How can I heat a hole in my pond efficiently in the winter without using a pond heater?

Question

I'd like to heat my pond to create a hole in the ice during the winter to help a few goldfish survive. The fish are not expensive but I'm trying to save them. The pond is about 50 gallons, about 12 inches deep at the most. Pond is a commercial stiff liner that is kidney-shaped.
I've seen the pond heaters use a lot of energy, 1500 watts or more.
I have an aquarium heater and I might try that but those can be 1000 watts or more. But I'm concerned it will not survive a 100% duty cycle in mid winter.
I'll be using 120vac to heat the pond. Glow plugs seem to all use 12vdc so that's not a great option but I can convert 120vac to 12vdc.

Is there a more efficient way to turn electricity into heat to just keep an open hole in the ice in the pond? I am familiar with basic electronics and make LED lights as a hobby.

Thank you.

Resistive heaters are as close to 100% efficient in turning electricity into heat as you're going to get. — brhans, Sep 19 '19 at 11:18
@brhans Not true; heat pumps can be much more efficient than resistive heat. (Although it would likely be silly to set up a heat pump for a 50-gallon pond...) — Daniel Griscom, Sep 19 '19 at 15:56
@DanielGriscom Of course it is still true to say that resistive heaters are 100% efficient - it's just that heat pumps can be 300% efficient. — Martin Bonner supports Monica, Sep 19 '19 at 16:10

score 1 · Answer 1 · answered Sep 19 '19 at 12:58

The only way to be "more efficient" than a resistive heater is to use a heat pump, and the upfront cost will probably make that a non-starter. Resistive heat is 100% efficient, a heat pump can be 300% efficient. Either way, you are fighting the weather and it takes a lot of energy.

Getting a big horse watering trough (or, given the size of your pond, a small watering trough, or an actual aquarium) and moving the fish into the basement (or perhaps living room, etc. with the aquarium option) for the winter will be far less costly than melting ice all winter.

score 0 · Answer 2 · answered Sep 19 '19 at 10:36

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Instead of using heat and letting it all escape you can use a insulated dome to provide a non-iced over spot.

answered Sep 19 '19 at 10:36

ratchet freak

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Pond is kidney-shaped. Would the dome have to fit over the whole pond? If the dome fits over the whole pond then gas exchange would be decreased due to the seal. The fish need open water for gas exchange. They can survive the cold liquid water temps. Do you have a picture of your idea? – Bulrush Sep 19 '19 at 10:40
no only over a small part, And if you are really worried about gas exchange you can put in an bubbler with airstone. – ratchet freak Sep 19 '19 at 10:51

score 0 · Answer 3 · answered Sep 19 '19 at 13:18

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Moving water doesn't freeze unless it's extremely cold. Perhaps a small fountain or bubbler in the middle of the pond would keep it open.

answered Sep 19 '19 at 13:18

Jim

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This can work on a deeper pond, where what you are really doing is extracting heat from the ground by circulating the water from the deep parts. At 12" depth, it's going to freeze solid in any place with "real winter." – Ecnerwal Sep 19 '19 at 13:31

How can I heat a hole in my pond efficiently in the winter without using a pond heater?

3 Answers3