Last week, I extolled the virtues of heat pumps, lauding their unparalleled efficiency. As promised, it’s time to investigate why these newfangled appliances might not be as splendid as they seem.
Strap in as I let off some steam about why using refrigeration technology to heat water just goes against the natural order of things.
Woke Water Heaters?
Before we dive deep, let’s clear the air. Some commenters reckon heat pumps are a ‘woke’ fad. I’m not here to politicise physics. The heat pump hot water hype train is chugging along full steam here in Australia, and it’s true they’ll play a big part in our move to electrification. But we need to consider a few curly issues before chucking these things in every backyard.
The Appeal of Simplicity in Resistive Hot Water
A standard resistive electric unit is a model of simplicity, embodying the KISS principle. Its minimalism is its strength—two key components, an element and a thermostat, constitute the entirety of its makeup. Both are inexpensive, readily available, and understood by electricians and plumbers alike.
Contrast this with the more complex structure of a refrigerative electric hot water service. This contraption boasts two motors—for the compressor and fan—high-pressure refrigerant, multiple components (pipe joins, welds, condenser, evaporator, TX valve, filter, drier, pressure switches), and a layer of sophisticated electronics. These include temperature sensors, programmable timers, and even external solar controls for enhanced self-sufficiency. The multitude of components adds weight and introduces many potential points of failure.
Instant gas-boosted heat pump. i.e. two complex machines in series. It’s a cheap install of cheap gear. There’s little to like here.
The Service Conundrum: Who to Call?
Heat pumps aspire to the reliability of fridges. But the increasing complexity and sophistication of heat pumps can lead to serious maintenance issues. When a heat pump malfunctions and customers complain about cold showers, they often consider it a bona fide emergency. Who do you send to fix it ASAP?
A triple threat tradie skilled in plumbing, electricity, and fridge mechanics is a scarce find. So imagine the operational headache of urgently dispatching three separate vans for three appointments just to diagnose the problem. Additional visits may be needed if special parts have to be ordered. Contrast this with the simplicity of dealing with a resistive unit where every decent plumber or electrician carries a thermostat and element—universal parts that make repairs cheap, fast, and simple.
An inexperienced plumber totally screwed this refrigerant connection up, twisting the pipe until it was crimped shut. I unwound it, and how it holds gas continues to amaze me.
Dissecting Warranty Claims
It’s crucial to scrutinise heat pump warranties carefully. While some brands boast about a 10-year warranty, the fine print often reveals a different story—major components may only have five or even two years of coverage. This can lead to unexpected costs if your unit fails and can’t be repaired.
Poor People Pay Twice
Free heat pumps are bloody expensive.
Many people fall prey to the allure of subsidised water heaters offered for “free” or at a significantly reduced price, especially when deciding under the duress of cold showers.
The initial savings can turn sour when the unit fails. Repair costs can exceed the original outlay, and full replacement can run into thousands of dollars—especially as the one-time rebates that made the first unit affordable have already been spent.
“Don’t waste your rebates on junk” Good plumbers are calling out cheap rubbish via social media.
The Dark Side of Heat Pumps
Not all heat pumps are subpar, but some big brands have been known to disappoint.
I have it on good authority from three different plumbers that a large water heater company would advise the plumbers they knew units they were selling were crap but the customers should be kept in the dark because new models were coming with fewer known problems causing warranty failures.
It’s scandalous that some units were sold with known issues, on the assumption that if they were good, they would last for years, but if they were lemons, they’d be scrapped.
This approach has damaged heat pumps’ reputation among customers and tradies. Bad experiences with big-brand heat pumps are a big reason your local plumber often warns you off buying any brand of heat pump.
Noisy Neighbours: The Audible Annoyance of Heat Pumps
Cheap or unmaintained heat pumps create noise, which can lead to disputes in densely populated areas.
As urban density increases and McMansion footprints expand to the plot’s boundaries, machinery like air conditioners are often jammed together in service corridors next to the fence. Not only does this make for noisy living, in some cases a lack of good airflow wrecks the performance of these machines too.
