A heat pump is the most efficient way to heat a swimming pool with electricity. That’s not marketing; it’s physics. But “a heat pump” covers everything from a basic on/off unit that runs flat out until it trips, to a full-inverter machine that sips power once your pool is warm. They’ll both heat your pool. Only one of them does it without wincing every time the electricity bill arrives.

This article walks through the three things that actually matter when you’re choosing a heat pump: how efficient it is, how fast it will warm your pool in real South African conditions, and what you need alongside it to stop that heat leaking straight back out. We’ll use our two Fairland ranges as the worked examples, because they sit at two different points on the efficiency scale and the difference between them is instructive.

First, what a heat pump actually does

A pool heat pump doesn’t make heat the way an element in a kettle does. It moves heat. A fan pulls outside air across a coil containing refrigerant, the refrigerant absorbs warmth from that air, a compressor squeezes it to raise its temperature, and a titanium heat exchanger hands that heat over to your pool water as it flows through. The air leaves the unit a few degrees cooler than it arrived; your pool water leaves a little warmer.

The reason this matters: the electricity you pay for runs the fan and the compressor. It does not create the heat. The heat was already in the air for free. That’s why a heat pump can put several kilowatts of warmth into your pool for every kilowatt it draws from the wall, and it’s where COP comes in.

COP: the only spec that tells you what it costs to run

COP stands for Coefficient of Performance. It is simply heat out divided by electricity in. A COP of 5 means that for every 1 kW of electricity the unit draws, it delivers 5 kW of heat into the water. A resistance heater, the kettle-element approach, has a COP of 1. Every kilowatt you pay for is one kilowatt of heat, no more.

So when you compare heat pumps, the kilowatt rating on the box tells you how big it is. The COP tells you how cheap it is. Two 13 kW units with COPs of 5 and 9 will warm your pool at the same speed, but the second one does it on a little over half the electricity.

Why the fine print matters

You’ll notice the caveat under those numbers, and it deserves a plain-English explanation rather than being buried. COP is not fixed. It changes with the weather and with how hard the unit is working. The warmer and more humid the air, the more heat there is to harvest and the higher the COP climbs. A cold, dry Highveld morning in August gives a heat pump much less to work with than a muggy Durban afternoon in February.

It also changes with speed. An inverter heat pump running at 20% of its capacity to maintain a pool that’s already warm is far more efficient than the same unit at 100% trying to lift a cold pool by ten degrees. That’s exactly why the peak COP figures for inverter units are quoted at partial load. It’s not a trick; it’s where these units spend most of their life once your pool is up to temperature. But it does mean the honest comparison is this: a full-inverter unit’s worst COP, at full speed on a cool day, is still in the same territory as a basic on/off unit’s best.

The kilowatt rating tells you how fast. The COP tells you how cheap. You’re buying both.

On/off, inverter, full inverter: what’s the difference?

Heat pumps split into three broad families, and the family matters more than the brand.

The on/off unit is the one most people picture when they think of a pool heat pump, and it’s why heat pumps have a reputation for being noisy and hungry. If you’ve been put off by a neighbour’s unit roaring away at seven in the morning, that was almost certainly an on/off machine. We don’t sell them, and this is the reason.

How much warmer will my pool actually get, and how fast?

This is the question everyone wants answered and almost nobody answers honestly, so let’s do the arithmetic. Heating water is predictable. It takes about 1.16 kWh of heat to raise 1,000 litres of water by 1°C. Everything else follows from that.

Two practical conclusions fall out of that example. First, a heat pump is not instant. It is a steady-state appliance that’s happiest running long hours at low speed to hold a temperature, not sprinting to reach one. Plan the first warm-up over a few days, then let the inverter settle into maintenance mode where its efficiency shines.

Second, and more important: the single biggest factor in how fast your pool warms up and how much it costs to keep warm isn’t the heat pump at all. It’s whether you cover the water.

