In the basement, we have a temperature of 17 Celsius in summer time. On the 2nd floor it's about 28 Celsius. I thought of transporting the cool air to the 2nd floor, by attaching flexible tubes together and putting a fan every meter. The tube's diameter would be about 20cm.

I am sure this is only a bad idea, i don't know which downsides this idea could be and I am sure you guys now a better way.

  • Is the basement moldy? Jun 23, 2014 at 5:14
  • Do you have a forced-air system now? Two comments on your idea: 1) a fan every meter is overkill; one is enough and it doesn't really matter where it is (should just be based on minimizing sound from the motor, ease of access if it breaks). 2) when you force air into a room, the existing air has to have somewhere to be displaced to. Modern HVAC systems have a supply and same-sized return in (nearly) every room; some smaller rooms (eg, bathrooms) may rely on a bit of airflow though the gap at the bottom of the door and the door being not fully closed most of the time.
    – gregmac
    Jun 23, 2014 at 18:19
  • 1
    It sounds like your real problem is an insufficiently-insulated attic, which is causing the second floor to overheat due to solar gain heating it up and radiating that heat down through the ceiling. I would fix that instead, and then see how much it helps.
    – iLikeDirt
    Jun 25, 2014 at 15:11

1 Answer 1


I've had that idea before too... it seems very tempting to get "free" cooling by simply moving air from the cooler basement to the hot upper floors.

I've never tried it, but some problems with this idea might be:

  1. It takes energy to move air, which will turn into extra heat in the cold air. Since you have to raise the cold air several meters, you'll be pushing against natural convection. The temperature coming out of the top of the stack will be somewhat warmer than the temperature in your basement.
  2. Since the temperature difference between the hot and cold sides isn't that great (think about how cold the output of an air conditioner can be), you'll have to move a lot of air to make any sort of noticeable difference. This will make problem #1 worse - moving more air means more energy.
  3. Any air you remove from the basement will have to be replaced by air coming in from somewhere. This air will be warmer, and depending on your climate, may have significant humidity. When the warm air comes into the basement and cools off, its percent relative humidity increases. This process happens naturally all the time, but you'll be accelerating it with your fan. If you already have basement moisture problems, this will make them worse - and it might make moisture problems happen if you don't already have them.

Oh, and one other important thing just in case it applies to your particular situation: in the very unlikely event of a fire in your basement, this air duct could easily become a chimney that pipes hot combustion gases straight up to the upper floors. As those hot gases leave, fresh cold air will tend to rush in and feed the fire, making the fire worse. This is why building codes typically require firestop protection in basement ceilings around fire-prone areas (such as your furnace). Definitely don't do this if the inlet for your duct is near your furnace or any other possible source of fire!

  • 1) 4 of 2 Watt fans wan't produce so much heat, but why would the air would get warmer, when i push it 3 Meters high? I can imagine that it will become 1 degree warmer, but not 5 or 10? this would be ok 2) this makes sense 3) we are in germany, the airhumidity is in average 50% and our basement is much bigger than the rooms to cool. Final: Maybe i should give it a try. I was just afraid of any dangerous change... like pressure and so on. but you didnt mention anything like that. thanks! Jun 27, 2014 at 22:27
  • Sure, go ahead and give it a try - it's the only way of knowing for sure! Also note I've added one more warning (about fire risk) to my answer if it applies to you.
    – kgutwin
    Jun 29, 2014 at 0:35
  • I don't think your first point will be an issue at all, but the rest of the answer makes some great points.
    – Doresoom
    Oct 2, 2014 at 19:04

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