Joe has some good advice. Insulated ducting and hoods. I am currently looking into this as I battle high temps in a tent. The ducting also heats up the room the tent is in.

They sell special covers for the hoods or you can just get the sheet insulation and cut it to size.
GetThisOrDie Reviewed by GetThisOrDie on . Some pics of my setup. Could use a lil constructive criticism Ok here it is. My flowering room is 11'x9'x7'. I have 4x 600w HPS running for flower and 1x 1000w for early veg after they come out the ez-clone. I have a gen-1 propane co2 burner with 4 burners, a dehumidifier, the can fan 100 combo which is nothing short of a giant ass carbon filter with their 8" HO inline fan. That is all connected with ducting and running through the air cooled reflectors. And running the whole show is the Harvest Master Climate Pro. "let me do all the work" it says lol. Rating: 5