Yes, the idea i had was so saturate the inside of the lower chamber/grow area with so much fresh air that it pumped it up by shear volume. But the pipe idea sounds intriguing. If I put a tube over the fan vent at the base of the fans, then I could pump it up and flow it down around the plants in a more direct manner. This may look weird in the grow area, pipes sticking up from the floor. I was trying to keep the air coming in, separate from the HOT AIR going out. allowing the heat to draw the cooler air up (Co2) around the plants. Also I do not want to run the fans at full bore. I have tested 4 fans on one adapter set at a lower operating voltage 7v\dc, which would allow me to control the flow into the chamber. At £1.50 a fan, maybe sticking the fans on near to full operating speed may be less of a hassle with the set up so that the air flow is more progressive. My earlier grows failed due to a lack of ventilation and I want to get it right this time.
re-edit May be if I have floor fans and a couple of side fans with up/pipes to make sure of maximum Co2/air flow.
I have stopped growing for a while and I am in the process of sorting out some kit to get going again. I will be using a large wardrobe/closet on 6" legs. I have been thinking about adding active ventilation to the grow by placing 4/5 PC fans under the grow cabinet (holes between 10lt pots x 12) to pump in plenty of Co2. 
