Chris (this is for you Saverain also):
Plants do not only emit Oxygen they also emit CO2. In fact, they emit oxygen only during the day time if there is light around them, but they emit CO2 24 hours a day. In the overall sum of things - they emit more oxygen than CO2, but during the night they emit only CO2 and no oxygen, therefore - during night time - which is the time people spend mostly inside their homes - many plants in the house can only serve to increase levels of CO2 and decrease oxygen. For this reason - it's well known that if you sleep in the same room with many plants it is always advised to make sure that there is a window open, or the oxygen levels might become dangerously low.

Saverain,
Once again, plants in the house - which does not allow the penetration of sun, like a green house does, and that also has to allow a lot of fresh air circulation (which is another thing that a green house and a residential differ in) - will not cause any kind of felt evaporation and condensation from the plants.
If ENS sufferers want more oxygen - they can open a window - and by the way why do you think that we need more oxygen in the air we breath anyway?
And if ENS patients what more humidity - one small humidifier in the corner will raise the level of humidity more than a hundred plants in your house, which will need watering, caring, pruning, and invite insects into your house.

Besides - you should know that humidity is a double sword edge. If an ENS sufferer were to live in a real green house he/she most likely would develop asthma in less than a year, because humidity breeds mold, and thus with a poor nasal defense system any way in ENS - expose ENS sufferers to asthma, chronic rhinitis, allergic reactions etc'.

Happy gardening.