Heat pump or solar geyser? A plumber's honest answer

A geyser blanket, a timer, a heat pump or a solar geyser each fix a different problem. They're not interchangeable. Far-south homeowners do best to sort the geyser first, then pick what fits.

Interview by Tomek Korzeniewski · with Zaid Petersen, Owner and master plumber

Key takeaways

• A heat pump stops working when the power is off, while a solar geyser keeps heating as long as the sun is out.

Why a geyser blanket and timer are worth trying first

So before you spend big, start cheap. He won't sell anyone a heat pump or solar setup that doesn't make sense for their house.

The honest answer depends on three things: the house, the people in it and how long they plan to stay. Take one retired person in a flat with a quick morning shower. A fancy system takes a very long time to earn its keep there. Petersen would rather fit a blanket, a timer and a low-flow shower head.

Here's what this means for you. The newest system isn't automatically the right one. A blanket is a morning's job. It's the first thing Petersen would do in any house. It won't change your life, but it starts saving you money the same day. The reason that day-one saving works comes down to what the blanket actually does to the heat slipping out of your old geyser. For wider background, see Saving electricity (City of Cape Town).

What actually slows the heat loss from an old geyser

A blanket slows down standing losses. Petersen explains that a geyser keeps water hot all day whether you use it or not. In a cold, damp roof space down here, that tank bleeds heat the whole time.

The fix is simple. A decent blanket on the geyser cuts that loss, especially with lagging on the first couple of metres of hot pipe. Lagging is just insulation wrapped around the pipe. It keeps heat in the water instead of letting it leak into the roof.

Petersen calls this the first thing he'd do in any house. It's quick. It's cheap. And it works on the geyser you already own. Sorting the tank itself comes before any talk of a bigger system, whether that's a heat pump or solar geyser.

How a timer matches hot water heating to your routines

A timer is the second cheap fix. It means the element only runs when you tell it to. Petersen points out that most families use hot water in the morning and the evening. There's no reason to heat it at two in the afternoon when the house is empty.

He sets the timer to switch on an hour or two before people wake up. Then again before the evening showers. The catch is you have to be honest about your routine. Got teenagers who shower at random times? A timer can leave someone with a cold shower.

Press it and you get hot water now, outside the set hours. When a routine shifts, he adjusts the settings rather than ripping the timer out. A timer and a blanket cost little. A heat pump is a bigger spend, so it only makes sense once the numbers add up.

When a heat pump earns back its running cost

So when do the numbers add up? A heat pump pays off when a household uses a lot of hot water every day. Petersen describes it as a small air conditioner in reverse. It pulls heat out of the outside air and puts it into the water. That uses a fraction of the electricity an element needs for the same hot water.

Think four or five people, lots of showers, a bath, washing up by hand. It also makes sense when your existing geyser is healthy and has years left.

Here's the limit he's firm on. If the geyser is on its last legs, fit the heat pump later. Putting a new heat pump onto a rusty tank is like putting new tyres on a car with no brakes. Sort the geyser first, then spend on the pump. If a heat pump does suit your home, Heat pump installation is the service that handles it.

Where a heat pump unit needs room to breathe outside

Set it up right and a heat pump needs an outside spot with airflow. Petersen says it has a fan and a compressor, so it makes a hum. Not loud, roughly like a fridge. But enough that you don't want it under a bedroom window or hard against the neighbour's wall.

He looks for a position close to the geyser so the pipe runs stay short. Short pipes mean less heat lost on the way to the tank. In Kalk Bay and Simon's Town, with narrow plots pressed against the mountain, finding that spot takes some thought.

Worth knowing: the sea air matters too. Salt eats aluminium fins. A solar geyser sits outside too, but the sun, not the salt, is what shapes where it goes.

The two types of solar geyser and why roof shade decides it

Solar comes in two main kinds: flat-plate panels and evacuated tubes. Both sit on the roof and heat your water with the sun. Petersen also splits them into direct and indirect systems. In a direct system the household water runs through the panel. An indirect system is different. It uses a separate fluid loop with antifreeze to carry the heat across.

Shade decides whether solar works at all. Petersen looks for a roof facing north, or close to it, with no big trees or mountain shadow in the middle of the day. That's the catch across a lot of the far south. Parts of Kalk Bay, St James and the upper side of Fish Hoek lose the sun early in winter because the mountain sits right behind them. Tokai and Constantia have beautiful old oaks that shade half the roof.

Before he quotes solar, he goes up and looks. If the roof loses sun after two o'clock in June, he tells the customer straight. It gets cold on clear winter nights on the Noordhoek and Kommetjie side. That's why he leans towards indirect systems there. A heat pump doesn't care about shade. Sometimes that's the deciding point. Solar geyser installation is the service for the roofs that do suit it. For further reading, see Full text of "SANS 1307: Domestic storage solar water heating systems"Hamburger iconInternet (archive.org).

Why solar systems still need a backup element in winter

Solar does the heavy lifting in summer. Not in a grey Cape winter week. So the element stays in place as a backup.

