Author Options:

Can the change in atmospheric pressure inside the house automatically drive a mounted exhaust fan ? Answered

I used to live in this house some 3 years ago, it had exhaust fans in every washroom , now if i opened up the doors of all the washrooms closed the windows and disconnected the exhausts from electricity and would just move any door in the house slightly it would cause the exhaust fans to go wild and spin like jets !

Now i need to know what principal is involved here ? or was it really happening because of what i hypothesized ? Does it happen in your house too ? 



Heat rises and in the summer, the attic is 140 degrees. I suspect the hot attic air would rise up and out your roof vent turbines and would draw air up from the living space through the vent fans. This would help cool the house in summer, but would be a lot of lost heat in the winter time. Do not block the vents in winter. My brother did that and then someone turned on the vent .... not knowing duct tape was across the fan. After many hours of overheating, the fan finally caught fire and burnt his trailer down. Luckily nobody was hurt in the fire.

trust me i have very good experiences with it.

The mechanism behind it is super easy when you open or close the door you push air in either direction and as you said the pressure increase because of it and air flow from high pressure to low pressure and thus you generate a wind stream which needs a way to escape and since windows are closed the only escape is the exhaust fans hole and else is done by the fan.It just starts to rotate as a wind mill.

My window cooler generates nice pressure difference so by adjusting the doors and windows I adjust the wind flow to spot just where i sit ahh..! 6th grade science can be so easy.


4 years ago

A lot of the newer fans have dampers in them to prevent unwanted air flow. In the winter time a huge amount of heat can go up those fan ports. Its like having an open window. You can get a weatherization test done and one of the things they do is put a big fan in the door with a seal around it so it creates a vacuum in the house. Then you can find all those areas that air is infiltrating in from.

One of the reasons tornadoes do so much damage is the extreme drop in air pressure they create. A house can blow open from the inside air trying to get out and then the tornado winds shred what ever it can get into once it has a starting point.

Yes. When you open a door into a room you are pushing the air in and increasing the air pressure in the room. That air pressure wants to go somewhere to equal out. So any free spinning fan between the room and the outside will spin as the air pushes past it. Likewise if that door opened outward into a hall it would pull some air out of the room causing air to be sucked in through that fan and spin the fan.

Run a test. Go into a bedroom with the windows closed. Now try slamming the door. Now open the windows and slam the door again. Notice the difference? With the window open the door shuts faster and harder. With it shut the door is fighting air pressure a bit. it's basically fanning air out of the room and there is no easy air supply to fill in the void being created. So air is being sucked in from where ever it can come from. Be it around the edges of the door, leaks in the window or what not.