If there is stuff that thrives under snow think how much more the wee-beasties will bloom at a tropical 60°F and if re-circulating household air those are YOUR wee-beasties from microscopic skin flakes, cough and sneezes, pets, cooking and whatever was in the home before you arrived. If you decide to provide for some energy savings by using earth temperatures make the system scrubbable or floodable using non-porous plastics...