Ok I have been trying with limited success to have a birdbath that lasts [stays liquid] for the entire winter. I’m am not familiar with various ways to keep the water warm during the winter, but I am familiar with keeping it moving with a small fishtank air bubbler. However, my problem comes in when it is -20 and not matter how much movement you have the water freezes anyway.
This is where I get to wondering about volume and movement. We havea local park with a duck pond, they keep bubblers in that all year long, and in the winter the water doesn’t freeze. The outskirts of the pond will freeze, and the areas not with a bubbler will freeze, but usually a 10’ diameter circle around where the bubbler is stays liquid even on the coldest of days.
Why doesn’t my birdbath do that? I have a granite birdbath roughly 24" in diameter, with 6 inches of water in the center leveling up to about 3 inches on the sides. I have the bubbler in the middle and it keeps the water quite liquid most nights… But as I look out at it right now, I see it is completely frozen over and the little bubbler is bubbling away under the ice.
Could I heat the water some how? If so how should I do it?
I think the volume does affect it, since the change in temperature is related to the grams based on the specific heat capacity equation (specific heat = energy / (change in temperature x grams). Since water has such a high heat capacity, it resists changes in the temperature more readily than most substances (which is why we turn the sprinklers on, at least down south, before a freeze - ice-covered plants stay warmer than those exposed to the cold air).
I guess you could add anti-freeze, but that would kill the birds. Maybe there’s another additive you could add that would be safe. I’d say salt, but I think you need a ton of it to affect the freezing point (that’s another equation that lets you calculate it, freezing point change = molality x freezing constant).
Water is at its highest density at 4 deg C, around 39 deg F. The bubbler works by dragging the warmer water at the bottom of the pond to the top via friction. Your birdbath is too shallow to have any kind of temperature gradient. The only way to keep a birdbath from freezing in cold weather is to heat it.
