Good feed in adequate quantities will protect the healthy horse from cold weather with a layer of fat. Well-fed horses will have short hair, even in winter.
Design your farm/barn system so your horses can get lots of exercise, through either working or access to a paddock.. Standing for days on end in a tie stall or box stall is unhealthy for a horse. Horses are healthier in winter when housed in a cold barn; then they are not shocked when they are moved from a warm barn to a cold paddock.
To avoid respiratory problems, well-ventilated buildings are best for horses—cold/dry, rather than warm/damp. If you bring hot sweaty horses into a cold barn, blanket them until they are dry.
Standing stalls work well for working horses, and take much less space than box stalls. Horses are easily harnessed and unharnessed since they are already tied. Standing stalls are easier to clean and use less bedding than box stalls.