Heat Pumps Are Killing Solar Hot Water
Solar hot water systems, once the pioneers of energy efficiency, are now overshadowed by heat pumps.
Solar thermal hot water used to be celebrated for its ability to work without electricity for much of the year. As heat pumps gain traction, solar thermal units have been brought undone by plumbers who don’t want to run plumbing and crane tanks onto the roof. Also, many project homes are technically unable to carry 500kg in four square metres.
In 2008 I helped install this on a roof the salesman said “wasn’t too steep” and ended up buying the house next door years later. She’s still there at 15 years 4 months, and counting
The things you can do with a crane having 9 metres reach. Image credit: Solar Depot
The other configuration of solar thermal hot water, a split system with a tank on the ground, did away with a roof-mounted tank but introduced a pump, pipes, sensors, wiring & associated unreliability. Many failed and morphed into plain electric hot water relying on the booster element or a downstream instantaneous gas unit. In both cases, they were expensive to run, and people didn’t realise they were actually broken.
For all their faults, solar thermal hot water is still a great way to harvest free energy. My old mate Derek loved home brewing because, on a hot day, he could sterilise bottles with “boiling hot” tap water. And like a heat pump or solar electric system, they still attract STC credits. However, if yours needs repair, the tendency for trades to pick the easiest, and let’s not forget the quickest option, means that heat pumps are often the answer.
Refrigerants Are Often Nasty
If we are moving to efficient heat pumps mainly to reduce energy consumption and atmospheric pollution, then we really need to address the refrigerant used. Propane and CO² are pretty benign, but fluorinated hydrocarbons R134a & R410 have a massive impact. If just 500 grams of R410a escapes, it equates to over a ton of CO² equivalent global warming potential.
The Future of Heat Pumps
As we decarbonise the economy addressing many homes’ largest single energy consumer is essential. As we’ve already noted, Australian rooftop solar is the cheapest electricity ever generated and storing that energy in a hot water tank is much cheaper than chemical storage in a battery. Midday is the new off-peak, and electricity network thinking is being turned on its head as a result.
What worries me is the amount of oil, refrigerants, electronics & other resources we will pour into manufacturing heat pumps. I would be fascinated to hear any hard numbers but considering weight alone, I can see tons of water heaters being smashed out that really should be serviceable, durable, and heirloom quality… but I have a funny feeling they won’t last.
If we are going to install millions of heat pumps, let’s install ones that can be maintained over decades, and have trades that know how to repair instead of scrap them when things inevitably go wrong after many years of daily service.
What’s Next?
While I’ve voiced my concerns about heat pumps, I’m not leaving you in the lurch. Tune in next week when I’ll reveal what I believe is the best solution to the hot water conundrum. Here’s a hint—it’s as timeless as copper.
About Anthony Bennett
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Having been through two heat pumps in 11 years (I won’t name the brand but it is what I believe to be a good quality German one), I went back to resistive on controlled load for a lot of the reasons listed in the article. I’m still having trouble 12 months later for properly disposing of the last heat pump – which is a point that relates to “Who to Call” and “Refrigerants Are Often Nasty”. It costs to get them de-gassed and they are heavy! While I’m sure someone would just take it away (for a price), I’m not sure they would do the right thing!
What is the solution for apartments (and even McMansions), where there is no space allocation for a water tank, to move away from the in-wall gas instantaneous hot water? As these gas units age and fail, some people would love to move away from gas for environmental and health reasons. Gas might also eventually be banned etc.
Have had a heat pump water system in our old house for 15 years without any trouble. Saved at the time compared to an electric water heater about 50% on bills. In a new house, now the German machines, which are now made in Hungary for 4 years with no trouble. Poor instaltion might be the problem with other heat pumps.The Australian version copied from the European ones, plumbers have told me, are a problem.
