Heaters for ponds

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Last updated July 2014
Water temperature affects many aspects of life – that of fish, especially Koi, and their keepers.

Should you heat an outdoor fish pond?
How warm to keep the water?
Keeping the heat in
How to heat the fishpond
Costs
What heating equipment is available?
Maintenance
Six top tips for choosing outdoor fish pond heaters

First note that heaters like these that create ice-free spots do not radically change water temperature in the whole pool:

Should you heat an outdoor fish pond?

Probably only if you are a Nishigoi (Koi) fish keeper, is the quick answer, and then only after considering the following points.

The seemingly simple decision to heat your Koi pond means…

  • Extra work continuing the summer routine of feeding, cleaning and monitoring equipment.
  • Working outside in the chilly months of the year.
  • Koi being vulnerable to sudden temperature drops if the power or equipment fails.
  • Higher bills.

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How warm to keep the water?


The cheapest option is to just heat the water a few degrees higher than it would be otherwise, to take the edge off the cold British winter. This prevents fish’s metabolism slowing right down (which it will do at colder temperatures because Koi are cold blooded, like other fish and reptiles) and stops your heating bill going sky high.

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Keeping the heat in

To be sure that you aren’t wasting your money heating the surrounding air, covering the pond is a good way to reduce expensive heat loss.

It’s also important to have a winter cover available for emergencies. Floating bubble plastic on the pond’s surface is better than nothing if the equipment or power fails.

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How to heat the fishpond

Specialist equipment and advice is available from specialist koi suppliers, such as Absolute Koi and the East Riding Koi Co.

The power source will heat water that’s pumped through a heat exchanger (as in your domestic immersion heater). Here, hot water flows past the piped pond water so the heat can be transferred to the cooler pond water.

There are various stainless steel heat exchangers with different heating capacities (quoted in kilowatts (kW) or British Thermal Units (BTU)) suitable for raising the temperature of different pond volumes above the ambient temperature. These are available to Koi keepers through specialist suppliers.

Power sources include solar panels (becoming more efficient, smaller and cheaper these days), gas and electricity. The risk of power cuts is a major downside of electricity, so you may need a back-up generator.

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Costs

There’s installation and running costs to think about in addition to the purchase price. Installation of gas-powered equipment is much more expensive than electrical versions because you must have a qualified fitter to make the gas connections, although competent DIYers can position equipment and connect water pipes first to keep costs down.

Some electrical heaters must also be fitted by specialists, and should have a residual current device too. Be sure to check all electrical connections for your own and your fishes’ safety. If you’re uncertain about anything, consult an electrician.

Running costs depend on whether you use the heater round-the-clock, or only as a night heater to prevent the temperatures dipping too far. You’ll need to check your gas and electricity tariffs and calculate costs by multiplying the power requirement by the kilowatt or British thermal unit (BTU) price. To minimise costs, insulate the pond and pipework to limit heat loss.

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What heating equipment is available for an outdoor fish pond?

Choices

  • Heaters with analogue or digital controls, designed for easy installation at the plumbing stage and electrical stage.
  • Compact heaters with a control box that can be sited remotely.
  • Smaller heaters can be installed by DIYers, but those over 3kw need an electrician’s expertise.
  • Swimming pool heaters – once a favourite of Koi keepers, but not designed to heat a Koi pond so only buy from companies that provide specially modified equipment, with components that won’t adversely affect your Koi or be adversely affected by fish and water treatments.

Gas boilers
Gas boilers are worth considering for ponds of over 23,000 litres (5,000 gallons). The initial costs are high, with the expense of a boiler, heat exchanger and the services of a gas fitter. However, running costs could be quite low (you need to check current gas tariffs) and if you can make use of your home’s existing central heating boiler your installation costs will be much lower too.

Monitoring

If you’re into gadgets, you could consider fitting a thermometer with remote readout in the house so you can monitor the situation conveniently, record maxiumum and minimum temperatures occurring daily, and be alerted with an alarm to sound in the house if there are any problems. Browse koi specialists, such as Abolute Koi for different devices.

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Maintenance of fishpond heating equipment

Pond heaters require very little maintenance, but it’s important to check with your supplier about backup by the manufacturer and the availability of spares in case something does go wrong. Once the fish become used to higher temperatures, they won’t like a sudden drop in the middle of winter.

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6 top tips for choosing outdoor fishpond heaters

  • Check weather records for the lowest temperatures in your area over the past few years, and choose a heater that can keep the pond at the desired temperature during such a cold snap.
  • Ask if the unit is weatherproof or needs some protection, and install appropriately.
  • Find out how much the water temperature has to drop before the heater kicks in.
  • Choose equipment with indicator lights so that you know that the heater is operating.
  • If the analogue temperature dial (a clock face) is not precise enough, override it with a digital thermostat so you can select a precise temperature.
  • Fit a remote control so that you don’t have to venture outside.

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