This bath exhaust fan ,which is thermostatically controlled , pulls hot air from the peak of the gh roof and blows it underground thru 4 inch perforated pvc pipe buried about 12 " down or just below rototiller depth, each gh has 65 ft of this , it a good way of using the free heat of the sun, to expedite soil warming, of coarse it only works when the sun is out, which isnt to often so far this year...
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