Air Source Heat Pumps

Find your pond heater

Use pond size as a shortlist, then read the model description for its recommended volume and operating temperatures. A covered pond at 12°C is our winter planning target; supplier volume guides are not a guarantee for every installation. Contact us for help choosing a model for your pond.

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Heating type

Rated heat output

Wi-Fi control

Heating control

Power supply

Air discharge

Brand

Air Source Heat Pumps for Koi Ponds

Choose a heat pump for your pond, your season and your target temperature

A pond heat pump transfers heat from outdoor air into circulating water. Use it to extend the feeding and growing season—warming earlier in spring and maintaining warmth further into autumn—or to hold a chosen temperature throughout winter. These are different heating duties, so choose for your target temperature, intended season and the pond’s heat loss.

Covers, insulation, exposed surface area, local weather and outdoor pipework all affect the heat your system needs to replace. Our pond-size bands use supported supplier guidance where available. Not every model has a published winter pond-volume rating. If a model has no numerical pond-size band, contact us with your pond details so we can help check its suitability.

Compare the model’s heating output at stated conditions, temperature settings, water flow and electrical supply. Inverter and fixed-speed controls respond differently to changing demand; horizontal and vertical air discharge need different installation clearances. A three-phase model also requires a suitable three-phase supply. The buying guide below explains these choices so you can make a useful shortlist.

For other heating methods, explore our complete pond heating range. If you need help choosing, send us your pond dimensions, cover and insulation details, location and target temperature.

Find out more about heat pumps

Choosing the Right Heat Pump for Your Pond

How to use the pond-size filter

Choose your pond-volume band to build a shortlist, then read the individual model’s sizing guidance and technical specifications. The figures do not all use identical test conditions. A supplier’s general kW sizing table is not automatically an exact-model winter pond rating: the output at lower air temperatures must be checked. Thermotec Apex, Edge and Nova bands use the supplier’s published pond-volume maxima for the exact model. Those maxima should not be read as a guarantee of maintaining 12°C through every winter.

A model is included in a numerical band only where the whole band falls within the published volume limit. Above 30,000 litres, check the model’s actual maximum carefully: that filter option is open-ended, but the heater’s capacity is not. Compare the installation’s heat loss and the heater’s minimum and cold-weather output before choosing; selecting a larger model solely because it appears in the results does not establish that it is the best match for a smaller pond.

For models without a published winter pond-volume rating, ask us to help check suitability for your installation. Give us your pond volume, surface dimensions, cover and insulation details, location and target temperature so we can help assess the installation. A swimming-pool volume rating or a warm-weather kW figure must not be substituted for a winter koi-pond capacity.

Compare control type, Wi-Fi and electrical supply

Inverter models can vary compressor operation within their working range as demand changes. Fixed-speed models cycle on and off in response to their controls. Compare purchase price alongside performance at relevant conditions, installation requirements and your intended use. Wi-Fi can make checking and adjusting the controller convenient, but the unit still needs reliable circulation and regular physical inspection.

Check the electrical specification of the exact model. Some smaller units are supplied with a UK plug; other models require a professionally designed hardwired circuit. Larger options may use single-phase or three-phase supplies. Similar model names do not make these versions interchangeable. Have the proposed supply checked before ordering if its suitability is uncertain.

Water flow, pipework and outdoor positioning

The circulating system must deliver the heater’s required water flow after allowing for the installed pipework and fittings. A pump’s headline maximum is not the same as the flow reaching the heater. Plan isolation, service access and an appropriate bypass arrangement with your installer. Check the supplied unions and connection sizes before choosing additional fittings.

Heat pumps need outdoor airflow. Leave the clearances specified in the model’s manual, avoid recirculating cooled discharge air, and provide a stable base with condensate drainage. Horizontal and top-discharge designs require different space around and above them. Also consider access for delivery, the unit’s weight and future servicing.

Browse established heat pump ranges

Remora Professional · Remora Inverter · Jetline Premium · AquaForte AquaMini

Compare individual Remora and Jetline models

Remora Professional

Open the individual model pages to compare heating output at stated conditions, water flow and electrical requirements. Match the heater to the pond’s heat loss and intended season.

Remora Inverter

Open the individual model pages to compare heating output at stated conditions, water flow and electrical requirements. Match the heater to the pond’s heat loss and intended season.

Poolex Jetline Premium Fi

The single-phase Jetline manual specifies a 15–40°C heating setting range; the dedicated 155 Tri and 210 Tri manual specifies 8–40°C. Select the exact electrical version and check its controller range. A 12°C setting alone does not establish winter heating capacity: pond heat loss and cold-weather output must also be assessed.

