They help heat it yes, every animal (and human) puts off some heat, that coupled with many other factors make for a energy free green house. As for oxygen even if it was as sealed as a ziplock bag...(its not though haha) its big enough and we go in enough that it would take days to run out, (and thats without plants). The rabbits are housed under the shelves me set out plants on..

A post on this is on the list but might wait till winter so all can see it in action.