This sounds to me like a perfect application for a 1-Wire network.
You are probably looking at a bigger network that you could reliably work with the kernel based driver but with a DS9490R USB host adapter or an I2C based host adapter such as my RPI2 (http://www.sheepwalkelectronics.co.uk/RPI2.shtml
) or AB Electronics' 1-Wire Pi (http://www.abelectronics.co.uk/products ... /1-Wire-Pi
) you could then build a network with temperature and humidity sensors as well as output modules to switch relays to control fans or vents. Sensors and modules for this are available from various suppliers including myself and HomeChip in the UK, or Hobby Boards in the US.
You would probably run it all using the OWFS software which allows you to write your control software in your choice of languages including perl, python or php.