Compact vertical Thermotec Apex models

The Thermotec Apex 8kW Inverter Pond Heat Pump and Thermotec Apex 11kW Inverter Pond Heat Pump offer a vertical air discharge arrangement for installations where the necessary overhead clearance is available. Compare their individual water-flow and electrical requirements with the horizontal Edge range below. Their operating limits and nominal ratings do not establish the heat available to your pond on the coldest days.

Compare Thermotec Edge models

Choose the electrical supply and water flow as carefully as the nominal heating rating. The comparison uses normal output at 15°C air and 26°C water where confirmed; these test figures are not guaranteed winter pond capacities. See each model for installation guidance and current pricing.

Model Normal output at A15/W26 Recommended flow Electrical supply
10.5kW single phase 1–8.1kW 4.5m³/h Single phase
13.8kW single phase 1.2–10.3kW 5.9m³/h Single phase
17kW single phase 2.5–13kW 7.3m³/h Single phase
20.5kW single phase 1.8–16kW 8.4m³/h Single phase
21.5kW three phase 2.4–18.5kW 10.0m³/h Three phase
25kW single phase 3.3–20.2kW 10.9m³/h Single phase
30kW single phase 3.3–24.2kW 12.4m³/h Single phase
30kW three phase See model guidance 12.4m³/h Three phase

Estimating electricity use without guessing

Start with electrical input, not the heating output in the model name. Energy used in kWh equals average electrical input in kW multiplied by running hours. For an illustrative calculation, a heater averaging 1kW for ten hours uses 10kWh; at an example tariff of 25p per kWh, that costs £2.50. Your actual tariff, weather, defrost cycles and inverter operation will change the result. Allow separately for circulation-pump electricity and avoid treating a laboratory maximum COP as an all-winter average.

Compare the larger Thermotec Nova models

The Nova range offers larger capacities, including distinct single-phase and three-phase versions. Check the exact electrical supply, water flow and performance at your intended operating conditions. A larger headline rating is not a substitute for assessing winter heat loss.

Seasonal swimming-pool heating: Thermotec Neo

If you are comparing equipment for a swimming pool and extending its usable season, explore the Neo models below. Keep this separate from selecting dependable winter pond heating: do not transfer a swimming-pool volume rating to a covered koi pond at 12°C. For year-round pond requirements, begin with the pond-focused ranges and a complete sizing assessment.

Compare individual Remora F models

Compare the separate Remora F models for their heating performance, water flow, controller settings and electrical requirements. Select for the heat loss of the actual installation rather than nominal output alone.

Compare individual Poolex Silverline Top models

The upward air discharge needs clear space above the unit. Compare the exact single-phase or three-phase model and its installation requirements. The operating-air limit does not by itself establish a winter pond capacity.

Compare individual Poolex Nano FI models

These compact models have distinct heating and automatic control ranges. The manual specifies 15–40°C in heating mode and 7–40°C in automatic mode. Check the intended operating mode before selection; neither the pool-volume guide nor the low operating-air limit confirms a 12°C winter pond capacity.

Single phase and three phase explained

Single phase is the usual UK domestic supply, typically 230V. Three-phase models need a suitable three-phase supply, commonly 400V between phases, and cannot use an ordinary domestic socket. Single-phase does not automatically mean plug-in: many heat pumps require a dedicated hardwired circuit. Have an electrician check the exact model’s connection, current and protective-device requirements.

Fixed-speed and inverter operation

A fixed-speed heat pump runs its compressor at one speed when heating, then switches it off when the controller is satisfied. An inverter can vary compressor speed within its operating range to match changing demand. Compare performance and noise at the same test conditions; actual running costs depend on heat loss, weather, water temperature and electricity tariff as well as control type.

Horizontal and vertical air discharge

Horizontal-discharge units blow cooled air out through the front or side; vertical-discharge units send it upwards. Check the clear space around the inlet and outlet in the model’s installation manual. Top-discharge equipment needs clear space overhead, while horizontal discharge needs space for air to disperse in front or beside it. Avoid enclosing either design where it draws its own cold discharge back through the inlet.

Understanding rated heating output

Heating output is the heat delivered to the water, measured in kW. It is different from the electrical input consumed by the unit. Manufacturers quote performance at particular air and water temperatures; warm-weather maximum output must not be treated as guaranteed winter output. Use the detailed tables to compare like-for-like test conditions and have the expected cold-weather duty checked before choosing a heater.

Seasonal heating or heating throughout winter?