Great piece as always, thank you. This is what has held me back from hot water heat pumps, even though we use heat pumps for all house heating for example. Too many reliable people telling me they’ve had a nightmare experience with faults and finding knowledgeable repairers and installers.
Unless you buy an ultra cheap heat pump, it will have the old fashioned resistive heating element built in as a backup for high demand and or really cold days.
This also means that this backup works should the heat pump in your water heater fail. Basically there are 2 hot water systems built into the one tank. This makes these systems more reliable in all fault cases other than the electronic controller breaking. Which is a rather unlikely cause of trouble.
Good Article. As I have said on a number of occasions, I like the simplicity of Resistive HWS. Easy to maintain & replacement is cheap. The other advantage is you can have more than one HWS so the pipe runs are really short. (eg one for thew main Bathroom, & 1 for Kitchen/laundry depending on house layout.)
The main thing to remember is if you use a timeswitch, use a battery backed one, & switch the element with a contactor. Also order the HWS with a 2.4Kw element. This means the HWS will be on for longer, but matches the solar o/p better. The PV system would need about 1.5Kw extra to match the load, but if your system is oversize anyway, it would not be an issue.
Another alternative is to use a Heat-tube close connected smaller solar HWS, with inbuilt heat exchanger coil system as a pre-heater feeding small resistive HWS as above. This means the systems are fed by fresh water that is heated by the heat exchanger, so no issues with any nasties growing.
I feel the passive systems are the best options: easy to recycle, relatively cheap. & on the occasional cloudy day the cost of power is not excessive (lets face it, even on an overcast day the PV system still generates something).
Doug, you are spot on as there must be huge amounts of water wasted due to long hot water piping runs in many houses. In our case we found that it took about 10 liters of cold/cool water wasted if we wanted to use hot water in the kitchen. Putting a compact 25-liter resistance heated unit under the sink and a time switch has cut out almost all that wasted water as well as allowing us to have really hot water in the kitchen. I also found that connecting the dishwasher water supply to the new hot water heater meant that we reduced the power needed to run the dishwasher and achieved an even more efficient result as we use most of the water that was heated during the day. It only takes about 1.3kWh to heat 25 liters of water to a useful temperature. The bonus is the small water heater is made in Australia.
1 metre of copper pipe = .14 litres.
I get what you are saying with water wastage, but the environmental cost of a 2nd HWS would be 1000’s of litres. I’m not sure payback would be possible.
Hooray! – you actually mentioned the issue of contained refrigerants! – something we seem to studiously ignore. ALL fluorocarbon refrigerants contained in AC, heat pumps and domestic refrigerators (as well as the big
industrial cooling systems) will eventually be released to the atmosphere
and, as they can contribute see also
https://www.dcceew.gov.au/environment/protection/ozone/rac/global-warming-potential-values-hfc-refrigerants
To see what a future time bomb exists in this world – Google “Airconditioning pictures Asia” – and most of these will use high GW impacting refrigerants such as R22. (oh, and don’t forget automotive AC!).
They will almost all be released to the environment. Great prospect!
One element (pardon the pun) missing from this debate is the idea that the most energy efficient thing to do is to USE LESS HOT WATER!
The best, and most cost-effective thing we can do is to take shorter showers!
Why is it that energy conservation seems to seldom be mentioned in discussions about decarbonising the economy… oh wait, now I remember… because nobody makes any money if we just simply choose to use less.
Andy, short showers are great but some households could also save a huge amount of energy/money by installing low flow shower heads. Most modern ones are around 8-9L/min and older ones can be 15-20L/min. We replaced a 15L/min one and a 9L/min one with two 5L/min low flow shower heads. 12L/min to 5L/min… the maths are compelling.
Even ordinary households with 9L/min shower heads could cut hot water use by 50% with low flow heads.
Guy, I’ve been looking at replacing our 9L/min showerheads with 5L/min ones. Which ones did you purchase, would appreciate the brand or a link to the 5L/min showerheads please. Thank you!
