There is no secret to it. Just like in the summer warm up time and cool down time. However in winter instead of hosing the horse down they get blanketed with a cooler and then put their blanket back on. If you keep the blanketed appropriately for the temp in your area from the get go they do not get too bad. Had one in training all last winter not a single problem and no clipping. Just keep them blanketed.
Don't they get itchy when not rinsed off ? If the horse sweats a lot, surely its better to prevent the loss of salt by clipping rather than replacement in diet ? I do agree that many horses in light work are clipped needlessly, but for those that work hard, I can't see how they remain comfortable ?
My Traditional cob is so hairy that his winter coat takes 24 hrs to dry with a Thermatex on, in winter, tough fella, that he is, would, and has caught a chill. My WB X TB mare dries quickly being finer coated and she will not be clipped this winter, particularly as she'll be living out.
BTW, I'm not being pedantic, I'm really interested to know how you avoid clipping with the thick coated horses.
Miss H , Mentioned above, we use the Bucas rugs that are designed for turning a wet horse out in, the inner lining stays dry while the horse drys. They are very good.