I understand what you want. I hope this pic. helps. The intake air that is coming in from under the house is 76*. There is a 200 mh cfm 25' away pushing air to my room. The exhaust fan is a 350cfm drawing the hot air out the roof of my room. Where are you going to get your fresh air from? If you are going to get your intake from the same place your exhausting into, you might find that to be a problem. As you can see my 250mh is 90* and thats with cooler air blowing over it . I hope this helps. Also I included pics of my air ducts . Both the room and light are cooled from the same plenum, thats behind the wall on the floor. I know a mh is not a hps, but I dont think there is much difference in heat. Watts is watts. And that is where the heat come from (I think).
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