Is my landlord right about air circulation & mold prevention?

July 23, 2012 1:09 PM

Landlord is very insistent that if we don't open our bathroom window a particular way, the air will not circulate and the mold will take over and also there will be doom. Does he know what he's talking about?

Our bathroom: a small room with no ventilation fan and a single average-sized double-hung window with a thin plastic shade. After showers we generally raise the shade, open the top part of the window, and leave the (frosted) bottom part of the window closed, which I've always thought allowed us the privacy to be naked in our bathroom post-shower while still providing enough ventilation for the bathroom to dry out. The landlord insists that we absolutely must open both the top and bottom parts of the window, otherwise the air won't circulate. I'm not entirely sure that a) that's how air circulation actually works or b) the air needs to "circulate" in order to prevent mold.

Full disclosure: I'm also a little annoyed that following his instructions means that anyone walking by the bathroom window will be able to clearly see us in the bathroom, and I really don't want to have to put clothes on immediately post-shower or try to find somewhere else besides the bathroom in our tiny apartment to get ready. But if he's right I'm willing to make the sacrifice, because there is a minor shower scum/mold? problem that we keep under control with scrubbing, and I don't want it to get worse.

So, AskMe physicists and bathroom mold experts, is our landlord right? Will opening both parts of the window help the air circulate and thus better prevent mold?

posted by rhiannonstone to home & garden (24 answers total)

This sounds like he envisions that the air will enter through one open section of window, circulate through the bathroom, and then obediently exit through the other open section of window. This is a silly thing to believe unless there are a series of carefully placed fans producing the necessary air currents. An easier way to ventilate the bathroom would be to open the part of the window you prefer having open and then open the bathroom door immediately after showering.
posted by elizardbits at 1:15 PM on July 23, 2012 [8 favorites]

My bathroom has no window and no mold. (I also don't have a fan in there.) Either I shower with the door open (I live alone) or point a fan into the room for few minutes post-shower.

Unless you're completely sealing off your bathroom with warm, moist air in it--and it sounds like you're not doing this--you oughta be fine with regards to the mold situation. So the way I see it, you've got three options:

1) Open the window per your landlord's instructions and let all of your neighbors see your naked bits.

2) Open the window like you normally do and lie to the landlord. Your bathroom really should be fine, but obviously if you start seeing any moldy spots, bleach them immediately and change up your routine.

3) Tell the landlord that if he's concerned about mold in the bathroom, he needs to install an exhaust fan. If you're paying for your own heat, explain that it's completely unreasonable to expect you to leave a window open during the winter.
posted by phunniemee at 1:16 PM on July 23, 2012 [15 favorites]

I'm unclear on why you feel the need to either prove or disprove his claim. It's your bathroom, you can open the window any way you see fit.
posted by odinsdream at 1:18 PM on July 23, 2012 [7 favorites]

Does your landlord live on the premises? If not, who cares? Just don't listen and do as you see fit.

Does your bathroom have a mold problem? If so, I can see your landlord's concern. I don't think he's right, and even if he were he's being invasive. But I can see how he'd make some kind of illogical claim to deflect from the idea that it's his responsibility to provide proper ventilation or otherwise deal with the mold problem in a more hands-on way. Because bottom line, if there's a mold problem, having the window open a couple more inches is probably not going to be a magical quick fix.
posted by Sara C. at 1:23 PM on July 23, 2012 [2 favorites]

I think elizardbits has it pictured properly.

Could you open the window all the way after you've left the bathroom and can also leave the door open? That would likely go far to keep mould from forming.
posted by batmonkey at 1:27 PM on July 23, 2012 [3 favorites]

I came in to say what elizardbits said.

Shower scum/mold is to be expected (even if there were a ventilation fan in there, that type of mold would still form) and can be scrubbed off.

Mildew on the walls/ceiling is not great and can be avoided (as others have said) by opening the top bit of the window and leaving the bathroom door open after showering.

If your landlord is the type to swing by and check your bathroom window's configuration status, get what's called a dual window fan and stick it in the upper part of the window, and tell him you've done so. One fan blows in, one fan blows out, ostensibly circulating the air. Disclaimer: I don't think these work that well, but at least this would satisfy your landlord and be congruent with his logic.
posted by Specklet at 1:40 PM on July 23, 2012

If your landlord is the type to swing by and check your bathroom window's configuration status, get what's called a dual window fan and stick it in the upper part of the window, and tell him you've done so.