The backup sits on a timer. It tops up only when the sun hasn't done the job. Set it up badly and the element fights the solar all day, heating water the panels were about to heat for free. Petersen calls this the most common mistake he sees.

Here's the real point. A solar geyser isn't solar instead of electric. It's solar first, electric as the fallback. Sort the geyser first, get the timer right and the element barely runs through summer. But the sun going quiet is one thing. The grid going quiet is another and every Cape Town home knows that worry well.

What each system does and doesn't do during a power cut

A solar geyser keeps heating when the power is off, as long as the sun is out. A heat pump, on the other hand, stops when the power stops, the same as an element does.

Batteries change the maths, but not the way people expect. If someone has a battery backup for the house, Petersen usually tells them not to put the heat pump or the element on it. Hot water is a big load. Better to heat the water when the grid is on and keep the battery for lights, the fridge and the internet.

The choice comes back to his four questions. How many people live in the house, how long you're staying, what state the geyser is in and where the sun falls on your roof. Answer those honestly and the right fix, blanket, timer, heat pump or solar, tends to pick itself.

Ready when you are

If you would like to take this further, Heat pump installation is the place to start.

About the expert

Zaid Petersen, Owner and master plumber, Klipspringer Plumbing.

Frequently asked questions

Should I get a tube or a panel solar geyser?

It comes down to your roof and your water pressure, not just which looks neater. Flat-plate panels are usually the cheaper option and work fine on most roofs. Evacuated tubes handle cold, cloudy days a bit better but cost more and can be fussier with low mains pressure. The right call depends on your roof pitch, your pressure and your budget, so it's worth getting someone to actually look at your roof before deciding.

How long does a 150 litre solar geyser take to heat up?

There's no fixed time, because it depends on the sun you're actually getting that day. On a clear day with full sun on the panel, a tank can heat through in a few hours. On a grey Cape winter day it may barely budge, which is exactly why the backup element is there to top it up.

What's the main downside of a heat pump?

It needs electricity to run, so when the power is off, it's off, the same as any electric element. It also needs an outside spot with airflow, which isn't always easy to find on a small plot. And if your geyser tank itself is old and rusty, fitting a heat pump onto it doesn't fix that problem, it just adds cost to a tank that needs replacing anyway.

Will a plumber rush this job because they're already thinking about the next one?

A proper job on a water heater means checking your roof, your routine and the state of your geyser before anyone picks a system. If a quote arrives without anyone looking at those things first, that's worth questioning. Take your time with the decision. It's your hot water for years to come, not a five minute fix.

Will I get overcharged for something small, like fitting a timer?

A timer is a small, simple job compared to a heat pump or solar install and the work involved doesn't change much from house to house. What should change the price is the access, the wiring and whether a manual override switch gets added. Ask for a number before anyone starts and check that the final invoice matches what you were told.

Will someone actually turn up when they say they will?

That's a fair worry if you've been let down before. Ask for a time window when you book and keep the WhatsApp thread as your record of what was agreed. A business that's confident in its timing will give you a window without hedging.

Could I end up with a big invoice for work that doesn't even fix the problem?

That happens most often when a system gets fitted before anyone checks whether it suits the house. A heat pump on a dying geyser, or solar on a roof that loses the sun by midday, wastes money without solving anything. Ask what was actually checked before the quote was written, not just what was quoted.

If my geyser bursts, will I get the paperwork my insurer needs?

Most insurers want photos of the damage, a written description of what failed and a proper invoice before they'll pay out. Ask whoever you call to photograph the geyser before they start work, not just after and to put the cause of the failure in writing on the invoice. Keep that paperwork together in one place, because insurers often ask for it more than once.

What happens if I call and nobody picks up?

Try WhatsApp instead of a phone call. A lot of smaller plumbing outfits run their day job-to-job and can't always answer a ringing phone, but a message with a photo of the problem lets them reply between jobs instead of losing the message entirely.

I've phoned big companies before and never heard back. Is this different?

A small local outfit lives or dies on its name in the area, so a missed call costs more than it would for a call centre. That's not a guarantee, but it's worth asking anyone you're considering how quickly they usually respond and checking what other homeowners nearby say about it.

What if the plumber who arrives doesn't actually know heat pumps or solar systems?

Ask before you book, not after someone's on your roof. A vague answer or a quick push toward the most expensive option is worth treating as a warning sign.

What should I have ready before I ask about a water heating change?

Know how many people live in the house and roughly when everyone showers. Know how long you plan to stay in the property. Take a photo of your current geyser, including its age if you know it and a photo of your roof showing which way it faces and whether anything shades it at midday. Those answers are what actually decide which system fits.

About the author

Related articles

• Is a heat pump worth it in cape town

  Four quick checks to see if a heat pump suits your household

  Read the guide

From Klipspringer Plumbing

• Heat pump installation in Cape Town, with an honest answer first

  We check if your house actually suits a heat pump before we quote one.

• Solar geyser installation in Cape Town, priced honestly before we start

  A straight answer on solar from a photo of your roof, before any quote