Top quality hand selected
Japanese Koi Carp at sensible prices

Dormer Cottage, Spurgrove Lane, Little Frieth,

Nr. Henley on Thames, Bucks, RG9 6NU

Phone/Fax: 01494 882600

Koi Pond Heating Equipment

At Koi Water Garden, we are able to offer competitive prices on not only high quality koi, but also on koi related goods such as Hydro Pro Air Source Heat Pumps, electric heaters, heat exchangers, and other accessories.


last updated 21st December 2019



Shop online with confidence via our secure on-line shop.
We accept all major credit cards!

Review your Shopping Cart - click below.

Heating your Pond - is it necessary? - What's the best method?


Well frankly - NO - you don't have to heat a koi pond. Koi are poikilothermic, which means their body temperature is governed by the surrounding water temperature. They are hardy 'coldwater' fish which will withstand and proliferate in a wide range of water temperatures. Koi have been known to survive temperatures of 1 Deg C (33 Deg F) up to 32 Deg C (90 Deg F) without ill effect. It is not the extremes of temperatures which seem to bother Koi, but rather the duration of any temperature extremes and rapid temperature fluctuations which can cause problems for the Koi keeper.


In the UK, the problems are generally not associated with extremely cold water temperatures during winter, but rather the length of our rather dreary, 'cold' and miserable winters and low water temperatures which cause problems. A Koi's immune system functions properly at temperatures over around 12.5 Deg C ( 55 Deg F). Under this and the immune system ceases to function effectively and at lower temperatures, a Koi's ability to fight diseases can be severely reduced. Unfortunately, many pathogenic bacteria and a range of parasites can survive and even proliferate at temperatures down to around 5 Deg C, meaning that your Koi are at their most vulnerable at temperatures of between 6 Deg C and 12.5 Deg C.


As water temperatures in the UK can be in this range for up to 5 months of the year, you will appreciate why it is that most of the disease problems with which we as Koi keepers are faced (generally in Springtime) may be precipitated by this length of relatively cold water temperatures.


In addition, smaller ponds of say, 2000 gallons or less will be more prone to the affects of unstable water chemistry as the pond volume is comparatively small and even in ponds with a larger volume but of a shallow nature can exhibit the same problems. Any water parameters which change too quickly will stress the Koi. One of these water parameters is obviously water temperature, and ideally, this should not fluctuate by more than 0.5 deg C per day.


Over winter, and indeed in Spring, we may get very cold and frosty nights, but followed by sunny days, which can result in temperature fluctuations of up to 2 deg C or even more in small, unheated, shallow and uncovered ponds. The degree of temperature change obviously varies across the UK but one of the most important benefits of heating a Koi pond is the ability to achieve a stable water temperature at all times.

The objective of any heating installation is therefore not to heat the pond to high temperatures for reasons of, for example, high growth, or just to keep our koi active. It should be targeted at controlling the water temperature to avoid the temperature 'trap' or the fluctuations described above.


In our own installations, we heat our stock (and private) ponds until Christmas time, by leaving the pond thermostats set to 16 Deg C ( 61 Deg F). This extends the Koi's Summer and keeps them feeding and growing well. From around the turn of the new year we then progressively turn down the temperature by 0.5 Deg per day until the water temperature returns to ambient levels (whereby the water temperature falls to match the surrounding average air temperature). We then give all our Koi a shortened winter for about 1/2 of January and all of February and then switch the heating on again at the beginning of March. During these cold months we allow the water temperatures to drop as low as we can , normally down to 4 or 5 Deg C. This does absolutely no harm to healthy Koi for this short period but helps to 'cleanse' the pond environment and reduce the numbers of any remaining parasites or bacteria.

 This means that we are effectively giving the Koi a 10 month Summer and a maximum two month Winter. We are also only using our heating systems for around 4 - 5 months of the year, and not heating at all for the two coldest months, January or February, and since we are not trying to raise our pond temperatures to ridiculously high levels, we are also reducing extra fuel bills as much as possible.

