I Does Humidity "Disperse" and "Even Out" in Enclosed Space?

[kyphysics]

I have a dehumidifier (just one) that is placed indoors in the house in a "central" location (maybe not perfectly center, but close). Obviously, the local humidity around the machine will get sucked out of the air and turn to water. But, would the humidity in a different part of the house be affected? As in, would less moisture in the air in the center of the house mean that the higher moisture in the air in other parts start to "even" out and "fill in" the less moisture area in the center again?

Or, would you have to physically carry the dehumidifier (mine is quite large) and plug it in and run it in different parts of a house? The latter seems a pain in the butt, but I'd be willing to do it if it helped.

Just thought maybe you wouldn't need to, as humidity may "even out" in a room/house/enclosed space on its own from some physical laws. Thanks!

 

[Lnewqban]

When a vapor-pressure differential exists, water vapor will move toward the lower pressure independently of air movement.
That force drives vapor even through building walls, if not containing a suitable barrier to it.

Please, see:
https://en.m.wikipedia.org/wiki/Humidity

Humidity contained in the air filling your house, will naturally find the dehumidifier.
The vapor dissolved in the surrounding outdoor air, if it contains more water than indoor's, will "feel" the urge to infiltrate itself into your house.

 

[Chestermiller]

Pure diffusion even in air is a relatively slow process, but this process is enhanced substantially by the home ventilation system, which provides convective circulation movement of high humidity air into proximity with the dehumidifier. The humidifier also has its own blower to help with this circulation. Still, you can expect lower humidity near the dehumidifier than further away.

 

[jrmichler]

I also have a portable dehumidifier somewhat centrally located in the utility room. It adequately controls humidity in the master bedroom, which is down the hall, through the kitchen, and through the living room. We only need to remember to leave the utility room door open when running it.

I originally had a central whole house dehumidifier, but replaced it after it failed twice in a little over five years. The first failure was replaced under warranty, but the labor cost to remove and replace it was considerably greater than the cost of a portable dehumidifier. And modern portable dehumidifiers are efficient and quiet enough that there is no advantage to a whole house unit.

 

[Keith_McClary]

Pure diffusion even in air is a relatively slow process, but this process is enhanced substantially by the home ventilation system

Some older buildings with hot water or steam heat don't have a ventilation system (other than windows). Newer ones may have heat exchanger systems to bring in fresh air. Note that dry air is more dense than humid air, so it will tend to pool at floor level. Fans may help to distribute it.

 

[kyphysics]

When a vapor-pressure differential exists, water vapor will move toward the lower pressure independently of air movement.
That force drives vapor even through building walls, if not containing a suitable barrier to it.

Humidity contained in the air filling your house, will naturally find the dehumidifier.

Quite helpful, thank you!

The vapor dissolved in the surrounding outdoor air, if it contains more water than indoor's, will "feel" the urge to infiltrate itself into your house.

This part sounds logical, but still surprised me, given the barrier of wood, brick, etc. of homes. Kind of amazing.

 

[kyphysics]

Note that dry air is more dense than humid air, so it will tend to pool at floor level. Fans may help to distribute it.

I could be mixing things up, but I thought it was the opposite. Non-science person here (despite my screen name), but I've been reading up on COVID in past months.

One thing I swore I read (although, again, I could be mistaken) was that COVID was less transmissible in humid air - all other things being equal. That's because the air is "heavier" (what I'm interpreting as your use of "dense") and when people speak and spew water droplets from their mouth (including COVID), it more quickly falls to the ground (thus not reaching someone else's nostrils). On the other hand, with less humid air, the virus can get aerosolized and float around in it longer.

...or so I thought...Was this just incorrect?

 

[kyphysics]

I use a Danby Energy Star 70-pint dehumidifier. Researched these using Consumer Reports and Amazon/Home Depot reviews. Have had it for maybe 1.5 years and it's still working well. No leaks or slow down of things.

Often, I'll see reviews say the thing conked out after a few months. Not mine.

 

[jim mcnamara]

This is kind of a fun, site you can mess with various properties of air like temperature and see what happens to density. @Keith_McClary made me wonder...
https://www.omnicalculator.com/physics/air-density