Is a 20kW Pool Heat Pump Right for Your Pool?
The most popular size we sell, and the one people most often buy for the wrong pool.
Want your exact number? Our pool heat pump sizing calculator uses your pool size, postcode, cover and swimming season to work out the right kW, then shows the heat pumps that fit.
A 20kW pool heat pump suits a standard Australian family pool of roughly 30,000 to 45,000 litres with a cover, in a temperate or warm climate, swimming from about October through to April. That is the honest answer. Outside those conditions the 20kW either sits there half loaded and costs you money you did not need to spend, or it never quite gets the water where you want it and you blame the brand.
20kW is the size that gets asked for by name more than any other. Half the time it is right. This is how to tell which half you are in.
What a 20kW heat pump actually covers
A 20kW heat pump puts roughly 20 kilowatts of heat into the water per hour at mild conditions, which lifts a 40,000 litre pool by about half a degree an hour when the weather is on your side. Over a normal spring day that is two to three degrees of gain, which is exactly what you want. It is not a fast heater. No pool heat pump is. It is a machine that holds a temperature once it gets there.
Here is the practical envelope for a 20kW unit in Australia.
| Situation | Is 20kW the right size? |
|---|---|
| 30,000 to 45,000 L, covered, Brisbane / Perth / Sydney | Yes. This is the sweet spot. |
| Up to 55,000 L, covered, warm climate, summer season only | Yes, it will cope. |
| 30,000 to 45,000 L, no cover, temperate climate | Borderline. Buy the cover, or go 24kW. |
| Under 25,000 L | No. Oversized. Look at 13kW to 16kW. |
| Melbourne or Hobart, swimming past April | No. Step up to 24kW or 28kW. |
| 50,000 L plus, uncovered | No. You will be disappointed. 28kW minimum. |
| Spa only, under 3,000 L | No. Wildly oversized. |
If your pool is not on that list, work it out properly with our guide on what size pool heat pump you need. Volume first, then cover, then climate.
The pool cover changes the answer more than the brand does
A cover is worth more to a 20kW heat pump than any feature on the spec sheet. An uncovered pool loses most of the heat you paid for overnight through evaporation off the surface, so the heat pump spends the next morning putting back what the night took out instead of climbing.
Put a cover on a 40,000 litre pool and a 20kW unit will hold 28 degrees comfortably through the shoulder season. Leave the same pool open and that 20kW is now a 24kW job. People spend two thousand dollars stepping up a size when a few hundred on a cover would have done more. The full argument, with numbers, sits in our piece on pool heat pump running costs.
Ignore the headline COP number when comparing 20kW units
Two 20kW heat pumps quoting COP 5.2 and COP 16.4 are not four times apart in efficiency, they are quoting different things. The big number is peak COP at minimum inverter speed on a mild day, which is the machine idling. The smaller number is COP at or near full output, which is what you get on the cold morning you actually care about.
Compare like for like. Look at the low end of the quoted COP range, not the top. Look for the second performance line at air 15 degrees rather than air 27 degrees, because that is the shoulder season. And check the heating output at that lower ambient, because that is the figure that decides whether the pool gets warm in September.
An example from two units on our shelf. The Guardian Eco Pro 20kW quotes 3.7 to 20.0kW output with a COP range of 13.8 down to 6.2 at air 27 degrees. Drop to air 15 degrees and the same unit gives 2.6 to 14.5kW at a COP of 6.9 down to 4.6. That second set is the honest one.
The 20kW pool heat pumps we sell, and who each one is for
Waternex stocks five heat pumps at or near 20kW, from $3,799 to $7,990. Prices current as of September 2026 and include GST.
| Model | Price | Rated output | Noise at 1m | Best for |
|---|---|---|---|---|
| Midea M Series 20kW | $3,799 | 21.8kW at COP 5.2 | 54 dB, 40 dB in silence mode | Best value. The one most people buy. |
| SensaHeat ES Series 20kW | $4,700 | 20.2kW, COP 10.8 to 6.2 | 46.3 to 58.1 dB | Inverter on a budget, 25 year heat exchanger. |
| Guardian Eco Pro 20kW | $4,940 | 3.7 to 20.0kW, COP 13.8 to 6.2 | 43 to 54 dB | Full inverter, Australian service network. |
| Guardian Platinum 20kW | $6,290 | 4.2 to 20.8kW, COP 16.4 to 7.5 | Low noise, metal cabinet | Cold climates. Rated to minus 15 degrees. |
| Guardian Lux-V 20kW | $7,990 | Full DC inverter, top discharge | Quietest of the range | Tight side yards. Air blows up, not sideways. |
The Midea 20kW is the default recommendation
The Midea M Series 20kW is our top selling pool heat pump and the one we put in front of most people at $3,799. It rates 21.8kW of heating at COP 5.2, drops to 17.0kW at COP 3.6 in cooler ambient conditions, runs on R32, has Wi-Fi and app control, and drops to 40 dB in silence mode. Midea rate it for residential pools up to 70,000 litres, which is optimistic for an uncovered pool in a cold climate but fair for a covered pool up the east coast. Five year warranty on the compressor and heat exchanger. There is a dedicated page for it at the Midea 20kW landing page if you want the full rundown.