 It is an established and accepted fact that Koi live longer if given a 'natural' winter, and we do NOT subscribe to the view that Koi ponds must be heated all the year round to ensure their well being. Indeed we would go further, in that ponds that are heated all the year round must be maintained much more carefully to avoid problems as the Koi never get a period of 'rest' or inactivity and a Summer maintenance regime is absolutely vital to ensure that no problems are encountered. Weekly water changes and filter maintenance must be adhered to whilst water temperatures are elevated simply because whilst you are providing a warm comfortable environment for your Koi, you are also providing the same conditions for parasites and bacteria which can and often do multiply very quickly in ponds kept 'warm' during winter, whilst the not so vigilant Koi keeper is snuggled up in front of a log fire with ample supplies of mince pies and Brandy, completely forgetting about daily or even weekly pond maintenance tasks!


 If you do decide to heat your pond you will have a number of options, including heating using gas, oil, electricity and now electricity in the form of air source heat pumps. Whilst Gas installations are more expensive to install, they are comparatively cheap to run.   Oil is now becoming very expensive, and the capital outlay for an oil installation is generally also more expensive than a gas installation. Direct electric heating systems are easy and relatively cheap to install, but are the most expensive to run - Now however with the introduction of air source heat pumps, you have the ability to increase the efficiency of your heating system installation by up to 400% as air source heat pumps can deliver up to 13 times the energy consumed and are now by far the cheapest method of heating your pond ( see below). However - the choice is yours!


To give you an idea of costs, Gas systems can cost as little as 70p per thousand gallons per day to run, whilst oil is currently around £1.00 per thousand gallons per day, and direct electric heating costs start from around £1.30p per thousand gallons per Day.

 DC inverter air source heat pumps can cost as little as 50p per thousand gallons per day.


Insulating a heated pond is vital for keeping costs under control and even a simple cover made from a heat retentive material such as bubble wrap or (ideally) polycarbonate will reduce costs substantially. As an example we have halved the costs of heating our 25,000 gallons of stock ponds by covering all the heatedponds with triple wall polycarbonate sheet. The costs of the insulation will pay for itself in the first season.




Digital Thermostats.

A necessity if you heat your pond, gives very accurate control down to + or - 0.1 Deg C resolution. Fully adjustable, weather proof (splash proof) and ideal for Gas or Oil installations. Complete with thermostat probe cable (5 metres) and power connections. LED display. Not suitable for the control of direct electric heaters.




Type Price
Pro-line digital £142.50
 Digital thermostat

Digital Thermostats - relay controlled.

A necessity if you heat your pond using direct electric heating, gives very accurate control down to + or - 0.1 Deg C resolution. Fully programmable , weather proof (splash proof) and can also be used for Gas or Oil installations. Complete with thermostat probe cable (5 metres) and power connections. LED display. Suitable for use with mains powered heaters up to 3kw. .




Type Price
Pro-line digital £205.50
Digital thermostat

Stainless Steel Heat Exhangers

These are made from high grade stainless steel and incorporate thermostat probe pockets and 1.5" or 2" male threaded pipe fitings.


Capacity/Max flow Price
60,000 btu, 900 gph £250.50
100,000 btu, 1440 gph £265.50
130,000 btu, 1860 gph £295.95
170,000 btu, 2460 gph £319.50
230,000 btu, 3300 gph £385.50
460,000 btu, 6600 gph


 stainless steel heat exchanger

Floating Digital Thermometer

This super floating digital thermometer reads in Centigrade and is really neat. Solar and battery powered. Supplied with tethering cord.




Model Price
solar digital £17.95

IR Infra Red Pocket Thermometer

This super little pocket thermometer reads remotely by using Infra Red technology - just point at the water and press the button to get an accurate and instant reading of water temperature. No probe, no wires, no contact with the water. Powered by 2 x AAA batteries, the unit utilises an LCD display which reads from -50 and + 350 deg C, with a resolution of 0.1 deg C - the unit comes complete with batteries. Reads in Celsius or Farenheit.


Model Price
IR Pocket £19.95

Pro-line Stainless Steel pond heater systems.