Extend spring, summer and autumn

Seasonal heating helps you warm the pond earlier in spring and prolong the warmer period into autumn. The aim is a longer period of suitable conditions for feeding and growth, rather than a promise of a particular growth rate. Temperature, fish condition, stocking, filtration and water quality all influence the result. Make changes gradually and follow an appropriate feeding programme.

If winter heating is not part of your plan, follow the heater manual’s winterisation procedure before freezing conditions arrive. Some installations need the heater isolated and drained. Stopping the heater does not mean switching off essential pond filtration or aeration: plan the pond’s winter operation separately.

Maintain a stable winter temperature

Year-round heating needs a heater that can operate at the expected outdoor temperature and still deliver enough heat to offset losses from the pond and connected equipment. Covers and insulation reduce heat loss, but exposed filters, pipework, wind and surface area still matter. A swimming-pool volume rating at warm air and water temperatures is not a winter koi-pond capacity.

Why heat a koi pond through winter?

Koi are cold-blooded: their body temperature follows the surrounding water. As the pond cools, metabolism, appetite and digestion slow down, and some immune responses become slower too. Heating gives you more control over these seasonal changes and helps maintain a more consistent environment. Its value is about managing the fish’s condition as well as keeping ice off the pond.

Why do we use 12°C as a winter target?

For our covered-pond winter comparisons, 12°C is a moderate target aimed at avoiding the much colder conditions of an unheated winter pond while keeping heating demand below that of a warmer growth-focused regime. Compared with colder water, a milder winter environment can support greater activity and more opportunities for appropriate feeding. Feed according to the fish’s appetite, the food manufacturer’s temperature guidance and the capacity of your filtration, rather than the thermometer alone.

There is an important distinction: 12°C is not an immune-system on/off switch. Carp research shows that antibody responses can still occur in colder water, but may take much longer. Holding 12°C therefore does not mean immunity is fully active or that the fish are protected from disease. It is a husbandry target, not a medical threshold.

The spring “danger window”: why temperature matters for fish health

The concern behind the danger-window advice is real: disease organisms and a fish’s defences do not all respond to warming water at the same rate. Fish coming out of winter may be in poorer condition, while some infections can develop in cool water when parts of the immune response are still slow. That can make the transition into spring a vulnerable period.

However, there is no single temperature band in which every parasite or bacterium becomes active, and no temperature above which they all stop being a problem. Different diseases favour different conditions. Maintaining a chosen temperature helps you manage the environment, but does not replace quarantine, good water quality, observation or diagnosis when fish show signs of illness. Avoid sudden temperature changes, and do not simply turn up the heater as a treatment for an unidentified problem.

Why choose 15°C or above for feeding and growth?

Around 15°C and above, koi generally become more active and able to make better use of feeding than in cold winter water. That makes 15°C a useful starting point for an extended feeding and growing season: heating earlier in spring and maintaining warmth further into autumn gives the fish more time in conditions that support growth.

It is not the optimum temperature for maximum growth. Published common-carp guidance places best growth in warmer water, broadly in the twenties Celsius, with the exact result depending on the fish and their conditions. Think of 15°C as a more active feeding regime rather than a guarantee of rapid growth. Genetics, age, diet, stocking and water quality all affect the outcome.

As feeding increases, so does the load on the filter. Warmer water also holds less dissolved oxygen, while fish and biological filtration need oxygen. Match the feeding programme to aeration and filtration, and monitor ammonia and nitrite as conditions change. Raising temperature without supporting the rest of the pond does not automatically improve fish health or growth.

Match the heater to your chosen temperature

A heater sized to maintain a covered pond at 12°C is not automatically sufficient to hold the same pond at 15°C or a warmer growing temperature. Higher targets increase heat loss and running demand. Check the model’s cold-weather output and heating setpoint range: a controller with a minimum heating setting of 15°C cannot be used as a 12°C heating-only option. Covers, insulation and exposed filters all affect the capacity required.

Compare electrical input as well as heating output

Heating output is the heat delivered to the water; electrical input is the power consumed to produce it. Both depend on operating conditions. Check the exact model’s supply phase, manufacturer-specified circuit protection and installation instructions. A running-current figure below 13A alone does not establish that a standard UK socket is suitable or that a plug is supplied.

Ice prevention is a different job

A floating ice preventer maintains a local opening in the surface; it does not maintain the whole pond at 12°C or 15°C. For this purpose compare the Oase IceFree4Seasons circulation unit with the Oase IceFree Thermo 200. For controlled whole-pond heating, compare our air source heat pumps.