HPS is definately warmer, and should be vented out. Good ventilation is also required into the space (nice to have a carbon scrubber to keep dust, pet dander, and cooking smells out at this end), and good ventilation out of the space (again a carbon scrubber is a must) the filter on the intake will keep the more important one working longer. These are relatively cheap - check Amazon. I picked up a pair that came with Vivosun 4" inline fans - flip the carbon between batches (if necessary), and replace the carbon annually (can buy it at any aquarium store). If you live (and grow) in a cold environment, vent the filtered air back into the rest of the house - if it smells like pot, time to change the carbon.