These all new heater units have stainless steel heating elements for good resistance to chemicals, especially salt in the pond water, and therefore have a long life. Accurate to + or - 0.1 deg C the special thermostats have an internal relay that allows them to be used on a wide range of applications including gas and oil boilers as well as electric heaters up to 3kw. These units represent very good value for money indeed. To calculate the correct heater size you will need 1kw per 1000 gallons. All the units in this range can be connected to a normal domestic 13amp mains supply.

 These new Pro-line heaters also offer ultimate flexibility in that the heaters and thermostats can be used independently. Should either unit fail, they can therefore be replaced individually and systems can be upgraded from 0.5kw to 1kw to 2kw to 3kw using the same thermostat.




Model Price
2kw, 9 amp £399.00
3kw, 13amp £419.00
2kw, 9 amp, Element only £188.00
3kw, 13 amp, Element only £196.00
 Pro-line heater

Cloverleaf pond heater systems.

The New Cloverleaf Pond Heaters are fully EU, TUV and UL approved they are available in two size 1kw and 2 kw. The Cloverleaf Heaters are very easy to install into new or existing pond setups and come complete with both rigid or flexible pipe connections. Choose from connection via 19mm, 25mm, 32mm or 38mm flexible pond hose using the 2 hosetails supplied or alternatively the units will accept 40mm rigid solvent weld or 1.5” rigid pressure pipe. These simple easy to use pond heaters have a minimum flow rate of 4000lph and have a safety low flow shut off switch for peace of mind


1kw and 2kw power consumption 4000lph minimum flow rate with pressure switch Thermostatically controlled IP55 rated 1.5m cut end cable fitted Flexi hosetails plus Solvent weld inlet and outlets length 230cm, width 18.5cm, hight 18.5cm  


Model Price
1kw, 5 amp £134.00
2kw, 9amp £154.00
 Pro-line heater

Elecro Titanium in-line heaters.

These units have accurate digital thermostats (except Nano) and Titanium heating elements for ultimate corrosion resistance AND can accept water flow through either direction thanks to the newly designed exterior flow switch. Accurate to + or - 0.1 deg C. To calculate the correct heater you will need 1kw per 1000 gallons. Units up to 3 kw can be connected to a normal domestic mains supply. For kw ratings in excess of 3 kw, heavy duty circuits will be required. All heaters come with 1.5" female threaded end caps for connection to existing 1.5" pipe work (either solvent or pressure) IP 20 rated, will need protection from inclement weather. The smaller analogue, Nano models can be mounted either vertically or horizontally.




Pack Size Price
Nano 3kw, 13 amp £335.00
Nano Titanium 3kw, 13 amp £395.00
2kw, 9amp £529.00
3kw, 13 amp £549.00
4kw, 17 amp £580.00
6kw, 25 amp £625.00
8kw, 34 amp £679.00
 Elecro titanium in line heater

Hydro-Pro Inverter Heat Pumps.



The latest inverter heat pumps from the Hydro-Pro range year are not only super efficient, but are very competitively priced. They are whisper quiet, being among the quietest heat pump range we have yet found, largely because they use ABS casings that do not amplify noise or resonate like a conventional metal body. They can be controlled down to 6 deg C for use through Winter and have accurate electronic controllers that will prevent large temperature swings - VERY important for Koi Ponds.


What is a heat pump?:- A device that converts electrical energy to kinetic to thermal energy through the use of compressed refrigerant. It works like a refrigerator in reverse. It draws heat from the air, and transfers that heat to the pond water. A heat pump does not create heat like a resistance heater, it extracts heat from one location and transfers it to where it is needed.

Heat pumps operate on the principle of a closed circuit similar to that used in the household refrigerator. One side is cold the other hot. For instance a refrigerator removes heat from its inside as well as from the food, and transfers it via the condenser to the outside air, which is warmed.


