Choosing the right pond heater

Compared to other pond hardware such as must-have items such as a pump and filter, a pond heater is an optional purchase (depending on your budget and your approach to koi keeping).

Why consider buying a pond heater?

Better for your Koi? Our cold-blooded Koi have no choice but to respond directly to the temperature of their pond. When ponds freeze in winter they would benefit from a pond heater.  So naturally, during the colder months, when water temperatures fall below 8C, Koi become lethargic and stop feeding until the spring weather warms your pond up again. Heating you pond will mean your koi will be active all through the winter months. A heater can also remove some of the heartache over winter, allowing us to control our pond environment, reducing the extremities and duration of an inhospitable winter. It will also enable us to interact with our koi for longer each year.

Pond heaters are becoming a must have for you fish pond, get one here…

Heating strategy.

Koi keepers and koi professionals that choose to heat their ponds over winter (many still do not) will differ in their approach in how they use the heater.

1. An artificial summer, 24/7. The pond is heated to summer temperatures (18C) when ambient is insufficient to sustain a warm temperature.

2. Remove harsh extremities. A thermostatically controlled heater is used to prevent koi from experiencing a prolonged, harsh winter, setting it at 10C

3. Controlled natural winter. For those koi enthusiasts who believe (and I am one of them) that koi not only require but benefit from a winter period, then a pond heater can be used to reduce the length of a natural cold period, setting it to heat the pond for all the winter barring a 4 week period of natural ambient winter temperature.

Assuming you have one of the above 3 strategies in mind for your own koi, you will need a means of heating your pond. Inevitably, there are cost implications, installation issues and various options of how to heat your pond. Once we have explored the options, you will be in a position to decide whether such a project is achievable and affordable – and whether you consider the benefits outweigh the costs.

The options:

1. Electric heating:

Electric is the most straightforward to install and heats the pond water directly and efficiently. For many years, swimming pool heaters were used to heat koi ponds. They were (and still are) relatively straightforward to install and easily available in a range of sizes to suit different pond volumes. Dedicated koi pond heaters are made from complex stable materials containing titanium, making them super-resistant to chemical attack. All other associated casing and pipework is also made resistant to chemical attack. The criteria for choosing an electric pond heater are similar to those when choosing a UVc (i.e. based on pond volume). They are also installed in a similar way.

Because electric heating is a very direct method of heating, it is regarded as an efficient method of heating your pond (i.e. a high proportion of the energy used by the heater actually heats the water of the pond). This does not however necessarily mean it has a low running cost as this is determined by the unit cost (kilowatt-hour) of electricity.

Option 2 – Heat exchanger with hot water supply.

Compared to electric heating, heating your pond using a boiler is indirect and less efficient (but because of the relative cost of gas, and may still prove to be a cheaper alternative). The capital outlay will be significantly greater than using an electric heater as there is considerably more hardware to purchase and install. Furthermore, the installation is less likely to be a DIY project, requiring a CORGI registered gas installer to connect a new boiler to a gas supply. And compared to the single pumped circuit of an electric heating system, the boiler heating system typically has two: One for the hot water circuit running between the boiler and the heat exchanger and the other between the heat exchanger and the pond. These two pumped circuits are completely independent and will not (and must not) come into contact with each other. (see diagram)

What you will need.

Heat exchanger. The hot water from the boiler comes through one pipe, into the exchanger (which is engineered to have a large surface area for heat exchange), dissipates it’s heat into the counter-flowing cold current of pond water. The heated water cools down and returns to the boiler ready to be heated up again while the warmed pond water returns to the pond.

The boiler. A boiler it is required to produce the hot water circuit that will be pumped through the other channel of the heat exchanger. To determine the size and output of boiler required (again measured in BTUs) you will need to work back from the volume of your pond. For example, a 2000 gallon pond will have a 1000 gallon per hour turnover of water, suiting a heat exchanger of 70,000 BTU. Consequently, you will need to install a boiler with a gross output of at least 70,000 BTU. However, sometimes boilers are rated by their power input rather than their gross output. If this is the case then as a rule of thumb, allow approx. 80 per cent efficiency so that if an output of 70,000 BTU is required then choose a boiler of approx 90,000 BTU input for that system.

How is heat output of a boiler or heat exchanger measured?

The power output capacity of a heat exchanger will be described in BTUs (British Thermal Units) which in turn will be related to a recommended flow rate of pond water through the unit.. At the top end of koi pond heat exchangers, 460,000 BTU will take a flow rate of 4600 gallons, suiting a pond up to 10,000 gallons. Pond water will be pumped through one channel of the heat exchanger continuously (just as it would do through a UVC).

