A pond heater
is necessary in a climate where you have a cold winter. If you have
fish or plants that need to be kept alive during the winter season,
then you need a pond heater or pond deicer. The temperature in the
water should not go below 50° Fahrenheit. You will also need a
pond heater to melt at least a small hole in the ice that forms on
the surface. This will allow the water to be oxygenated during the
winter.
Some pond heaters have filters and air pumps attached to them so
that you can do the work of creating oxygen, filtering out the waste,
and heating the pond all at the same time. Remember that the pond
heater system will be on 24/7 during the winter, so you should look
for a brand that is energy efficient. Solar-powered pond heaters are
not recommended as there is little sun during the winter.