Inverter Pool Heat Pumps Explained
What an inverter pool heat pump actually does, what the labels on the box mean, and whether the extra money comes back.
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An inverter pool heat pump varies its compressor speed instead of switching fully on and off, so it can throttle down to about a fifth of its output and hold your pool at temperature on a trickle of power. That makes it roughly 30 percent cheaper to run than a fixed speed unit of the same size, and noticeably quieter. The catch is the purchase price, which runs anywhere from $341 to $2,500 more depending on which inverter you pick.
Here is what is going on inside the cabinet, and how to work out whether it is worth the premium on your pool.
What an inverter pool heat pump actually does
An inverter changes the frequency of the power feeding the compressor motor, which lets the compressor run at any speed between about 20 percent and 100 percent rather than just stopped or flat out. The fan does the same thing. That is the whole trick, and every other benefit falls out of it.
The numbers off our own spec sheets show the range clearly. The Guardian Platinum 20kW puts out anywhere from 4.2kW to 20.8kW of heat and draws between 0.26kW and 2.78kW to do it. The Guardian Eco Pro 20kW runs 3.7kW to 20.0kW on a draw of 0.27kW to 3.22kW. Both can idle at roughly a fifth of their rated output.
A fixed speed unit has one gear. The Midea M Series 20kW produces 21.8kW and draws 5.3kW, and those are the only two numbers it has. When the pool is at temperature it stops. When the pool drops half a degree it starts again at full power. Warm pool or cold pool, it is the same 5.3kW every minute it runs.
Why running slowly is more efficient
A heat pump gets more efficient the slower it runs, because a slow compressor pushes refrigerant through the same size heat exchanger and gets far more time to transfer heat into the water. Big coil, small load, easy work. Push the same coil at full speed and the physics get harder.
The Fairland Aqua X Essential 21.2kW is the clearest example in our range. At full output its COP is 6.3. At half output the same unit hits 10.8. Same compressor, same pool, same water, and it is delivering 70 percent more heat per dollar of electricity simply because it slowed down.
This is why the inverter saving is real rather than marketing. Most of the time your pool is not being heated from cold, it is being held at temperature, and holding is a small load. An inverter spends the season in its efficient zone. A fixed speed unit spends the season at its least efficient operating point, because that is the only point it has.
Full inverter, DC inverter, step inverter: what the labels mean
The labels are mostly marketing, but three of them do mean different things and it is worth knowing which you are buying.
Full inverter
Full inverter means both the compressor and the fan are variable speed across a continuous range. This is the real deal and it is what you want. The Fairland Aqua X20 AX20-60C and the Guardian Lux-V 20kW are both full inverter.
DC inverter
DC inverter describes the motor type, a brushless DC compressor, and in practice on pool heat pumps it means the same thing as full inverter. The Guardian Platinum and Guardian Lux-V ranges both run Mitsubishi or Panasonic DC inverter compressors. Treat DC inverter and full inverter as interchangeable when you are comparing units.
Step or partial inverter
Step inverter units have two or three fixed speeds rather than a continuous range, and they capture some of the saving but not all of it. Check the spec sheet for a COP range rather than a single figure. If the sheet lists one COP number and one input power number, it is not an inverter no matter what the sticker says.
Fixed speed, also called on off
Fixed speed units run at 100 percent or not at all, and they still make sense on price. The Midea M Series at $3,799 is our best selling heat pump and there is nothing wrong with it. It just earns its keep on the purchase price rather than the power bill. More detail on the Midea 20kW page.
