That'll probably keep the ice off the pond in a small area, but it all depends on how long of an extension cord you need.

That 1500 Watt one is the floating tank heater that your local farm feed stores carry. I don't know what temp it turns on at - there is no external on/off switch, nor an adjustable theremostat.

www.hoosierpondpros.com

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3/4 to 1 1/4 ac pond LMB, SMB, PS, BG, RES, CC, YP, Bardello BG, (RBT & Blue Tilapia - seasonal).