within a couple of seconds without needing a tank

  4. Thomas says:

    In Germany, they actually have a lot of flow water heaters. Personally, I wouldn’t want to miss them. If your floor-plan allows it, you can use one device for kitchen and shower. Also, in my experience, the gas-based ones are very safe as well as long as one observes the regular maintenance (usually done yearly, costs about 20 Euro or something like it).

    At an energy efficiency of 99% (, sorry, German), if you’re able to produce energy with high efficiency, you’ll have instant fresh (for cooking) warm water with very good energy usage.

  5. etbe says:

    VE: Electricity can be generated by wind and solar power. Gas always produces climate-changing CO2.

  6. VE says:

    Russel: you get the point, in fact you say that electricity “can be” generated by wind and solar power.

    Also, be careful with the wind and solar and CO2: wind mills are made from steel that’s produced with a hugely unfavourable CO2 balance. Ever wondered why the steel industry is such an active sponsor of wind farms?

    But until sun-wind becomes a reality (and I’m sure it will) you shouldn’t be urging other people to buy an american electrical appliance to heat up water suggesting that it is “for the environment”… I think

  7. Adam Shand says:

    Tankless hotwater systems are moderately common in New Zealand, and I love them for all the reasons mentioned above.

    However, I was recently at a conference and was extolling their virtues when an engineer who works on the national power grid stopped me and said that actually they are a huge problem from an energy (electricity or gas) provisioning point of view.

    His argument was that because …

    * most hot water is used in fairly narrow bands during the day (morning showers, evening showers and clean up)
    * the *throughput* of energy required by a tankless system to make hot water on demand is huge (compared to the requirements for keeping a tank hot)

    … tankless systems would cause widespread issues with the gas and electricity delivery systems if the majority of the houses used them.

    Which is a shame, because I *love* them :-(

  8. craig says:

    continuous hot water systems have been around for years. i’ve had gas ones in the last few houses i’ve lived in (at least all of the last 15-20 years). they’re great. much cheaper to run than tank systems, they use energy only on demand, and they NEVER run out of hot water, no matter how many mooching sponges you have crashing in your house on any given weekend.

    i’d never have a tank hot water system again.

    our current unit provides hot water for both bathroom and kitchen.

    carbon monoxide poisoning is not an issue, either. indoor units have a flue taking exhaust gases out through the roof, or they can be mounted on an external wall of the house (e.g. bathroom)

  9. etbe says:

    VE: Steel can be recycled and wind farms will last for a long time with little requirement for new steel in the maintenance. Wind power is rapidly being adopted in most countries, and in Australia it is possible to pay a little extra to get “green electricity”.

    Adam: That’s a really good point. However if you have a disconnected solar PV system on your home then the batteries will be able to supply that power with ease. Also there is talk of using a Prius (or similar car) as a home battery. The battery in a new Prius could handle two of the tankless hot water systems at the same time!

    Craig: CO poisoning should not be an issue, but there was a report on the Australian TV news a few years ago of a woman dying while having a shower from a hot-water system (presumably tankless if it turned on when she had a shower).

  10. VE says:

    Russell: this may surprise you but I presently work for the tenth steel maker worldwide (in order of Mt/year of steel produced). It s true that steel is highly recyclable. This is done by remelting the scrap steel it in Electric Arc Furnaces (EAF). One medium sizes EAF has a yearly electricity demand comparable to that of a 300k households. It’s one of least energy-efficient industry.
    Steelmakers push on windfarms like chemical companies push on solar cells: believe me, it’s all about big money. When talking about the energy content of any object, we should only use a cradle_to_grave approach (scientist call it Life_Cycle_Assessment).

    I don’t know the way Australia is dealing with windfarms, I’ll tell you what happens in the EU: huge public money is contributed to build the windfarms to clever guys who go to small city councils in the middle of nowhere and convince them it is “for the environment”. There’s never a scientific assessment if the yearly average wind speed justifies the investment. You’ll find wind mills in the least windy places. Crazy.

    One good thing we can do “for the environment” is promote a policy of “sustainable decrease”. In the case of hot-water, we should decrease in a smart and thinkful manner our level of consumption of hot water irrespective of the way we heat it. And this reasoning should apply to whatever we consume.

    Hot water example: in Italy (my country) every household will boil about 3 litres of water for 15 minutes twice a day using methane as fuel for cooking pasta. Bloody heck, you just need to bring the water to the boil, throw the pasta in and SHUT OFF THE GAS and pasta will cook at the exact same way without boiling till the end. We’re not smart, we’re not thinkful and we consume more hot water than we actually need…

  11. Adam Shand says:

    VE: Can you cook dried pasta like that or only fresh pasta? I didn’t realize that will work, I’ll give it a try next time!

  12. VE says:

    Adam: for dry pasta requiring let’s say 13 minutes you just boil for the first minute and then you let it sit unstirred for the remaining time or until it is soft to your liking.
    A little less CO2 is emitted.

    But don’t get me wrong, citizens can do a lot for reducing CO2 emissions and mitigating climate change, but the results will only be visible when the big industry will change their attitude (oil companies, power generation, automotive industry).

    It’s too easy to blame households to over-boil pasta or over-illuminate their rooms, isn’t it?

  13. Adam Shand says:

    VE: Absolutely, but when there are things that it’s easy for you or I to do, I like to know about them and do them. Being able to do little things is often a way to combat the helplessness that some people feel in the face of the problem.

  14. Eduardo says:

    The “” do they have a distributer in Australia?
    Is there more brands of tankless system in Australia?

    Kind regards

    Eduardo. Tirado

  15. etbe says:

    Eduardo: I’m not aware of a distributer in Australia, maybe if you send them an email they will be able to point you to one.

    But Adam Shand’s comments make me believe that solar hot water is the best option if you have roof space for it.

  16. etbe says:

    Comments about this topic (or any other) that merely advertise products or services will be deleted without anyone reading them.

    If you make an informative comment that also happens to include a single URL about the services your company offers then it has a good chance of being approved.

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