Re: Houseplants and oxygen levels in the home.

This is an interesting question. It's probably not practical to use houseplants 
to raise oxygen levels in homes for several reasons including low light levels 
in most homes, the low carbon dioxide levels in the air,  oxygen consumption by 
residents, and the typical ventilation rates in homes. Unless the house was 
hermetically sealed, any surplus oxygen produced via photosynthesis would leak 
out of the house so the oxygen concentration could not be maintained 
significantly above the level in the outside atmosphere. A hermetically sealed 
house would be impractical, expensive and potentially dangerous because gas 
stoves, gas furnaces, and cooking odors need venting.

Because the carbon dioxide concentration in the air is so much lower than the 
oxygen concentration, photosynthesizing plants can quickly deplete all the 
carbon dioxide in a tightly sealed space, as in a closed greenhouse in winter 
or a home. Therefore, ventilation or a carbon dioxide source is required to 
maintain photosynthesis.

To get an idea of the magnitudes involved, it is instructive to roughly 
calculate the amount of plant area required just to supply the oxygen 
requirements of one adult. Assume plant photosynthesis fixes 25 grams of dry 
matter per square meter of land area per day. This is a high outdoor rate. If 
that 25 grams is pure carbohydrate, it has a food value of 125 calories because 
carbohydrate contains 5 calories per gram. If you examine a food label, you 
will find that an adult typically consumes about 2000 calories per day, which 
is respired using oxygen back to carbon dioxide and water. Therefore, it would 
require roughly 16 square meters of land area covered with plants to provide 
the daily oxygen requirement of one adult. Sixteen square meters (176 square 
feet) is a large area relative to the area of an average house. I would guess 
that the photosynthesis rate of houseplants in a typical home might be at most 
about 5 grams per square meter per day so that would mean 80 square meters (880 
square feet) of plants per person just to provide the daily oxygen 
requirements. Based on these calculations, virtually all the floor space of an 
average family house would need to be covered by houseplants just to provide 
most of the daily oxygen requirements of the residents.