Heating a pool with a heat pump: sizing, running and fault checks

Yes, you can heat a pool with a heat pump: it draws warmth from the air, so it can stretch the Sunshine Coast swim season into the cooler months. This guide covers how a pool heat pump works, how to size one for your pool, how long to run it, and what you can safely check yourself before calling a licensed technician or electrician.

How a pool heat pump heats your water

A pool heat pump moves heat out of the surrounding air and into your pool water rather than making heat itself. According to AstralPool, a fan pulls outside air across an evaporator coil filled with refrigerant, the refrigerant absorbs that warmth and turns to gas, a compressor raises its temperature further, and a heat exchanger passes the heat to pool water flowing through the unit. Gas and electric element heaters work differently: AstralPool notes they produce their own heat and are rated in megajoules or BTUs.

Heat pump efficiency is described by its Coefficient of Performance (COP). AstralPool’s example is a COP of 6, meaning six units of heat delivered for each unit of electricity used, and a higher COP means lower running costs. An inverter heat pump uses a variable-speed compressor that ramps its output up or down to match demand as the air temperature changes, while a fixed-output unit simply switches on at full capacity and off again. The catch for every heat pump is that it relies on warm air, so output falls and run time rises on cool nights. The other downsides are a slower heat-up than gas and running costs that depend on your tariff and air temperature, which a cover and sensible settings help keep in check.

What size heat pump does your pool need?

A quick starting point is to divide your pool volume in litres by 2,500 to get the heat pump output in kilowatts, then round up to the next model. That rule comes from AstralPool’s sizing guide, which uses a 36,000 litre pool as its example and arrives at about 14 kW. AstralPool also says the formula is a quick reference for extending the season with a pool cover.

Here is the same method applied to a 40,000 litre pool:

1. Measure length, width and average depth. An 8 m by 4 m pool with an average depth of 1.25 m holds 8 x 4 x 1.25 = 40 cubic metres.
2. Convert to litres: 40 cubic metres x 1,000 = 40,000 litres.
3. Divide by 2,500: 40,000 / 2,500 = 16 kW.
4. Round up. If no model is exactly 16 kW, choose the next size above it, as AstralPool advises.

Treat 16 kW as the floor for a covered pool used in an extended season. Madimack, another heat pump maker, warns that a unit sized for an extended season only will not reach its set temperature in the winter months, so year-round swimmers need a fuller assessment. Postcode-based calculators help here: AstralPool says its calculator draws on Bureau of Meteorology historical temperatures for your location. For a running-cost comparison across heating types, see our post on the cheapest way to heat a pool in Australia.

Sizing adjustments for Sunshine Coast backyards: wind, shade, covers and swim season

The litres-to-kW figure is only a baseline, and the right size for a Sunshine Coast pool moves up or down with exposure, shade, cover use and how many months you want to swim. EvoHeat lists pool size, location, weather, desired temperature, shading, wind exposure, cover use and features such as waterfalls, infinity edges or attached spas as the inputs to sizing. The table below shows which way each factor pushes the choice.

AstralPool gives two ways to handle cooler evenings: buy a slightly larger unit, or keep a smaller unit and use a cover whenever the pool is not in use. Madimack says a cover significantly reduces the heat pump size needed. If you are weighing that trade-off, read whether a pool cover is worth it.

Where a heat pump fits against solar and gas

Madimack says a heat pump is designed to maintain pool temperature by running every day, and EvoHeat says one can take over when solar heat falls short. None of the three is the right answer for every pool; the table compares the factors that matter.

For a full look at the roof-collector option, read Solar Pool Heating Explained, and for local system choices see choosing a pool heating system on the Sunshine Coast.

How long to run a pool heat pump and how long it takes to heat

A pool heat pump usually takes one to two days to bring a cold pool up to temperature, then runs daily to hold it there. AstralPool puts typical heat-up at 24 to 48 hours depending on local factors, and Madimack says to expect a rise of 0.1 to 0.3 degrees per hour on first start. On those figures, lifting a pool by 6 degrees takes roughly 20 to 60 hours of running.

There is no single right number of hours per day. The heat pump only runs while your filter pump is pushing water through it, and Madimack says a heat pump is designed to maintain temperature by running every day. An inverter model modulates its output to match demand, while a fixed-output unit cycles on and off (AstralPool). Practical rules:

• Set the filter pump schedule to cover the hours you want heating, since no flow means no heat.
• Daytime or night: warmer daytime air helps output, because heat pumps rely on warm air. EvoHeat notes built-in timers let owners shift run time to match rooftop solar or off-peak tariffs, so the cheapest window depends on your electricity plan.
• Keep the cover on overnight and between swims so the heat you paid for stays in the water.
• Avoid overheating. AstralPool warns that above 28 degrees, especially in winter, algae and bacteria grow faster and use up sanitiser, so test more often and check the pool chlorine and pH levels guide.

