My ritchies came with 250 watt heaters but I changed them to 500 watt ones this winter. The 250 did the job but when it got down to -20 the water would freeze over in the bowl. Never solid to the bottom where it would break anything or freeze the lines but some times I would have to break ice with a hammer when it was -20 or colder. The 500 watt ones never allow any ice at all.
Do you have your waterers out in the open - I would think that would make a difference. And how many horses drink from it. With my 4 horses, I might need the 500 watt heater until I have more animals using it.
Too bad they get $400 for the wateres - otherwise I would have a few already.
If I remember correctly...some one posted last winter about using old ice chest (deep freezers), cutting a part of the top off and filling it with water, because of the isolation (sp) the water want freeze....i think...
I use the automatic waterers, LOVE them wouldn't use anything else... I am not sure of the watts? My old tank had a therestat that you could turn up in real cold weather, but the tank I have now has a internal thermestat that you can't change.
Forgot to add that it got down to -30 yesterday and no ice, we only get ice build up if there is a wind chill of -30 - -40 degree Celcius.