I have never had any problems going up and down stairs all day. In fact, when I sense I am overloading from one task or activity, I usually go to a different floor of my house.

Heat can be a bit more of a struggle but I have learned to tolerate heat by being more consistent in my speed of activity. No racing around in the heat. Walking at a casual pace works best for me.

But this is my experience, your mileage may vary.