Inverter vs On/Off Pool Heat Pumps: Which Is Better for Your Pool?

If you’ve been looking at ways to keep your swimming pool warm, you’ve probably noticed there are two main types of heat pumps available. There are the older on/off models, and then there are inverter heat pumps, which have become increasingly popular.

On the surface, they do much the same job. Both take heat from the surrounding air and transfer it into your pool water. The real difference is in how they run, and that can make quite a difference to the amount of electricity you use.
The real difference is what happens inside the machine once it starts running.

That difference can have a noticeable effect on your electricity bill.

How does a standard pool heat pump work?

A traditional on/off heat pump is fairly straightforward.

With a standard on/off heat pump, things are pretty straightforward. When the pool gets too cold, the compressor kicks in and runs at full power. It stays that way until the water reaches the temperature you’ve set, then it switches off. Once the pool cools down again, the whole process starts over.. Then it switches off.

When the water cools down again, the compressor starts up and the process repeats.

There is nothing particularly wrong with this type of heat pump. It is a proven technology and usually costs less to buy. The drawback is that the compressor has only two settings: **full power or off**.

It cannot slow down when the pool is nearly at the temperature you want.

What does an inverter heat pump do differently?

An inverter heat pump is able to change the speed of its compressor according to what the pool actually needs.

When you first start heating a cold pool, the unit can work harder to get the temperature up. Once the pool gets close to the temperature you have selected, there is no reason for the heat pump to keep running flat out.

The inverter slows down.

This is where much of the energy saving comes from.

Instead of repeatedly switching between full power and completely off, the heat pump can settle into a lower output and maintain the pool temperature without using more electricity than necessary.

It is a bit like driving a car. You don’t accelerate as hard as possible all the way to your destination and then slam on the brakes. Once you are at the speed you want, you ease off and maintain it.

An inverter heat pump does something similar.

The big difference is energy consumption

For most pool owners, this is probably the part that matters most.

Heat pump efficiency is measured using something called COP, or coefficient of performance. It tells you how much heat the machine can produce compared with the electricity it uses.

A conventional on/off pool heat pump might achieve a COP of around 4 under favourable conditions. In other words, 1 kW of electricity could produce roughly 4 kW of heat.

An inverter heat pump can do considerably better when it is running at reduced output. Depending on the model and the conditions, some inverter systems can reach COP figures of up to around 16 at low operating speeds.

That does not mean it will run at COP 16 all the time. Weather, humidity, pool temperature and the speed at which the compressor is running all affect the result.

The important point is that an inverter has the ability to operate much more efficiently when the pool only needs a small amount of heat.

Why this matters over a whole swimming season

Think about what happens after your pool has reached the temperature you want.

The pool doesn’t suddenly need the same amount of energy it needed when it was cold.

It may only lose a small amount of heat through evaporation, wind and the surrounding air. A standard heat pump still has to switch on at full power when the temperature drops enough.

An inverter can reduce its output and replace that lost heat gradually.

That means it can spend much of its time running gently rather than repeatedly starting at full power.

Over weeks and months of pool heating, those differences add up.

Inverter heat pumps also have a softer start

There is another advantage that doesn’t get quite as much attention.

A conventional on/off heat pump can draw a significant amount of current when the compressor starts. An inverter unit uses a softer start, gradually bringing the compressor up to speed rather than hitting the electrical supply with a large startup demand.

This can be useful in homes where the electrical supply is already working hard, particularly when the heat pump is being used alongside other appliances or a solar PV system.

And they tend to be quieter

Because an inverter heat pump doesn’t have to run at full speed every time it operates, it can also be noticeably quieter when maintaining the pool temperature.

Once the water is where you want it, the compressor can slow down.

That is a worthwhile benefit if your pool is close to your home, patio or entertainment area. Nobody wants the sound of a heat pump running at full power when they are sitting outside enjoying the pool.

So, which one should you choose?

If the initial purchase price is your main concern and you only intend to heat the pool occasionally, a standard on/off heat pump may still make sense.

But if you use your pool regularly and want to keep the water at a comfortable temperature for longer periods, an inverter heat pump is worth serious consideration.

The higher purchase price is offset by the way the unit operates. It uses less electricity when maintaining the pool, starts more gently, generally runs more quietly and can adjust its output instead of constantly working at full capacity.

For a pool that is going to be heated regularly, that difference can become important.

Make your pool heating more efficient

At SunScan, we supply inverter pool heat pumps because we believe there is little point in using more electricity than necessary to keep a pool comfortable.

The technology allows the heat pump to respond to the pool rather than simply running at one fixed speed. When more heat is needed, it works harder. When the pool is close to the desired temperature, it backs off.

That is the real advantage of inverter technology.

You are not just buying a heat pump that heats your pool. If required these units can cool your pool in those very hot climates where pools reach uncomfortably high temperatures.

You are buying one that can adjust how hard it works to do the job.

And when a pool heat pump may run for many hours over a swimming season, using electricity more intelligently can make a substantial difference to the cost of keeping the water warm.