I also climb stairs in a tall building as my main workouts.
My building has 20 flights (260 feet) of elevation gain per lap, and I can get down the elevators in 35-45 seconds. I usually only go up, and take the elevators down, doing laps ( with weighted pack) for up to 2-4 hrs some days. I can get my HR to AeT pretty easily if I choose.
……so I also would like to know if this is adequate without adding running into the program. ( climbing stairs are easier on my aging knees!)