The issue is also parts
We do not have a heat pump water heater but we do have a air condition which replaced the previous branded one because they could not supply a circuit board for less than a new unit.
Note the same issue also applies to gas central heaters where they scavenge the circuit boards out of old units where they can as that is the only ongoing supply
Hi Anthony, i have installed Istore heat pumps at 2 properties over the last 5 years and my experience is very positive with both. Coupled to solar panels they lower water heating costs by 75% and have had no issues whatsoever, would have no problem reccomdending this brand of heatpump.
“Who do you send to fix it ASAP?”
I’d suggest if under warranty, then it should be the system installer. If the system installer/service agent is no longer available or unable to respond, then contact the distributor of the equipment for sourcing possible alternative service agents in the region.
“I would be fascinated to hear any hard numbers but considering weight alone, I can see tons of water heaters being smashed out that really should be serviceable, durable, and heirloom quality… but I have a funny feeling they won’t last.”
Is it any different with any other appliances? Air-cons, TVs, microwaves, computers, etc.?
I’ve observed that the Sanden heat pump system I have is modular.
The water pump, fan and motor, 2 circuit boards, LED display unit are replaceable.
The 250 litre tank is stainless steel – I’d expect it to last decades.
The thermal sensor in the tank is replaceable – mine was replaced under warranty (with a different design sensor assembly) due to water weeping around the electrical cable.
The 2 circuit boards each have a replaceable fuse. In Feb 2023, the fuse on the secondary board ruptured on my unit, and the unit stopped working. The service agent found a dead cockroach below the board, replaced the fuse and sprayed surface insecticide into the internals of the outdoor unit, and the system was back in business.
I’d suggest unless the Sanden HPWH system loses refrigerant or the compressor deteriorates/fails, or the enclosure is extensively damaged, it’s probably possible to keep the heat pump going indefinitely (until replaceable spare parts for that model are no longer available).
In my experience Sanden fully support their product when problems arise during the warranty phase, and after.
If most people continue to perceive HPWH systems are too risky & not cost-effective to adopt, then HPHW systems will likely remain within a niche market only.
Thank you so much for this article. Saw a installer a few weeks ago, I was in the market for an evacuated system as I’ve had one on a previous house. The installer did his utmost to talk me out of this and very quickly got me to sign for a cheaper heatpump, I cancelled the deal the next day as I felt pushed into something I might be sorry about down the track.
Evacuated glass tubes are so effective, a favourite of mine too.
Except when there are hail storms. Saw many broken by hail when serving in the SES.
What a great great article!
Most people these days are putting in bigger solar systems me included and with my resistive system and a catch diverter set on solar only I’ve always got hot hot water for FREE except for the lousy fit I would’ve got!
As someone with an annual income of approx $32K, all this debate about heat pumps is like hearing what series of the new Mercedes is better.
Good luck to you all, but just the cost of a potential repair bill rules me out completely.
I’ve been saving for a replacement for my gas-fired hot water system, but bloody hell the choices are limited.
I’d suggest instead of getting another gas continuous unit & going broke, put your similar amount of money into a medium quality heat pump system such as Apricus or Quantum.
Both propane refrigerant, & vastly cheaper to operate over time than gas.
The subsidies in NSW at least are now very good, with the new ESCs shaving another thousand & more off the purchase price.
I can’t see how people have got this so wrong. Resistive hot water is so easy. With solar panels when the sun shines you can heat water. Off peak is a thing of the past but heating water by resistive is easy during the day. Problem in South Australia is that it is illegal. If you have access to a gas connection you are prohibited from installing anything other than gas or heat pump. We have said ‘F’ you to the rules and installed extra panels which are not grid connected but supply power to a 1.5kw resistive hot water and also to a sand battery for supplemental room heating.
Total cost is way lower than a solar thermal water heater and it works.
