We still haven’t had snow since we made our bird bath heater to test it thoroughly, but we have had some low temperatures and frost.
As long as we keep an eye on the forecast, and turn the heater on early enough the night before we are due a frost, it works, the water is prevented from freezing. Our other bird bath freezes so we know it’s cold enough to do so.
The best thing is now it’s made and working the effort we need to put in is minimal – just remembering to turn it on from the workshop, which is close to the house, when a frost is forecast, easy! (and off in the morning) No need to wander down the garden with a jug of replacement water – for this bird bath anyway.