Questions you should ask when considering a heating system.

1. What size of heater do I need?

This will be based on the volume of your pond. The heating capacity of an electric heater is measured using their power consumption – in Kilowatts. A heat exchanger is measured in BTUs (British Thermal Units)

2. How easy is it to install?

This will depend largely upon your existing pump and filter set-up. It is arguably easier to install an in-line electric heater in a pump-fed system (due to the likelihood of there being exposed and accessible pipework). If you have installed a separate UVc, then you will have the skills to plumb in an inline heater. Check which additional pipe fittings you will need. For a heat exchanger, you will need to consider where you are going to position it – and where your supply of hot water will come from and the route it will take to your pond. You may need to invest in an additional boiler.

3. What about the installation?

Electric Heater: You may have read about the new legislation relating to new electrical installations. As of 1st January 2005, new electrical installations, including those in gardens now come under Building Regulations. This means that to comply with your local authority’s building control, for any new circuits (replacement sockets do not count) you will need to notify building control. If your heater is less than 3Kw, then the existing electrical feed is likely to be sufficient. For heaters >3Kw, you will need to install a new electric feed, directly from your home’s consumer unit / fuse box. If you are anything like me, you will be reaching for your yellow pages to find a qualified electrician to do the job. A ‘competent person’ registered with Part P of the building regulations (holding EAS certificates) will be able to issue you with a Building regulations Certificate of Compliance – freeing you of the regulatory burden.

Heat Exchanger / boiler. If you are confident with your hot water plumbing skills, then you can install a heat exchanger yourself. However, if you need a new boiler, you will need to employ the services of a CORGI registered gas installer.

4. Heat control.

Thermostat. This is essential for giving you control over the temperature of your pond. Look out for the sensitivity of the thermostat (i.e. at what increments it can be set to turn on and off). Also check to see how easy it is to read and set. Is it a dial or is there a digital read out?

Timer. Some electric heaters are available with a timer. However, a thermostat should be sufficient to maintain the required temperature – making a timer of little use.

5. Construction and Durability.

How will you house the heater or heat exchanger? Can the model be left open to the elements? What materials is the model made from? Are these safe and inert and therefore suitable for koi? Don’t assume that swimming pool heaters are safe to use in a koi pond. What guarantee come with the unit? Is that competitive? What are the terms of the guarantee? i.e. what will happen in the event of a breakdown, which in most cases will be an emergency?

6. Cost. What is the likely cost of the unit, its installation and running costs?

Calculating the running costs are easier for an electric heater. The running costs will be a function of the cost of electricity (measure in Kwh) and the duration that the heater is on. This period will be governed by the thermostat setting in relation to ambient temperature.

For example: For a 2000 gallon pond, running a 2Kw electric heater over the 4 months from November to February. Assuming that the heater will be working 18 hours each day (this will vary depending on the temperature required) and that 1Kwh costs 10p:

120 days x 18 hours = 2160 hours

2160hours x 2Kw = 4320 Kwh

4320 Kwh x 10p/Kwh =£432


Inevitably, where water comes into contact with extreme heat and in an area of restricted flow, solids will tend to accumulate around the internal surfaces of a heat exchanger or heater. They should be plumbed in with easily removable couplings so the units can be serviced and rinsed out. Depending on the type of heat exchanger, some can be completely stripped down.

Boxout: Things you need to know about your own pond when researching pond heating options.

1. Volume

2. Existing pipe diameters (for matching up pipe-fittings)

3. Proximity and route to suitable electricity supply or hot water supply.

Boxout: The Costs for a 2000 gallon pond.

Gas-fired Boiler Option* Electric Heater Option

1. Hardware:

Boiler £600 2Kw heater £300

Heat Exchanger £170

2. Installation

Corgi Installer £300

Plumbing + Elec Labour, Plumbing + Electrical

Sundries £300 Sundries £300

Subtotal £1370 Subtotal £600

Assuming it will be installed in an existing outhouse or garage.

3. Running Costs

It’s not possible to calculate or even estimate these as it depends on the heating strategy employed and the external / ambient temperatures.

1. Heat output

2. Level of control

3. Relative running costs

4. Purchase can installation costs

5. Safety and reliability.

Heat Exchangers:

‘Architectural Stainless Ltd’ are stocked by most koi dealers as the preferred heat exchanger. (I can’t find any contact details – perhaps they don’t want contacting direct?).

What size heat exchanger or electric heater will I need?

Please note these figures are for ‘rule of thumb’ purposes only. When buying a heater, as with a filter or a pump, if in doubt, always buy the bigger option.

Kill blanketweed and string algae.