Re: what house plant produces the most oxygen?

I'm not aware that any scientists have experimentally determined which of the 
many hundreds of houseplant species produces the most oxygen. In general, a 
larger or faster-growing houseplant will produce more oxygen than a smaller or 
slower growing one. Also, with two identical houseplants, the one receiving 
more light will likely produce more oxygen assuming the plants receive adequate 
levels of water, mineral nutrients and temperature. Houseplant growth is often 
limited by low light. 

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. 

Also remember that plants use oxygen gas and give off carbon dioxide gas in the 
dark when there is no 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 100 calories because 
carbohydrate contains 4 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 20 square meters of land area covered with plants to provide 
the daily oxygen requirement of one adult at 25 grams of dry matter per square 
meter of land area per day.. Twenty square meters (220 square feet) is a large 
area relative to the area of an average house. Most homes do not have an area 
of 220 square feet occupied by houseplants. 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 100 square meters (1100 
square feet) of houseplants per person just to provide the daily oxygen 
requirements of one person. Based on these calculations, more than  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.