Pool heat pump not heating: checks you can safely do yourself

When a heat pump stops heating, start with the setting, flow and airflow checks that manufacturers list, all of which an owner can do from outside the unit. Work through them in order, using only the controller and your pool equipment:

1. Check the mode and set point. Madimack notes that if the pool is already warmer than the thermostat setting, the heater will not run. Some units, such as EvoHeat’s, also have cooling and auto modes, so confirm it is set to heat or auto.
2. Confirm the filter pump is running. Heat pumps have an internal flow switch and will not operate without enough water flow, according to the EvoHeat manual.
3. Clear the flow path. Empty the skimmer and pump baskets and clean or backwash the filter. AstralPool links poor heating to a blocked filter, and Madimack links its E6 temperature-difference error to a filter that has not been backwashed. See sand vs cartridge filters for filter care.
4. Check the pump speed. If you run a variable-speed pump on a low setting, make sure it still gives the heat pump enough flow (Madimack); the unit’s flow switch stops it running when flow is too low (EvoHeat). The variable-speed pool pump guide explains speed settings.
5. Check the valves. If a bypass valve is fitted, check it has not been left set to bypass the heater.
6. Read the error code and look it up in your model’s manual. Codes are brand-specific: Madimack uses E3 for low flow, while EvoHeat’s Fusion-i Pro manual uses E03.
7. Clear the airflow. Remove leaves and debris from around the coil and fan. EvoHeat says to isolate the unit’s power first and brush the fins gently downwards with a soft brush.
8. Check the air temperature. Madimack notes that in cooler temperatures the unit runs longer to reach temperature.
9. Test any water under the unit. In humid weather the EvoHeat manual says condensate can reach several litres per hour. Test it with a chlorine strip: no chlorine means condensation, chlorine suggests a leak.

Stop there. Do not remove panels, touch wiring or attempt anything on the refrigerant circuit.

When to call a technician or licensed electrician

Call a professional as soon as a fault points inside the unit, to its power supply or to the refrigerant circuit, because that work needs a licensed electrician or a licensed refrigeration technician. Queensland’s Electrical Safety Office says to always get a licensed electrician for any electrical work, and under section 18 of the Electrical Safety Act 2002 that includes installing, testing, maintaining, repairing and replacing electrical equipment. The EvoHeat manual is just as direct: units must be connected by a licensed electrician and no unlicensed person should install or repair one.

Work on the sealed refrigerant circuit, such as servicing or repair, needs a national refrigerant handling licence from the Australian Refrigeration Council (ARC) where the unit uses a controlled refrigerant. ARC says national controls cover fluorocarbon refrigerants such as HFCs, and that integrated pool heat pumps need only electrical and water connections at installation. Call a technician when:

• the fan runs but the outlet water is barely warmer than the inlet on the display, even with good flow and clear airflow
• an error code keeps returning after the owner checks above
• water under the unit tests positive for chlorine or salt
• the unit trips power or has damaged cabling, which is a job for a licensed electrician

For pool equipment faults on the Sunshine Coast, start with our pool repair page.

How long a pool heat pump lasts and how to make it last longer

EvoHeat and Madimack do not give a lifespan in years, but their warranties show how long key parts are covered. EvoHeat’s Australian warranty schedule lists 25 years on the titanium heat exchanger, 5 years on the compressor and 2 years on parts for several of its domestic pool heaters, and Madimack also lists 25 years on its titanium heat exchangers. A warranty is not a lifespan, though: Madimack says that with regular maintenance its units should outlast the warranty, and EvoHeat says regular servicing extends life. To get the most from yours:

1. Keep the coil, fan and surrounds clear of leaves, mulch and garden growth.
2. Keep the filter clean so flow stays steady, and switch the heater off while vacuuming, as the EvoHeat manual advises.
3. Keep water balanced; Madimack’s warranty schedule, for example, excludes heat exchanger corrosion or scaling caused by unbalanced water chemistry.
4. Check the condensate drain is not blocked and wipe the casing down with a damp cloth, as the EvoHeat manual suggests.
5. Book a professional service. AstralPool suggests a yearly check and EvoHeat suggests a refrigeration technician every two years, more often for units in coastal areas.

Installing a pool heat pump: placement, plumbing and electrical basics

A pool heat pump should be installed by a pool professional, with the power connection done by a licensed electrician. AstralPool warns that a DIY installation could void the warranty, and EvoHeat says an unlicensed electrical installation will. What an owner can usefully plan is the location:

• Outdoors, close to the filter, with good airflow and nothing blocking the fan, according to AstralPool.
• Clearances. One EvoHeat manual asks for 700 mm to walls or fences at the sides, 500 mm overhead and the unit sited 2 to 7.5 m from the water’s edge. Check your own model’s manual.
• Away from roof run-off. EvoHeat warns against spots where heavy roof run-off pours into the unit, worth noting for wet-season storms.
• Plumbing order. The heater goes after the filter and before any chlorinator or sanitiser, and AstralPool suggests a bypass valve so the filter can run with the heater off.

To talk through sizing or heating options, see Billabong Pool Service’s pool heating page, with pool shops in Noosa, Maroochydore and Caloundra. For more local context, see efficient pool heating on the Sunshine Coast.