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