The COP numbers, side by side
Every inverter in our range publishes a COP range rather than a single number, and the spread between the top and bottom of that range is the inverter benefit made visible. Figures below are manufacturer rated at roughly 26 to 27 degree air, current as of August 2026.
| Model | Type | COP range | COP at half output | Sound at 1m | Price |
|---|---|---|---|---|---|
| Fairland Aqua X20 16kW | TurboSilence full inverter | 22.2 to 7.3 | Not published | 41.0 to 46.7 dB(A) | $5,650 |
| Guardian Platinum 20kW | Full DC inverter | 16.4 to 7.5 | Not published | Low noise design | $6,290 |
| Guardian Lux-V 20kW | Full DC inverter | up to 14.5 | Not published | 44 to 56 dB(A) | $7,990 |
| Fairland Aqua X Essential 21.2kW | Full inverter | 14.8 to 6.3 | 10.8 | 45.1 to 57.0 dB(A) | $4,710 |
| Guardian Eco Pro 20kW | DC inverter | 13.8 to 6.2 | Not published | 43 to 54 dB(A) | $4,940 |
| SensaHeat ES Series 20kW | Inverter | 10.8 to 6.2 | 9.1 | 46.3 to 58.1 dB(A) | $4,600 |
| Midea M Series 20kW | Fixed speed | 5.2 flat | No part load | 54 dB(A), 40 in silence mode | $3,799 |
Manufacturer rated figures. Prices are Waternex list prices in AUD including GST, current as of August 2026.
Read the bottom of each range, not the top. A COP of 22.2 is measured on a warm day with warm water and a tiny temperature lift, which is not the condition you care about. The bottom of the range is what the unit does when it is working hard, and even there the inverters sit at 6.2 to 7.5 against the fixed speed unit's 5.2.
Cold air narrows the gap but does not close it
Every heat pump loses efficiency as the air cools, and the inverters lose it too. At 15 degree air the Guardian Platinum 20kW runs a COP of 7.9 down to 5.3, the Guardian Eco Pro 20kW runs 6.9 down to 4.6, and the Fairland Aqua X Essential 21.2kW runs 7.6 down to 4.5. The Midea drops to a COP of 3.6.
So the inverter advantage in cold weather is roughly 5.3 against 3.6, which is still worth having but is a smaller multiple than the brochure headline suggests. If you swim mostly in a Melbourne or Hobart shoulder season, budget on the cold air figures and ignore the big numbers entirely.
Noise is why half our customers actually buy one
An inverter running at low speed is dramatically quieter than a fixed speed unit, and on a small block that matters more than the power bill. The Fairland Aqua X20 sits between 41.0 and 46.7 dB(A) at 1 metre. The Guardian Eco Pro 20kW runs 43 to 54 dB(A).
Decibels are logarithmic, so 44 dB against 54 dB is not a small difference, it is about half the perceived loudness. If the unit sits under a bedroom window or two metres off the neighbour's fence, that gap is the deciding factor and no spreadsheet is going to change your mind about it.
What the inverter premium actually costs
The inverter premium is far smaller than most people assume if you shop by unit rather than by brand. A Fairland Aqua X Essential 21.2kW at $4,710 is a genuine full inverter with slightly more output than the fixed speed Midea 20kW at $3,799. That is $911 for the technology. A Guardian Platinum 20kW at $6,290 is $2,491 more, and you are paying for the metal cabinet, the dual discharge and the 25 year heat exchanger warranty as much as the inverter.
Run the payback on the saving. Our running cost guide puts an inverter on a covered 40,000 litre pool at about $70 a month against $100 for a fixed speed unit, and $190 against $270 uncovered. Over a six month season that is roughly $180 saved covered, or $480 uncovered.
| Setup | $911 premium (Fairland Essential) | $2,491 premium (Guardian Platinum) |
|---|---|---|
| Covered pool, six month season | About 5 seasons | Does not pay back on power alone |
| Uncovered pool, six month season | Under 2 seasons | About 5 seasons |
| Year round heating | About 2 seasons | 3 to 4 seasons |
Based on the running cost figures in our August 2026 guide at 30 cents per kWh. Your tariff, climate and pool will move these.
The honest read: at the $911 end the inverter is close to a no brainer. At the $2,491 end you are buying quiet running, a better cabinet and a longer warranty, and the electricity saving is a bonus rather than the reason.