What a heat pump can promise, and what it can’t

Here’s the thing nobody tells you at the point of sale. A heat pump doesn’t give you a pool temperature. It gives you a gain over ambient: a number of degrees above the average air temperature that it can hold once the pool is up to heat. Pick a set point of 40°C in July and the unit will run flat out, cost you a fortune and never get there, and that isn’t a fault. It’s physics.

The reason is that a pool loses heat faster the warmer it is relative to the air around it. A 28°C pool on a 20°C day is losing heat steadily. The same pool on a 5°C night is losing it several times faster, because the gap it’s bleeding across has more than tripled. At some point the unit’s output and the pool’s losses balance, and that’s the temperature your pool settles at. Everything that widens the gap (cold air, wind, no blanket, an undersized unit) pulls that settling point down. Everything that narrows it (a blanket, shelter, a bigger or more efficient unit, warmer weather) pushes it up.

So the honest question to ask about any heat pump isn’t “how hot will it get my pool?” but “how many degrees above the outside air can it hold, and does it still do that in winter?” For a correctly sized inverter unit with a blanket on at night, the answer across most of South Africa is somewhere between 8 and 12°C above the daily average air temperature. In a Johannesburg summer, where the average sits around 20°C, that’s a very comfortable 28 to 30°C pool. In a Johannesburg July, with an average closer to 10°C, the same unit holds the pool in the low twenties: swimmable for the hardy, not a heated spa. A unit that can’t operate in cold air, or that has one speed and can’t run efficiently for long hours, gives up far more of its gain as the season turns.

A heat pump buys you degrees above the weather. It doesn’t cancel the weather.

That’s why the comparison table below has a column for sustainable gain over ambient, and why it matters more than the kilowatt rating. It’s also why the units that keep heating in sub-zero air and modulate down to a trickle hold onto their gain through winter while conventional units don’t.

Why a solar blanket isn’t optional

Here is the uncomfortable truth about pool heating. Most of the heat in your pool leaves through the surface, and the main route out is evaporation. Every litre of water that evaporates off your pool takes a substantial chunk of heat with it. The US Department of Energy puts evaporation at the largest source of heat loss from a pool by a wide margin, and estimates that a cover can cut a pool’s heating costs by 50% to 70%.¹

Read that again in the context of the arithmetic above. A heat pump adds roughly 5°C a day to an uncovered pool and watches a large part of it disappear overnight. Put a solar blanket on and the gains stick. The same pump gets you to temperature in half the time, and then holds that temperature while barely ticking over, which is exactly the low-speed, high-COP regime where an inverter unit earns its keep.

• It protects the heat you’ve paid for. A 500 micron blanket on the water overnight dramatically cuts evaporation, which is where most of your heat pump’s work would otherwise go.
• It adds free heat during the day. A good solar blanket absorbs sunlight and passes that warmth into the water, typically adding several degrees on its own before the heat pump does anything.
• It shrinks the heat pump you need. A covered pool has a much smaller heat load. That can be the difference between needing the next size up and not.
• It cuts the running cost at both ends. Less heat to replace means fewer hours of compressor time, and the hours it does run are at lower speed and higher COP.
• It saves water and chlorine too. Less evaporation means less top-up, and less sunlight on the water means slower chlorine burn-off.

We’ll say it plainly: if you install a heat pump without a solar blanket, you will be disappointed by the running cost, and it won’t be the heat pump’s fault. Every heat pump we sell carries the same note on the product page for this reason. Our TriTherm 500 micron solar blanket is the one we recommend, and pairing it with a roll-up station from our blankets and roll-up stations range is what turns “I should put the blanket on” into a thirty-second job you’ll actually do every evening.

How the Fairlands stack up against the competition

We sell Fairland because, on the numbers that matter, nothing else in the same price bracket comes close. That’s a bold claim, so here it is side by side with two representative competitors sold in South Africa: a premium full-inverter unit from a major international brand that competes with the InverX20, and a popular conventional heat pump from a well-known local air-conditioning brand, the kind that sells in volume at roughly Comfortline money. Figures are the manufacturers’ own published specifications, all measured at the same standard 26°C to 27°C air and water conditions.

