Most well pits around here have a insulated over sized box covering them with the pressure tank and pump in the same box. That's for shallow wells. Then you can put a heat lamp or dairy heater on a thermostat. If insulated well you can get by with a light bulb. Not LED. You can push water better than pull. And like Lugnut said 36" min but 48" is preferred for the waterline. Now there is rural water and deep wells that go directly into the building with no outside box or building.