About this site

If you go looking for what a hot water system costs to run in Australia, you find four kinds of source and none of them is quite what you wanted.

• Installer and manufacturer sites have calculators, and every one of them is a lead form with arithmetic attached. The defaults flatter the product being sold.
• Government material is accurate and static — good tables, usually for one state, published as a PDF, with no way to put your own numbers in.
• Comparison sites are built for switching energy plans and treat appliances as an afterthought, often with figures imported from overseas.
• Overseas tools are frequently excellent and entirely irrelevant, because they model different prices, different climates and different rebates.

What was missing was something interactive, Australian, and not selling anything. That is the gap this site is built for.

It personalises

Set your state, your household and — if you want — the rates off your own bill, once. Every calculator, table and worked example on the site recalculates for you, and follows you from page to page. There is no account, and the settings never leave your browser.

It shows the working

Every system in the hot water calculator opens to reveal the whole calculation: heat required, losses, efficiency applied, price per unit. The methodology page lists every constant with its source and the date it was checked.

It is validated against something

Both the hot water and the heating and cooling models reproduce Sustainability Victoria's published Melbourne running costs — twenty-two separate figures across the two, almost all within two per cent — and that comparison is re-run automatically every time the site is rebuilt. It is the only claim of accuracy on this site that you can check without taking our word for anything.

It says the inconvenient thing

A gas water heater currently produces fewer emissions than a heat pump in most of Australia, because most of the grid is still dirty. Gas instantaneous beats a heat pump on cost in South Australia and the ACT. A heat pump replacing an electric tank already on off-peak saves far less than the marketing implies. All three are on this site, prominently, because a calculator you can catch being convenient is a calculator you cannot use for anything.

I built this because I wanted to know what the big things in my own house actually cost to run, and I could not get a straight answer anywhere. Not the hot water system, not the heating and cooling, not the pool pump, not the appliances that quietly run all day. I wanted to see what a decision actually meant before I made it, not after the first bill arrived.

Almost everything I found was facing the wrong way. The calculators belonged to the people selling the thing, with defaults that flattered the product. The accurate material was static, usually a table for one state in a PDF, with no way to put my own numbers into it. The comparison sites were built for switching energy plans and treated appliances as an afterthought. None of it was wrong exactly. It just was not answering my question.

What I wanted was something independent, because independence is what makes the number usable. A figure from someone with a system to sell tells you what they would like to be true. What I needed was what was true for my house, my state and the rates on my own bill.

I also wanted the maths that actually decides things, not just a running cost. You buy a hot water system roughly once a decade and then live with it. So the useful questions are how long it takes to pay for itself, whether the saving survives the wait, and whether that money would do more somewhere else in the house. Those are the calculations on this site, and they are the ones the brochures leave out.

Which means sometimes the answer here is no. If your existing electric tank is on controlled load and still working, the page on heat pumps tells you the payback runs past a decade, which is longer than the unit is expected to last. A calculator belonging to someone who sells heat pumps will never tell you that. Being willing to say it is the whole point.

So that is what this is. Set your state, your household and, if you want, the rates off your own bill, once. Every calculator and every table on the site then re-reads itself against your numbers rather than a national average. There is no account and no sign-up, and your settings stay in your own browser rather than reaching me at all, because none of this needs your data to work.

I built the thing I went looking for and could not find. If it tells you what something in your house really costs, in one place, without anyone selling you anything, it has done its job.

One person in Australia, working on it outside a full-time job. That is worth knowing for two reasons: it means there is no commercial relationship with any installer, retailer or manufacturer to disclose, and it means corrections are handled by the person who wrote the thing rather than disappearing into a support queue.

It also means the reason to trust the figures is not credentials. It is that every one of them is sourced and dated on the methodology page, and that the model is checked against an independent benchmark. That is a better basis for trust than a byline anyway.

Some of it will be. There are several hundred figures on this site, energy prices move quarterly and rebate schemes change with little notice, so the useful question is not whether errors happen but what happens to them.

Tell us through the contact form and you will get a reply. If the figure is wrong it is corrected at the source — the data file every page reads from — so the fix propagates to every calculator, table and worked example that used it in a single rebuild, rather than being patched on the one page you happened to find it on. Where a correction changes a conclusion the site had previously drawn, the prose changes with it.

This is also why the site publishes its own checks. Both the hot water and the heating and cooling models are re-run against Sustainability Victoria's published figures every time the site is built, the pool pump model is re-run against the Commonwealth's own register, and the build fails rather than deploys if any of them has drifted. Those checks exist to catch the errors nobody reports.

Advertising, and in future affiliate links that will be labelled wherever they appear. Nobody pays to appear in a comparison, no result is sponsored, and no installer, retailer or manufacturer has any relationship with this site. The disclosure page sets out exactly how it works and what would have to change for that to stop being true.

Five modules so far: hot water, heating and cooling, appliances, swimming pools and solar. Each one feeds the others — reverse cycle heating is the same technology as a heat pump water heater applied to a room, and a pool pump is simply the largest appliance most houses ever own. The whole-bill page composes all five and answers the question people actually arrive with, which is where the money is going rather than what any one system costs.

Solar was the most recent, and it is the one that made the others worth more rather than just sitting beside them: the solar calculator asks the hot water and pool modules what this household actually uses and prices what moving those loads into daylight is worth. Next is a plan comparison helper.

There is no timeline, because this is a side project and promising dates would be the first inaccurate thing on the site.

EV Running Cost does the same job for electric cars in Australia — charging costs, running costs and the comparison against petrol, built on the same principle that every default figure should be sourced and every one of them should be yours to change.