How to run longer in the winter?

How long of pipes do i need to run to heat the cold winter air up to ground temp.?

• I want to run a bucnh of 4 inch pipe underground and then out to daylight. But i don't know how far I need to run them to allow enough time for the cold winter air to warm up to ground temp.

• Answer:

  It depends on: 1) The thermal conductivity of the pipe (metal will heat the air faster/more than plastic pipe), 2) How fast you move the air through the pipe, 3) Whether you bury the pipe deep enough (below the frost line, plus more) RE: Your Additional Details: Plastic pipe is such a poor conductor of heat, that this would be quite ineffective. You would probably get as much temperature rise just from running the fan to circulate the air inside the building. Better yet, run a small electrical heater that wouldn't use any more watts (cost) than the furnace fan. By the way, I notice that my cold water faucet temperature is quite cold during 20 degree weather. The incoming water lines are below the frost point, yet the cold water temperature feels about 40 deg F. So underground temperatures apparently are not very warm in the winter anyway.