Spend more only for a reason you can name
Step up from the Midea to the Guardian Eco Pro 20kW at $4,940 for full DC inverter modulation, a titanium heat exchanger with a 25 year warranty, and a local Australian service network. Step up again to the Guardian Platinum 20kW at $6,290 if you are in a genuinely cold spot, because it runs down to minus 15 degrees where the Eco Pro stops at minus 7. Those are real reasons. A shinier cabinet is not.
When to skip 20kW and go one size either way
Go down to 16kW if your pool is under 30,000 litres, covered, and in a warm climate, because a 20kW in that pool spends its life short cycling. The Guardian Eco Pro 16kW at $4,401 and the SensaHeat ES 16kW at $3,800 both land there.
Go up to 24kW if the pool stays uncovered, sits over 45,000 litres, or you want to swim in July. The Guardian Eco Pro 24kW is $7,010 and the SensaHeat ES 24kW is $5,500. There is also the Fairland Aqua X Essential 21.2kW at $4,710 if you want a little more than 20kW without the jump to a 24. The full range sits in the pool and spa heat pump collection.
Oversizing is the cheaper mistake of the two. An oversized inverter heat pump throttles back and still works, it just cost more than it had to. An undersized one runs flat out every day, never reaches the setpoint on a cool week, and wears out sooner. If you are genuinely torn between two sizes, take the bigger one.
What a 20kW heat pump needs from your electrician
A 20kW pool heat pump is a hardwired 240 volt single phase appliance that needs a dedicated circuit sized by a licensed electrician. The Midea 20kW draws 5.3kW with a maximum current of 23A and calls for a 25A circuit breaker minimum. The Guardian Eco Pro 20kW is specified as a 15A hardwired connection. These numbers differ by model, so the circuit gets sized against the unit you actually buy, not against a blog post.
Plumbing side, allow for the water flow. The Midea wants 8.3 cubic metres per hour through a 50mm connection with a 33 kPa pressure drop. The SensaHeat ES 20kW wants 120 to 150 litres per minute through 40mm. If your existing filtration pump cannot deliver that, the heat pump will underperform and it will not be the heat pump's fault.
Give it airflow too. These units pull a large volume of air across the evaporator and dump it back out colder. Boxed into a narrow side passage with no clearance, the unit re-breathes its own cold exhaust and efficiency falls away. That is the case for a top discharge model like the Guardian Lux-V 20kW, which throws the air upward instead of into the fence.
Frequently asked questions
What size pool does a 20kW heat pump heat in Australia?
A 20kW pool heat pump comfortably heats a covered pool of 30,000 to 45,000 litres in a temperate or warm Australian climate. Uncovered, or in a cold southern climate, the same unit suits a pool closer to 30,000 litres. Manufacturer ratings up to 70,000 litres assume ideal conditions with a cover.
How much does a 20kW pool heat pump cost in Australia?
A 20kW pool heat pump costs between $3,799 and $7,990 in Australia as of September 2026, before installation. The Midea M Series 20kW sits at the bottom of that range at $3,799 and the Guardian Lux-V 20kW at the top at $7,990. Installation by a licensed electrician and plumber is separate and varies by site.
Is a 20kW pool heat pump too big for a small pool?
Yes, a 20kW pool heat pump is oversized for a pool under 25,000 litres. A 13kW to 16kW unit is the better match. That said, an inverter model handles oversizing far better than a fixed speed one, because it throttles down rather than short cycling, so the penalty is mostly the money you spent up front.
Can a 20kW pool heat pump run a spa as well?
A 20kW pool heat pump can run a spa of up to about 3,000 litres alongside a pool, which is what Midea rate the M Series 20kW for. The spa will heat slowly because the system is plumbed and sized for the pool. A dedicated spa heat pump is the better answer if the spa is the main event.
How long does a 20kW heat pump take to heat a pool?
A 20kW heat pump lifts a 40,000 litre pool by roughly half a degree per hour in mild conditions, so a five degree lift takes most of two sunny days from a cold start. Heat pumps are designed to be left running to hold a temperature, not switched on the day before a party.
Which 20kW pool heat pump is the best value in Australia?
The Midea M Series 20kW at $3,799 is the best value 20kW pool heat pump on our shelf, and it is our highest selling unit. It gives 21.8kW of heating, Wi-Fi control, R32 refrigerant, a 40 dB silence mode and a five year compressor warranty for roughly a thousand dollars less than the nearest full inverter alternative.
Not sure? Send us the numbers
Tell us your pool volume, whether it has a cover, your postcode and the months you want to swim, and we will tell you the size. If a 20kW is wrong for your pool we will say so rather than sell you one. Start with a free pool heating quote.
Pool heat pumps are electrical appliances. Installation and electrical connection must be carried out by a licensed electrician, and the water connection by a licensed plumber, in accordance with the manufacturer's instructions and the requirements that apply in your state. Sizing figures in this article are general guidance for Australian conditions and are not a substitute for a site specific assessment.