Hi Brian, the sand battery concept seems very interesting but I can’t find much on it other than commercial prototypes. Could you please provide more details of your sand battery such as where you bought it from, cost, and how you’ve used it for supplemental room heating?
Mort: – “I’ve been saving for a replacement for my gas-fired hot water system, but bloody hell the choices are limited.”
What life do you expect to achieve for your replacement gas-fired hot water system? I’d suggest (for the eastern & central states/territories of Australia) you may find the gas supply to run it over its expected operating life may become unaffordable in the years to come.
https://www.solarquotes.com.au/blog/heat-pumps-explained/#comment-1580174
Gas demand for power generation & industry both peaked in 2014.
Gas demand in the combined residential and commercial sectors seems to have peaked in 2021.
https://thefifthestate.com.au/columns/spinifex/charting-the-decline-of-the-gas-era/
The resistance electric tank heater would seem to have a future simply because many apartments are unable to install heat pumps (unless there’s a version that works completely indoors I’m not aware of). In fact according to the UTS research team below heating up a couple of million resistance heaters at times of low demand and switching them off during peak could act like reverse batteries that would firm the grid VPP style soaking up our solar surplus and saving a motza in storage, poles and wires.
https://reneweconomy.com.au/electric-water-heaters-could-do-work-of-2-million-home-batteries-and-save-billions/
So seems smart control of electric tank heaters could be a promising aspect of the renewable transition. Of course they aren’t very efficient but can run from renewable sources, so with the right public-private partnership approach grid firming savings and lower upfront costs could lower bills and fund renewable generation and storage.
We recently replaced ours and went with the most efficient stainless steel option, and you can lag the hell out of the piping, but another benefit of using heaters for smart demand smoothing is that that on average 25% of the electricity goes to standby losses. At least some of that would be saved if they were mainly heated in the middle of the day before a few hours before water is used in the evening peak.
Why not run a scheme to replace gas/old electric tank heaters in apartments and put them on a reverse battery VPP like this.
Hell I’d accept the odd cold shower on a hot day if they pay me enough to keep our heater off…
Well reasoned Guy,
Sadly the people who ring up with complaints about cold showers are often pretty irrational about it. If you imagine the stereotypical bored home maker who’s got nothing to do but fret… they’ll give a lot of money to less than scrupulous plumbers to make the problem go away quickly in my experience.
Indeed. If govts can subsidise heat pumps they could also look into the UTS teams idea for apartments. Really joined up government thinking would identify apartment roofs as a key untapped solar resource near to consumption and work up a scheme that allows them to install smart metering and get EV ready while installing solar arrays as part of VPP deals with batteries or resistance heaters on timers. Govt could provide subsidies and interest free loans tailored for this. New renewable generation, plus benefits for grid firming if residents got to use some off peak electricity from their own roof while the rest went to batteries controlled by energy retailers for it to use at peak times.
I hear what you say about cold showers, but the UTS people did mention the water heaters in reverse battery VPPs would best be a bit oversized.
There are aircon/refrigeration companies about, and an aircon in reverse gear, connected to a water tank, ought to be grist for their mill. In principle. Availability of parts for myriad models of spat out consumer grade units will always be a problem … or just an element of planned obsolescence.
For my recently completed rural build, I had pencilled in the “Bolt-On” heat pump module, which could be plumbed to any HWS, and plugged into a GPO. Sadly, the vendor vanished before I could lay my hands on one. It still seems to me to be a fine idea, worthy of effective commercial execution. (I had planned to mount it in the roof space, so that it could cool up there while heating water – very nifty in summer. Sadly that notion will now not be tested.)
So now there’s just a 2.4 kW element in an all-copper HWS with a long heat exchanger coil inside. Additionally a wood heater in-flue jacket heats water circulating through the tank by convection. That’s vented, because of the uncontrolled heat source. The unit can only deliver 11 L/m of hot water, as mains pressure cold water must extract enough tank heat in one pass through the coil. It works fine for one retiree – maybe not so well for a tribe of teenagers.
