About ten years ago we pulled our irrigation well. It had two tubes. One ten inch with a quarter mile of run to the north. One twelve inch with three quarters of mile run to the west. All buried more than four feet. Probably more like six to eight feet. I would like to build a winter greenhouse and I was wondering about the feasibility of pulling air through the ten inch pipe. I think the soil temp is around 55°. Do you think it is a good idea? Will it be efficient enough to justify me digging the hole to tie into it? How large of fans would you use? I have twelve inch bin fans. How do you set them on a thermostat. Do I want to pipe it directly into the building or pass through a heat exchanger. I can't spend a lot of money on this project but do have most of the materials on hand. Including lumber, valves, irigation fittings, and insulation bricks. I have electricity and water close at hand. I know this is not your usual installation but I see an opportunity. Its in the right spot and the price is right. I also thinking of burying a 500 gallon tank to act as a water thermal mass reservoir.