Actually, if your landlord is the type to swing by and check your bathroom window's configuration status, your landlord has too much time on his hands and ought to just install a proper fan. Elizardbits is correct about the air circulation.

I would find instructions from my landlord that would allow a direct line of sight onto Bathroom Nakedness to be troubling.
posted by ambrosia at 1:46 PM on July 23, 2012 [9 favorites]

It seems to me that your landlord wants you to set up a convection current in your window, with the idea being that hot wet air escapes from the top window and, in doing so, pulls cold dryer air at the bottom. No doubt better informed Mefites will correct me, but I believe that this is how traditional sash windows in the UK are supposed to work.
posted by prentiz at 2:09 PM on July 23, 2012 [4 favorites]

Unless you're renting a room in a house you share with the landlord, tell him to take a hike, it's none of his business how you open the windows in your home.
posted by easily confused at 2:30 PM on July 23, 2012

Does the landlord envision that with only one part of the window open, the air on both sides of the window just sits there, with no movement at all? This is not how fluids (like air) behave. But it's obvious that the air is not headed into the bathroom and somehow getting trapped there, or the bathroom would eventually explode (or at best you'd get back to the situation where air was just sitting there, not moving, which we already said was impossible). Ergo, when the top part of the window is open, air moves through the window in both directions, thereby circulating. The same argument will show you that the air in fact moves all over the room.
posted by ubiquity at 2:31 PM on July 23, 2012

Just to chime in again: sometimes it IS your landlord's business how you open your windows: there could be a mold clause in your rental agreement in which you promise to ventilate the bathroom in a particular way after showering. (I know this because we have one.) Maybe check you rental agreement before making a stand.

And prentiz has a point: double-hung windows do indeed allow for better air circulation. But. If your bathroom window is the size I'm imagining it to be (i.e. about 24" x 36"), the openings are not going to be large enough to get any significant convection airflow going.
posted by Specklet at 2:37 PM on July 23, 2012 [4 favorites]

Just to chime in again: sometimes it IS your landlord's business how you open your windows: there could be a mold clause in your rental agreement in which you promise to ventilate the bathroom in a particular way after showering. (I know this because we have one.) Maybe check you rental agreement before making a stand.

I have the same thing. By my lease agreement, my apartment is supposed to be ventilated daily to prevent mold and I have to report any mold to my property management immediately or I get dinged for abatement.
posted by LionIndex at 2:42 PM on July 23, 2012

My suggestions (similar to above): shower/bathe with the door open as well as the top part of your window and open the bottom part of the window when you're all done with getting dressed, etc. If you can't shower/bathe with the door open (privacy concerns?), at least leave it open after you're done in the bathroom.

Both Hunter and Honeywell have twin window fans. Here's a link to one at Walmart so you can see what I'm talking about. Here's a different one. They can fit either up-and-down or side-ways depending on how your window is set-up.

I've had a couple of the Hunter brand fans for three or four years now and they're still going strong.
posted by deborah at 2:52 PM on July 23, 2012

The landlord does live on the premises for most of the year, and while I don't think there's a particular clause in our lease about the bathroom, local rental laws would definitely allow him to hold us liable for property damage if our negligence (to properly ventilate the bathroom) led to a mold problem. Unfortunately the way this building is designed I'm afraid that there's always going to be a minor, perfectly normal mold/scum problem, and that he will always use that to "prove" that we need to follow his instructions.

However, I hadn't thought of the idea of a window fan, and I like it a lot. That'll look proactive to him, and, since a fan will undeniably circulate the air, hopefully eliminate the "need" to open the top part of the window. (That is, assuming we can find somewhere to plug it in and our sad outdated electrical system can actually handle it...)
posted by rhiannonstone at 3:00 PM on July 23, 2012

Indeed, it sounds like you have sash windows. Ask MetaFilter has discussed them before.

Wikipedia says: "A significant advantage of sash windows is that they provide efficient cooling of interiors during warm weather. Opening both the top and bottom of a sash window by equal amounts allows warm air at the top of the room to escape, thus drawing relatively cool air from outside into the room through the bottom opening."

