How to choose the right solar water heater

Choosing the right solar water heater comes down to four things, and only four: how many people live in your home, how many bathrooms you have, your roof's space and orientation, and how your household actually uses hot water. There's no single model that fits every home — what's enough for a couple in a small flat is nowhere near enough for a villa with three bathrooms and a big family. The mistake we see most often is people shopping for models before they've worked out what they actually need. The order should be the other way around: figure out your requirement first, then pick the heater.

Thing 1: household size

This is the starting point of any real calculation, and the single biggest factor. The more people in the home, the higher the daily hot-water demand, so the bigger the storage capacity needs to be — otherwise someone always ends up finding the tank empty right when they need it. A small household's needs look nothing like a large one, or a home where grandparents or long-staying guests are part of the picture. It's also worth thinking beyond who lives there today: is the household likely to grow soon (a newly married couple planning children, for example)? Changing capacity after installation is far harder than getting the number right the first time. If people in the home travel or are away for long stretches of the year, that's also worth mentioning — it lowers real consumption below the nominal headcount. The exact figure depends on your specific home, not a guess — find your right capacity with the calculator in under a minute.

Thing 2: bathrooms and simultaneous use

It's not just headcount — it's how many bathrooms are in use at the same time. A home where two bathrooms get used together in the morning (one person showering, another washing the kids) needs enough capacity to cover both without the water going cold halfway through. A home with a single bathroom, even with a larger household, sees more sequential use rather than simultaneous demand, so the pressure on the heater is lower. That's why any serious calculation asks about bathrooms before it asks about people in isolation — together, the two are what set the real peak demand, not either one on its own.

Thing 3: the roof — space and orientation

A solar heater needs a spot on the roof that sees the sun for most of the day, clear of shade from trees, buildings, or neighbouring tanks. The longer a spot stays in direct sun, the better it performs across the year — and that difference matters most in winter, when the sun sits at a lower angle. A small or crowded roof, or one that's shaded part of the day, doesn't necessarily rule out installation, but it does affect where and how the unit gets placed — and that's exactly what a free inspection settles on-site, not by guessing from a photo. If you're still deciding whether the investment is worth it in the first place, read is a solar heater actually worth it?

Thing 4: how you use hot water

How does your household actually use hot water — everyone showering in the same morning window, or spread out through the day? Is there a kitchen that draws hot water heavily, or a washing machine running regularly? Heavy, overlapping use needs a bigger storage capacity to cover the peak; light, spread-out use needs much less, even with the same number of people. This is the detail that separates two homes with identical headcount and bathroom count but genuinely different needs.

Mistakes we see often during inspections

Two mistakes come up again and again. The first: calculating only for the household's current size and forgetting that capacity is hard to change after installation — if a change in household size is expected soon, that needs to be said up front. The second: picking the first model seen or the cheapest one, without checking it actually covers the home's needs — which ends up costing more later, when hot water runs out fast and the household either waits or leans on backup electric heating more than expected. The right decision always starts from actual need, not price or whichever model happened to show up in an ad first.

Capacity and the backup heater: why they're calculated together

A solar heater doesn't work alone all year round — cloudy days and winter stretches need help from a built-in electric or gas backup to keep hot water flowing. The capacity you choose has to account for both situations: full solar performance in summer, and heavier reliance on the backup in winter. A correctly sized capacity minimises how much you lean on electricity or gas across the whole year, not just on sunny summer days — and that's exactly what determines how much you actually save. Read more about winter performance specifically in solar water heaters in winter.

Why this decision is worth your time before installation

A solar heater isn't something you replace every year — it has a long service life, and changing or expanding it after installation costs time and effort you don't need to spend if the sizing is right from the start. The time you put in now — working out household size, bathrooms, roof, and usage — is an investment that saves you unexpected problems and costs later. The practical path is simple: start with the calculator for a quick starting picture, then let the free inspection settle the fine details that need a trained eye on-site — the two complement each other rather than replacing one another.

So how do I choose, exactly?

No need to memorise formulas or hunt for generic tables online that give you a number that knows nothing about your home — the calculator does that work using your actual inputs. Answer three questions (home type, bathrooms, household size) and get the right starting capacity for your home in under a minute, then let the free inspection confirm it on-site against your real roof. For more on capacity itself, read how many litres does your home need?, and if you're weighing a flat against a villa, read solar heater for a flat or a villa? Once you've settled on a capacity, you can look at specific models like the Nobel Apollon range — after sizing, not before. And the right choice isn't only about capacity — the company doing the installing and standing behind the work matters just as much, which is its own topic covered in how to choose a reliable installer.

Find your right capacity ← or Book a free inspection and we'll choose the right one after seeing your home.