At the barn my horse is kept there is a few bathrooms and a tackroom with a sink, so hot water is everywhere.
I'll usually fill a bucked up with hot, not warm but hot water from the tackroom. It's freezing where I am located, and even colder at nights which is generally the time I can see my horse. There and two seperate barns, one with the indoor arena and tack room in it, and a seperate one in which my horse is kept.
And while all I have to do is open the door of the tack room barn, walk 7 feet in the cold to the barn where my horses stall is, the hot water is always to a perfect warm by the time I reach my horses stall due to the cold.
I'd say if you can fill up the bucket with the warm water from a sink in your house, assuming it's not a super long walk from your house to the barn.