My 28mm Warlord pike & shotte horse are 30ish mm to the ears, so yeah, if it'll let a figure in a hat and typical wargames base through, your doors should fit a horse.
I did an ECWish half timber & thatch barn just over a year ago, and the door is 35mm or so high, so it'll fit a led horse but not a mounted man. LAF thread on that one
here.