When a fixed speed unit is the smarter buy
Buy fixed speed if you run the pool for a short season, the unit sits well away from the house, and the purchase price matters more than the monthly bill. Two months a year of heating will never repay an inverter premium, and pretending otherwise is how people end up spending $2,500 to save $60.
Buy an inverter if you heat for four months or more, the unit is close to a bedroom or a boundary, or your pool is uncovered and the heat pump is going to be working most of the time. On an uncovered pool the inverter earns its money fastest, because the load is relentless.
And before either decision, get the size right. An undersized inverter runs pinned at full speed, which throws away the entire advantage you paid for. Our pool heat pump sizing guide covers the volume maths, and if you want the mechanism behind all of this, read how a pool heat pump works.
Inverter models in our range
We stock full inverter pool heat pumps from 7.5kW to 34.5kW. For small pools and spas the Fairland Aqua X Essential 7.5kW at $1,950 and the Guardian Platinum 13kW at $4,390 cover most of it. Mid size pools land on the Fairland Aqua X Essential 17.1kW at $4,140 or the Guardian Eco Pro 20kW at $4,940.
If quiet is the priority, the Fairland Aqua X20 16kW at $5,650 is the quietest thing we sell. Worth knowing: the same inverter logic applies to filtration, so a Fairland InverPro variable speed pool pump at $1,240 cuts the other half of your pool running cost the same way.
Browse the full range in Heat Pumps for Pools & Spas.
Frequently asked questions
What is an inverter pool heat pump?
An inverter pool heat pump is a heat pump whose compressor and fan run at variable speed rather than switching fully on and off. It throttles down to around a fifth of its rated output to hold a warm pool, which uses far less electricity and makes far less noise than a fixed speed unit cycling at full power.
Is an inverter pool heat pump worth it in Australia?
An inverter pool heat pump is worth it if you heat your pool for four months or more each year, or if the unit sits close to a bedroom or a neighbour's fence. A $911 premium over a fixed speed unit pays back in about two to five seasons depending on whether the pool is covered. A $2,500 premium is buying quiet running and build quality more than electricity savings.
What does full inverter mean on a pool heat pump?
Full inverter means both the compressor and the fan vary their speed continuously, rather than only the compressor or only in fixed steps. Look for a published COP range and a range of input power figures on the spec sheet. A single COP number and a single input power figure means the unit is fixed speed regardless of the label.
How much cheaper is an inverter pool heat pump to run?
An inverter pool heat pump costs around 30 percent less to run than a fixed speed unit of the same size, which works out at roughly $30 a month on a covered 40,000 litre pool and $80 a month on the same pool uncovered at 30 cents per kilowatt hour. The saving comes from the unit running at part load, where its COP is far higher.
Is DC inverter the same as full inverter?
DC inverter and full inverter mean effectively the same thing on a pool heat pump. DC inverter describes the brushless DC compressor motor, while full inverter describes the continuous speed range of the compressor and fan. In practice every DC inverter pool heat pump we sell varies both, so the two labels are interchangeable when you compare models.
Do inverter pool heat pumps work in cold weather?
Inverter pool heat pumps work in cold weather but lose efficiency as the air cools, like every heat pump. At 15 degree air a Guardian Platinum 20kW runs a COP between 7.9 and 5.3 against a fixed speed unit's 3.6, so the inverter still wins by a clear margin. The Guardian Platinum and Lux-V ranges keep operating down to minus 15 degrees.
Not sure which one suits your pool? Ask us
Tell us your pool volume, whether it is covered, your postcode, how long a season you want and how close the unit sits to the house. We will tell you whether the inverter premium is worth it on your pool, and which model to spend it on. It takes a minute.
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This guide is general information for Australian pool owners and is not a substitute for advice on your specific pool and site. Efficiency and running cost figures are manufacturer rated and vary with your climate, tariff, pool and usage. Pool heat pumps are electrical appliances and must be installed and connected by a licensed electrician. Prices and specifications are current at the date of publication and change without notice.