The idea of loading the roof with a heavy installation that can leak did not appeal, and a SQ article reminding that the roof area can do more than heat water if covered by PV panels, sealed the fate of direct solar water heating.
If the atmosphere can hold 7% more moisture for every additional 1 degC, then there’ll be ever more cloudy weather, already observable in summer, I sense. And (soon?) there’ll be an EV to feed electrons to, if they’ll just make a decent single cab ute.
In 2009 I installed a solar hws with a tank on the ground and used a solar gas instantaneous hot water heater for when solar alone wasn’t enough. I moved in Dec 2009 and in may 2010 noticed my water was not hot enough. After checking the plumbing and electrics around the hws I realised I had not plugged in the gas instantaneous hws. 5 months on pure solar heat free from the sun. Had gas Cooktop and hws only and received bills for $55. Approx $5 gas usage and $50 service to property. And Now gas is the devil. Heat pumps everyone come and get them…One shoe does not fit everyone… I like my water hot not hottish. During winter when very cold,wet and overcast your solar power generation is at its lowest and your heatpump is consuming the most power during that part of the year. In 2009 I received the best solar hws rebate as I originally had electric storage hws. I received the highest $$$ on offer because how bad it was at being energy efficient. And now it’s storage hws to the rescue all powered (mostly) during peak use in winter evenings when there is no sun by the best brown coal money can buy…
Evacuated tube hot water is great in summer, when the temperature is good. We had a big job when the sensor on the roof failed, the supplier had gone out of business and we finally found a replacement in Queensland.
In the end I’m still happy with system, the lack of parts is a bit of a worry. However, during the cold month it doesn’t really work while a hot pump would. Would I replace it with a hot pump. Not at the moment. Besides, over time timers/switches that let me use surplus PV energy before it goes into the grid, will be my choice.
Where does ‘waste Heat’ from airconditioning, which we currently tend to just literally throw out the window, enter the equation given the simplicity with which the heat can easily be transferred to water with a passive heat exchanger? It truly is free hot water. I would like to see an article on this and the effects it has in combination with all the hot water systems.
Hi Anthony,
I raise this question and issue in your last topic on this subject because I had not been able to find an answer anywhere. I did not get any answer in that blog either.
What happens with the HP when the ambient temperature gets colder. It appears to to me that within a band the HP continues to deliver the same volume of hot water at the same Lt per hour just uses more kWh. However something else seems to happen when the ambient temperature drops further again as it seems to take between one and a half and twice as long to bring the whole tank up to temperature. What is happening? Does the Lt per hour dramatically reduce by as much as half or does the temperature lift of the water passing through the HP fall so the water has cycle through the tank twice to achieve the desired 60 degree tank temperature? Maybe a bit of both happens. Cannot find the answer anywhere. But it appears to me that below a certain temperature the HP does not deliver the 60 degree water at the spec Lt per hour.
Hi David,
When ambient temperature falls so to does the COP of the heat pump system. When the air outside gets really cold, there’s just less heat energy for the system to grab.
The colder it gets, the harder the system has to work to find that heat. This means it becomes less efficient and can even struggle to keep up with the demand for warmth.
Hope that helps clarify.
Sometimes, parts of the system can even get frosty. When this happens, the system has to pause water heating and deal with the frost, which slows everything down.
Cheap units manage low temperatures by bringing in a conventional element in the tank. Others simply run the fan but not the compressor to try and melt the frost, but of course this stops the water heating cycle.
Household air conditioners sometimes have resistive heating strips in the outdoor unit to deal with frost so they’ll continue to deliver heat, just not efficiently.
David Walsh,
“What happens with the HP when the ambient temperature gets colder.”
See my comments at:
https://www.solarquotes.com.au/blog/heat-pumps-explained/#comment-1579419
https://www.solarquotes.com.au/blog/heat-pumps-explained/#comment-1581814
“However something else seems to happen when the ambient temperature drops further again as it seems to take between one and a half and twice as long to bring the whole tank up to temperature. What is happening?”
