Having all of those sliding glass doors will certainly help...a little. But, the warm moist air will naturally want to rise straight up. So, unless there is a fan that can direct the warm moist air sideways, toward the sliding glass door opening, their benefit will be minimal. In other words, you will need an exhaust fan large enough to move a lot of air laterally so the warm moist air won't rise and get "trapped" in the ceiling area. Having a fan blowing across the top of the tub, while you are using it, may not be very pleasant. Also, it could take a rather large fan in the ceiling to remove all of that moisture if you chose to go that route. I don't know if you have ever noticed...when you take a long hot shower, the bathroom exhaust fan never actually removes all of the moisture. There is condensation on the mirror, walls and ceiling.
Here is something I wrote for another forum about this exact issue.
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Interesting question. It is logical to think that an exhaust fan (EF) will remove humidity, and to some degree, it will. But, unfortunately, EF’s are not usually intended for humidity control. They are typically used to contain and remove odor, smoke, air born particulates, air born bacteria, etc., as well as achieving specific room pressurization criteria.
If you were to use an EF for humidity control, you will need some means of replacing the air that you are exhausting. This will most likely come from outside the building. So, if it is warm and humid outside, you will be bringing in warm humid air to replace the humid air that you are trying to get rid of. Not very practical and somewhat counter-productive. Also, if it is cold outside, you will be bringing in that cold air while exhausting the humid air. Again, not very practical. Plus, this introduction of outside air is unfiltered and unconditioned, causing your heating/air conditioning system to work harder. The only time this would be feasible would be during ideal outside air conditions, which does not happen often enough to make it worthwhile. Another option would be to bring the outside air in through your heating/air conditioning system first. This way the outside air would be filtered and conditioned before it gets to your room. But, this can be costly to install and will certainly cause your heating/air conditioning system to work harder. Perhaps even requiring a completely different heating/air conditioning system to handle the added load requirement.
Controlling humidity within a building is usually accomplished by a heating/air conditioning system alone…no exhaust fans. Go to a public indoor pool and you will likely notice there are no exhaust fans. Their elaborate heating/air conditioning system handles the humidity control. But, a system designed for this type of control is more elaborate than the average home system. It is also much more costly to install and operate. In most cases, not very practical.
I would suggest you go to your local hardware store and purchase a couple of dehumidifiers. Start off with 1 or 2 and see how it does, and add more if necessary.
Hope this helped.
