Condensation question

[Keys]

A tenant walks into the bathroom. There is an extraction fan which they choose to leave off. There are windows and doors which they choose to leave closed. The tenant takes a shower.

Question:

Does the air pressure in the bathroom increase:

Please supply a reason for your answer.

[Davo36]

Not really, heat would make the air expand a bit, but it would escape under the door.

Unless the bathroom is hermetically sealed that is.

[sidinz]

Does the air pressure in the bathroom increase:

Please supply a reason for your answer.

Do you mean due to the addition of water molecules to the air mixture?

[Bob Kane]

I don't think the air pressure would increase.
The bathroom is not sealed therefore any increase in pressure would be released immediately outside.
Equally, any decrease in pressure and the outside air would flow in.

[Bob Kane]

I'm surprised that our resident expert-on-all-things hasn't contributed their opinion.

[Viking]

Depends if the fan is off or on. Fans don't stop condensation they just move the air around. So if the air is warm and full of moisture but the ceiling/walls are cold the moisture will still condense on the cold spots.

Install a shower dome. No more problems.

http://curtaincleaners.co.nz/whys-and-all-about-curtains/about-mouldy-rooms-and-mould/

http://curtaincleaners.co.nz/whys-and-all-about-curtains/what-about-water-on-the-windows/

[teamchase]

How is the question relevant to adequate ventilation? Air pressure vs air flow/changes
A: Whether the pressure increases or decreases would depend on the weather patterns moving over the country at the time and how many hours/days at a time they chose to stay confined in the shower waiting for the barometer to adjust accordingly.

[Perry]

Question: Does the air pressure in the bathroom increase? Please supply a reason for your answer.

Not really, heat would make the air expand a bit, but it would escape under the door.

Agree with David.

[Learning]

We did this in physics one year but I can't remember exactly. Along the lines of a rapid change in pressure while the shower is running but would dissipate almost immediately as soon as it's turned off. It's easily demonstrated provided the shower's powerful enough. Ever notice how the shower curtain attacks your legs during a hot shower? Something to do with the force of the water displacing the air causing a pressure drop and then as the hot air rises that increases the pressure change, low pressure in the shower, higher pressure over the top of the curtain and behind it and pulls the curtain in. I couldn't say it the overall room pressure would change though.

[Perry]

I suspect 'pressure change' is a bit of a red herring or misnomer. Seems to me to be more like some convection and a bit of fluid dynamics.

Still wondering how this bears upon some aspect of residential tenancy, though.

[sidinz]

I suspect 'pressure change' is a bit of a red herring or misnomer. Seems to me to be more like some convection and a bit of fluid dynamics.

I dunno. If the bathroom were sealed, all that water vapour would be adding to the mass of gases in the air, wouldn't it? (At least until it was saturated and condensation occurred.)

[Perry]

If it were sealed . . .

[Learning]

If it were sealed . . .

Sealed and humidity increasing then of course the pressure will increase. Adding mass to a sealed container, like filling a gas bottle.

But in a real world situation the pressure would equalize through gaps and cracks almost immediately.

[Wayne]

If the bathroom was sealed and the shower drain was blocked the pressure would increase due to the decrease in space for the given volume of air.
After all you are introducing additional water taking up space.
But this would never happen.

As for the shower curtain clinging to your body - this is due solely to the heated air (heated by the water - steam) rising and trying to draw cooler air in. Move the curtain slightly to break the seal and the cling stops.