I've tried all major vent systems,The latest being charcoal(very large and expensive) and does not work to my standards at all. Purchased new home on small lot. But it has a septic tank and large field 300'.think of running 2 or 3 6'' vent pipes underground to second tank which will blow air in field.A friend built a large pit ,filled with washed rock,3'' of straw, 3'' of black soil, green sod, run his 3 underground vents for a total cost of under$1200, said it works great!!! I want to grow for next few years. Two biggest problem's are electrical cost & ventilation.ANY thoughts on above or better systems. Thanks