Pond air pump to keep from freezing

[Pond skipper]

Hi all, trying to figure out how big an air pump I will need to keep an air exchange hole open all winter here in central Ontario, I’ve been using a really large one a friend gave me but I think it’s overkill. It’s kind of industrial size from a large pond and used a lot of electricity and is noisy. I’m wondering how to know what size (specifications) I could get away with. The pond is not really big, I think it’s about 1250 gallons
(20’ x 6’ x 1.5’ deep) our temperatures can get pretty cold but pond doesn’t freeze to bottom. My goldfish survive just fine