The latest Inverter Heat Pumps utilise the sun’s free heat by collecting and absorbing energy from the outside air. This energy is then transferred to the koi pond water. Your existing koi pond pump circulates the water through the heater which warms the pond. The unit contains a fan that draws in outside air and directs it over the surface of the EVAPORATOR (energy collector). The liquid refrigerant within the EVAPORATOR coil absorbs the heat from the outside air and the refrigerant becomes a gas. The warm gas passes through the compressor where it is compressed to form a very hot gas, which then passes through the CONDENSOR (water heat exchanger). It is here that the heat exchange occurs as the hot gas gives up the heat to the cooler koi pond water circulating through the coil. The pond water becomes warmer and the hot gas is cooling down as it flows through the CONDENSOR coil, returns to its liquid form and, after passing through the expansion valve, the whole process begins again.


Depending upon the design of the installation and ambient temperatures, it is possible to get in excess of 13 times more heat per kw of power consumed using the latest heat inverter heat pump technology. So for every 1kw of power consumed, up to 13kw of heat can be produced to heat the water.


Inverter heat pumps are the latest type of heat pump to be made available and are up to 30% more efficient than a standard A/C heat pump. This is because DC (direct current) technology is around 96% efficenet compared to A/C technology (alternating mains current) which is only around 46% efficient. In addition, with DC technology the compressor within the heat pump can change speed as the heating demand varies, so that when an inverter unit is first switched on, it will run at full power. As the water temperature approaches the set point, it will slow down and run at a lower power rating and within the set temperature range the heat pump will be running at a low power level, therefore consuming far less electricty. With an A/C model, the unit is either on or off, and when on and running the unit will run at full power. So inverters are able to vary the load to suit the heating requirement and therefore will cost considerably less to run than even their A/C counterparts.


Until now Inverter models have been much more expensive to buy, so have not been commonly used in Koi pond heating, however now these new inverters are very competitively priced, and indeed cheaper to buy than many of the old technology A/C models. These inverter units are also offered with a two year parts and labour warranty which is backed up by nationwide distribution and so now has never been a better time to invest in these super efficent units.


All types of Heat pumps are at least 3 times more efficient than other heating methods including gas, oil, and direct electric. Savings in terms of running costs can be as much as 70% less than for direct electric heating, and up to 40% less than oil or gas.

If you do decide to heat your pond, air source heat pumps are undoubtedly by far the most cost effective method of doing so, being economical to purchase and install when compared to gas or oil installations as well as being cheaper to run, and are way way cheaper to run than direct electric systems.


Hydro-Pro Air Source Heat Pump models.


These models are represent the latest technology in heat pumps, and have COPs up to 13 (coefficient of performance) measured at 25 deg C ambient air temperature. Heat Pumps are very simple to install, just interrupt the pump flow line so that the pond water flows through the heat pump on its way back to the pond. Then just plug in and switch on.

Model Inverter 7 Inverter 11 Inverter 16 Inverter 19 Inverter 24 Inverter 29
Heating Capacity (max kw) 7 11.5 16 19 25 30
Max Input power (kw) 1.10 1.77 2.67 3.17 4.25 5.0
Max Current (amps) 4.7 7.9 11.2 14 18.6 12.7
Power Supply single phase single phase single phase single phase three phase three phase
COP at 15 deg C 7.2 7.2 7.2 7.2 7.2 7.2
COP at 25 deg C 13 13 13 13 13 13
Recommended max pond size (gallons) 5000 9000 12000 14000 18000 24000
Heat Exchanger Titanium Titanium Titanium Titanium Titanium Titanium
Compressor Inverter Inverter Inverter Inverter Inverter Inverter
Inlet/Outlet Connections 50mm 50mm 50mm 50mm 50mm 50mm
Nominal Flow rate cu.m/hr 2.5 3.0 4.0 5.0 6.0 9.0
Refrigerant R32 R32 R32 R32 R32 R32
Dimensions L x W x H mm 1009*370*559 1060*450*691 1060*450*691 1134*444*872 1061*452*1256 1061*452*1256
Weight (kg) 54 68 78 98 117 128
Noise Level DBA 40-50 40-52 40-54 41-56 41-56 42-60
Price 1395.00 2060.00 2795.00 3375.00 4295.00 4795.00


[Back to Top]