So your landlord isn't crazy.
posted by qxntpqbbbqxl at 3:43 PM on July 23, 2012 [2 favorites]

If the window is positioned on the shower wall it might not be such a great idea to use an electric fan (a PITA to extension cord the thing, getting electrocuted, etc.). Personally, I'd opt for top of window cracked + open door.
posted by mcbeth at 3:44 PM on July 23, 2012 [1 favorite]

Just remember - when you are scrubbing the mould - DO NOT USE BLEACH - Bleach only well.... bleaches the mould. It is still alive. Instead - use vinegar.


posted by insomniax at 4:42 PM on July 23, 2012

Posted too soon

http://www.mould.com.au/mythsaboutmould.htm
posted by insomniax at 4:43 PM on July 23, 2012

High school, blistering hot day in June. 95F+, etc., and no AC in the school. We're sweating our butts off all day and walk into Physics to immediately be greeted by a rush of cool air and everyone screaming to hurry and shut the door. The professor opened the bottom windows before going home the previous night, to let cool air in, and then shut them that morning and opened the top ones to let heat out.

That I can vouch for. It was awesome, but the windows were probably 10 feet high, with "sashes" at the top and bottom for just such a thing (shame no one else knew about it!). Whether the same can be accomplished with your comparatively tiny window is a different story entirely, especially with both open at once, and in a room with very little air capacity to serve as a reservoir of any kind. I doubt it.
posted by jwells at 4:51 PM on July 23, 2012

You should get some very light airy but opaque bathroom curtains so you can leave it open and not have people see you. I know they exist because my mother has them.
posted by meepmeow at 7:25 PM on July 23, 2012

I was a landlord.

Mini-blinds allow air to circulate while not revealing you naked self. Angle them correctly for maximum privacy.

Tenants - 3 young women - kept the window shut despite my request that they keep it open (safe neighborhood, safety latch on window). The mold was nasty. Open the window in summer, probably doesn't matter which half.
posted by Mom at 9:12 PM on July 23, 2012

That is exactly how you're supposed to use double-hung windows to get air circulation (even with windows that aren't 10 feet high it's noticeably more effective). And wanting good air circulation to get the moisture out of the bathroom before it soaks into the mildew-able objects seems utterly reasonable to me. I don't think your landlord is crazy or unreasonable.

What about opening the window after you're done being naked? That is: shower with just the top open, get ready etc, then once you're clothed, open the bottom as well to finish airing out the bathroom. This assumes that showering isn't the last thing you do before leaving the house, I guess.

On the other hand, leaving the bathroom door open and only the top of the window open is probably just as effective (since there'll be some air current across the room then).

You can get tiny springloaded curtain rods that would allow you to put some light curtains just across the bottom of the window, as meepmeow suggests. If the landlord insists on having both halves open while you shower this might be an easy way to satisfy him.

Or if you can get an opaque exhaust fan that fits into the bottom opening you can have the best of both worlds!
posted by hattifattener at 9:21 PM on July 23, 2012

Bleach will kill mold (it will kill just about everything), but you have to dilute it. I use a 10% solution. The cdc recommends 1 cup bleach/gallon of water. I suppose that's roughly equivalent to 10%?

I say as long as you are keeping your windows open and there's not mold actively growing, your landlord should shut up. He probably would have cause to complain if you weren't venting the bathroom at all, but not venting it in the exact way he wants? Psht.
posted by Lt. Bunny Wigglesworth at 12:24 AM on July 24, 2012

I will echo those who say that it does work better that way from personal experience. I think it would be fine to open just the top, then open it all the way once you're dressed. Also, curtains will likely impede the air flow, again from experience.

Is this mold all superficial and growing on top of the paint? If not, if it is coming through from beneath, your landlord may have a much bigger problem on hand.

If the mold is just on top of the paint, one strategy to consider trying is adding another coat of pain that has mildewcide in it. They sell packets something like this at big hardware stores, I believe in the paint section. Some other paints come with it already mixed in. I haven't tried this, but I've had it recommended to me by people who have used it.
posted by slidell at 6:06 PM on July 25, 2012