The water recirculation pump in my Sanden Heat Pump Water Heater (HPWH) is variable speed. I’d suggest the flow rate reduces with lower ambient air temperatures in order to maintain the HPWH outlet water temperature at 63 ºC. Depending on my hot water usage and ambient air temperature conditions, the unit operates for at least 1½ hours (best case on the hottest summer days) and up to 4¾ hours (worst case on the coldest winter days). An average run is about 2-3 hours to recharge the 250 litre tank.
“But it appears to me that below a certain temperature the HP does not deliver the 60 degree water at the spec Lt per hour.”
In my experience, the HPWH outlet water temperature when the unit is running (feeding into the top of the storage tank) is always hot (except perhaps during the first minute or two after compressor starts-up as the water temperature ramps up to the required operating setpoint, and the return-to-tank water recirculation pipe & connection fittings warm up).
A brass port fitting (insulated except for the strainer hexagon screw cap) in the tank near the bottom (for the water pipe feed to the HPWH) in my system remains cold while the HPWH unit recharges the tank, until the tank is almost fully recharged. Then the bottom tank port progressively warms up to hot. I think the recharge cycle ends when the temperature at the water inlet to the HPWH unit increases to a required setpoint.
Hi David – key advice is to not entertain any heat pump from a manufacturer who can’t/won’t provide graphs of recovery rate and coefficient of performance (CoP) at different ambient temperatures.
These graphs should of course be mandatory within tech brochures.
I have a couple of Australian examples but can’t post snapshots / attachments to this forum. Perhaps Anthony could assist here?
We had a solar thermal unit installed in a new house in 2006. It was an absolute pain frequently overheating and had panels on the roof replaced twice in 6 years. Each time the roof panels failed we were without hot water for about 2 weeks.
In our present house we had a Sanden heat pump installed four years ago and it hasn’t missed a beat. We only run the pump between 1.00pm and 3.00pm so pretty much all the power comes from our Solar Panels.
You only have to run it until 3pm, and you still have hot water for morning showers?? I didn’t realize the tanks were that well insulated.
I have a resistive hot water system and it’s set to run four hours a day – but rarely runs more than two. We’ve only run out when we’ve got guests who have a succession of reeeally long showers (think half an hour!), then we hit the override button we had installed.
But with an oversize tank you can definitively heat all your hot water in under three hours.
I have two resistive HWS units. On most days they heat from solar only, by turning the heating on and off during the times that there is ample production (same way as a Catch Relay works, but with different hardware).
I’m hard-pressed to justify replacing these at EOL with a heat pump:
– it likely will have a shorter life than a resistive unit.
– use more raw materials during production.
– is more complex to recycle.
If the bulk of my heating of hot water was from a non-renewable source I might think differently.
I installed a solar hot water system in 1972 and it is still working I have to clean it every 2 or 3 years the backup booster is used about 4 times a year. Keeping water use to a minimum is the best way to save having to use the booster.
European data on heat pumps is fascinating. The article itself has some great insights into a range of things, and what caught my eye was the graph showing heat pump uptake by country. The Scandinavians lead Europe, and they have some of the coldest climates.
A lot of these are for heating, not necessarily hot water. Heat pumps are essential, but they need to be better bedded down in the hot water industry with reliable products, installation and servicing.
https://www.sustainabilitybynumbers.com/p/heat-pumps
I think solar HWS are a very effective and cost efficent way to reduce costs. In the majority of Australian states
PVC systems can only exploit the visual spectrum of energy from the sun. However nearly 50% of the suns emissions are in the infra-red spectrum. I see this similar to having PVC and a Wind turbine to produce electricity ie utilizing as many sources as resonably practicable.
Hi Anthony, just changing the conversation a little, in last weeks article you hinted at explaining your installation of a H.W.S. at your Mothers house to be revealed this week. I hope it is still coming, maybe next week ?
hi Anthony,
I can’t find the link to the follow-up article – would you be able to post a link?