Gain over ambient is the temperature a unit can hold above the average daily air temperature once the pool is up to heat, with a solar blanket on overnight and the unit sized to the pool. It’s our working guidance from installations across the country, not a laboratory figure. Uncovered, wind-exposed or undersized installations will achieve less.

Read the top row first. On peak efficiency the InverX20 isn’t ahead by a little; it’s a third more efficient than the best competing full-inverter unit we can find a published figure for, and more than three times as efficient as the conventional units most people end up buying. On cold-weather capability it’s in a league of its own: it keeps heating in air ten degrees colder than its closest rival will tolerate. If running cost and year-round heating are what you’re buying a heat pump for, this is the one to measure everything else against. It’s also the only unit on the list that holds its full gain over ambient through a Highveld winter rather than fading as the air cools.

Now look at the Comfortline against what it actually competes with on price. Competitor B is the sort of unit most South African pools end up with: a solid, conventional on/off heat pump from a brand you’ve heard of, sold through air-conditioning and hardware channels at much the same money as a Comfortline. It has one speed, so its COP of around 6 is the best it ever does. The Comfortline’s peak of 9 is 50% better, and because it modulates all the way down to 20% output, it spends most of its life in exactly the low-speed, high-efficiency zone that a one-speed unit can never reach. Add a spiral titanium exchanger with 30% more surface area, seven-times-quieter operation and the same build quality as the InverX20, and the Comfortline is, in our view, the best heat pump you can buy at its price, and one of very few true inverters available at that money at all.

In its class, the Comfortline is the best heat pump you can buy. Above every class, the InverX20 is the best heat pump, full stop.

Our two heat pump ranges

We stock two Fairland ranges because they answer two different questions. One is the sensible, efficient choice for most pools. The other is for the owner who wants the lowest possible running cost and the quietest possible unit, and is prepared to pay more up front for it.

So which one?

For most pools in most of the country, the Comfortline is the right answer. It is a proper inverter unit with a strong COP, it’s quiet, and the range runs from small plunge pools up to very large ones. The InverX20 costs more up front, meaningfully more, and pays that back in two situations: if you intend to heat through the depths of a Gauteng or Free State winter, where its sub-zero operating range and higher cold-weather efficiency really matter, or if the heat pump will sit near a bedroom window or a neighbour’s wall and silence is worth paying for. If neither applies, put the difference toward a blanket and roll-up station, and you’ll be warmer for less.

Getting the most out of your heat pump

A heat pump is only as good as its installation and the way it’s run. These are the things that separate a happy owner from a frustrated one.

1. Give it air

   The unit heats your pool by stripping warmth from the air passing through it, so it needs a lot of air. Leave clear space in front of the fan outlet and around the intake, never box it in, and don’t let it recirculate its own cold exhaust. A unit crammed into a corner under a lean-to is working with one hand tied behind its back.

2. Fit a bypass

   The heat pump plumbs in after your filter, on the return line, with a bypass so you can regulate flow through it and isolate it for servicing or winter draining. Too much flow is as bad as too little; your installer will set the bypass so the exchanger sees the flow rate the unit is designed for.

3. Run it with your filter pump, for longer than you think

   A heat pump only heats while water is flowing, so your filter pump needs to be running whenever the heat pump is. Inverter units want long hours at low speed, not short bursts at full. If you’re on a timer, extend it. A variable-speed pool pump makes this painless and cheap.

4. Set a sensible temperature and leave it there

   Every degree above 28°C costs disproportionately more to hold, because the gap between water and air widens and the pool loses heat faster. Pick the temperature you actually want to swim in, set it once, and resist nudging it up. The app makes it easy to drop it a few degrees when you’re away.

5. Put the blanket on. Every night.

   If you take one thing from this article, make it this. The blanket is the difference between a heat pump that quietly holds temperature on a trickle of power and one that fights the night sky and loses. With a roll-up station it takes less time than brushing your teeth.

Frequently asked questions