Pond Water Heaters for Winter Ponds
In cold climates typical of lots of the USA, Canada and Northern Europe tankless pond water heaters are used extensively. In top koi ponds the water heaters are in fact highly sophisticated automatically controlled gas fired tankless water heaters in many cases. For smaller ponds and larger fish tanks immersion or tank water heating is used. In countries where ponds freeze over it is important to keep a hole open in the ice to allow toxic gases to escape. You can easily make a hole (DO NOT BREAK THE ICE AND MAKE NOISE) by placing a pan of boiling water on surface of ice ... this will melt a hole into surface.
It's easier to buy a small heater specially made for the job
Oase also make a very clever item that allows a hole to be kept free of ice ... Oase Pond Vent Ice Reducer
The Pond-Vent pump pulls the lower layer of water (which has been warmed to
around 39 F by the higher temperature of the earth) from the bottom of the pond.
The water is then pumped through the hose, using extremely little energy, and is
let out at the surface directly below the floating bowl. 220 gallons per hour
are being delivered by the Pond-Vent without breaking up the water layers. The
warmth of the water is sufficient to keep a hole with a radius of 11 to 11.5
inches ice free. This allows toxic gases caused by decomposition processes (fish
excrement, leaves, etc.) to evaporate. This aeration process helps ensure the
survival of fish and other microorganisms. In order to operate the Pond-Vent Ice
Reducer properly, the pump, which hangs on the floating bowl, should be 8 inches
above the bottom of the pond. The depth of the pond should be 32 to 40 inches.
The enclosed hose, which connects to the floating bowl, is 32 inches long and
can be shortened if necessary.
Oase pond vent pump ... you'll also find other winter pond products here
Koi Pond Tankless (Gas Fired normally) Water Heaters
This type of tankless water heater is not just to prevent the water from freezing it is meant to maintain a water temperature by continuous heating of around 15 degrees C or 55 to 60 degrees F. At these temperatures koi continue to feed well and thereby continue to put on weight and body condition under the heated water conditions.
When considering tankless gas or electric water heaters design and installation is critically important and expert help should be sought. Materials of construction for the tankless water heater should ideally be stainless steel.
For smaller ponds or koi holding tanks a submersible (immersion type) heater that lies on the bottom of the pond can be adequate. The heater is normally protected in such a way that it does not touch the bottom of the pond or the sides of the tank or pond wall. While plugged in this electrical tankless water heater must always be submerged and the controller must be protected from the elements.
As a rule of thumb (although it depends upon many conditions) you can assume
a kiloWatt (1,000 watts) is enough electric power to heat about 250 US gallons
by 10 degrees F ( about 8 degrees for Imperial gallons) and maintain your tank
or pond at that temperature
Make sure any tank or immersion type heater is electrically protected.