Bob
Hi Bob,
It’s in the works. Standby.
Of course, heat pumps are not without their drawbacks, but I believe that this is a pretty good option for heating the house. It will not pay off for you quickly, but you are guaranteed uninterrupted operation of the heat pump for 20-25 years, of course, subject to scheduled maintenance. Here you can make an inspection plan https://fluix.io/hvac-maintenance-checklist
We have evacuated tubes with electric boost and plenty of spare PV energy during the middle of the day ( no battery) for about 30% of our hot water we Ned the electric boost which the PV supplies. Our system is over 10 years old and we have saved heaps $$ – no way would I put in RCHP
I live in SA and have been advised by my plumber that I cannot convert from my gas hot water system to an electric storage system with a timer – I would be forced to keep gas or go with a heat pump system. I have a 10kw Solar PV system and have plenty of excess solar and would like to use it to heat the water up between 10am-3pm each day. My intention is to shut off the gas completely to the house, and even though I advised the plumber, he said that he isn’t legally able to do that. Does anyone have any information or a reference to this rule? And if I shut off gas completely, then why can’t I install an electric storage unit?
Hi Pete,
Your plumber is correct. please see link https://www.sa.gov.au/topics/energy-and-environment/energy-efficient-home-design/water-heater-requirements.
However, if you want to install an electric water heater to replace the gas hot water unit, you can ask the OTR (office of Technical Regular) for an exemption and your plumber will be able to install the electric heater for you. (I have done this at the beginning of last year). Make sure you tell them that your intention is to cut off the gas supply all together.
Great article couldn’t agree more I’ve got a green catch diverter set on solar only and a resistive hot water heater and with a 7 cents a kWh fit don’t get a electric bill even though restricted to 5 kw export!
Trouble is in Victoria you can get 1000$ off putting in a heat pump but nothing for resistive!
For all the reasons you mentioned still better with resistive in my opinion !!
I watched with interest your video on the best heatpumps.
One thing people need to be very careful of is their water quality…
I just contacted a heat pump manufacturer and they told me that the water quality in the area I am in South Australia is not suitable to have a heat pump.
He supplied the water quality specs and the quality report from SA Water.
We pay good money for water to damage our appliances and plumbing, how does that work? (That’s a topic for a different forum)
Whilst I wasn’t happy with the news, I was pleasantly surprised by his honesty.
I had contacted other manufacturers before and NOBODY has even commented on water quality.
The issue seems to be the total hardness of the water. Hard water will ultimately damage or clog the heat exhanger.
(So when people blame the manufacturer, perhaps it may be the sales people that need to be dealt with.)
This is the only sales person who has been honest and up front with me.
They will miss out on a sale, but when I change over to rainwater they will be THE people I will purchase from.
As I have mentioned before, service is the only thing that matters in the end.
What’s your postcode, Paul?
Thanks for the interesting series of blog articles on water heating.
When we built in NZ in 2002, we specified a locally made Thermocell solar hot water system. This uses flat plate collectors, each is around 900mm wide and 800 high, internally they have a small copper heat exchanger at the top with the rest of the panel made of steel configured as a heat pipe (the same principle as a laptop cooler) with a working fluid under partial vacuum. The advantage in our cooler climate is they only contain a small quantity of water so are easier to frost proof.
We have 6 in series and they provide 90% of water for 8 months and around 60% during the winter. A resistive element on a thermostat/timer provides a top up at night or cloudy day when required. The frames are angled at around 50% so for our latitude (43.5 S) they are biased to better winter yield.
We are having solar PV installed on the other flatter part of the roof soon, I’d need to think about options if the current SHW system failed and needed replacing. E.g. would it make more sense to add additional solar PV and divert that to the HWC element.
Hi David,
There’s no one size fits all but you’ll notice from the comments section hot water is a deeply held belief…
I still like the evacuated glass tube collector for solar thermal hot water