Venting down

Hey guys, thanks for the help so far. Anyway. I am just starting my setup, everything is working great, other than my venting situation. I really can't vent outside. I am thinking of venting down, into my crawl space. It is really cool down there, and should work great. What I plan on doing is running some dryer ducting from the top of my room into the floor and down into the crawlspace with an inline fan to pull the air down. I know heat rises, and it is always easier to vent up, but you think this should work ok? Cheers guys.

My room is only 4X4X8, I will have only 3 plants flowering at most, 400HPS for flowering. It is a cool room, so I am not concerned about the temps...

Venting into lower crawl spaces is good too. You dont have to have the duct going up high in your room. Maybe arrange it so a fan is blowing over the top of your plants to push away the radiant heat. Then have your out vent on the opposite side of the fan, that way the out vent catches the radiant heat.