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Placement of new bathroom exhaust fan


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Hi all! Well, I'm here naturally, with a question. Long story short - our bathroom is too humid, so I took the 15 year old fan out and put in a new one.

- old was in toilet area (you can sorta see the door into it on left side of pic of new fan. It was 50 cfm, and the vent ductwork was pointing the wrong way and so made a 180 to go out of the house (over shower), and it was confined in that room.

- So, I took that out, came outside of the room, got a 140 cfm, mounted it the correct orientation. So now it is not in the room, and probably 6ft less duct travel time with no bends.

But here is my concern, now that I have it up and the dry wall started, of course. Is it a problem that it is right above the door out of the bathroom? Will it just pull fresh air from there and blow that out and not actually vent the steam/moisture from the bathroom??

I can move it one or two joists toward the middle of the bath but .. well, frankly I'm in deeper than I want to be already LOL. (I've never done drywall). Then it would also have at least one possibly two bends in the ductwork going out and be longer again.

So. 1) above door, but out of bathroom at least, 10ft or so run to side of house, no bends, start repair.

Or, 2) lots of work to move a joist or two, add 4 or five feet of duct, 1 or two bends, lots more repair.

I do think 2 would be "better" in a perfect world, but is it fine enough as is (without the added loss of CFM due to the bends) to justify skipping all the work? Will the steam rise above the cool air of the other room anyway so, no worries?

(also note, there is a second sink to the right of the one you can see, across from the toilet room section, and the air supply register is directly below the new location for exhaust, on the floor in doorway coming in)

Help! And, thanks :)

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Most people should close the bathroom door when they shower. [:)]

So the fan will work fine when needed most. Install a digital timer switch on it, hit 20 mins and leave the door partly closed when you head out. I think it will be fine as is.

Code toadys might protest that you need a fan in the toilet enclosure as well, separate room. Moisture is not an issue in there, so that is more a lifestyles issue. If someone raises the issue of venting the crapper room, cut the door off top and bottom like a public washroom. Or take the door off.

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Moisture laden air is lighter than dry air and rises to the top of the room. Since that's where the fan is, that arrangement works pretty good.

Try to see the effect of the fan as lowering the pressure throughout the room. The incoming air will come from wherever it can. If you leave the door open then most of it will certainly come from there. If it's close, it'll come from the gaps around the door, the register, and from any cracks or openings in the room. It's got to come from somewhere or the fan won't be moving any air in the first place.

Make sense?


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Thanks for the replies guys. Yes it does make sense, I'm just hoping to not have the effect of air coming straight through the top of the door way and straight up into the fan, thus leaving all the rest of the bathroom stagnant.

I've got conflicting thoughts on open vs shutting the bathroom door. If it wants to move 140 cfm, wouldn't I chock the fan by closing the door, thus turn it into a 70 cfm, effectively?

Though, between the door cracks and the floor register I would think it would come close. Perhaps cracking the door is the best compromise.

I have to count on turbulence, and/or moisture/humidity rising above cooler air, to feel comfortable with it, I think. Warm air rises so, Yeah I think the cool from the doorway would/should just kinda go under the warm air and keep the flow working well. (Especially with the two foot of wall above the door to hold the warm air)

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I have a problem with my master bathroom fogging up badly when the spouse or I takes a shower. It's such a small room, the moisture has no place to go. It does have an exhaust fan but that doesn't work nearly as well as simply leaving the door open when we shower, so that's what I do now.

Problem is nearly solved.


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We don't get any fog but it ranges from 60-75 humidity depending on the day / hvac / etc. It'll hit 65 with no shower yet that day and just feels humid. Rest of the house is around 55.

Take a 3 min moderately hot shower and it'll get into the 70s (with the last fan).

I'm wondering if its just fairly chronic and each shower is agitating things even when fast, never completely dry. I know the floor of the shower pretty much never dries with me showering in AM and her showering at night. Even going 24 hours in between its still a little wet.

Tub dries fast though.

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You know, the supply register's ductwork is no smaller than the vents so, Between that and the near inch gap under the door, I don't think I'm too worried about having the door shut and really reducing efficiency or harming the fan.

Two showers since install, have fared real well. It really seems to move the air!

The room itself is just higher humid than the rest of the house and I don't know what much more I can do about that. I accidentally left it running 3 hours this morning, it was still mid 60s Rh. Still wet in the shower (that will be wet non stop unless I can sort out some circulation in there).

So, I think the fan itself, its placement, etc, I'm happy with. (and it's of course so much quieter!)

If I want to improve further I'll have to take other measures.

Thanks again all!

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While I do have a box fan or two, I'm not sure I want that as a permanent solution! As for humidistat.. well, as I had left it running accidentally for 3 this AM with the humidity still not going below 65.

(sometimes its in the 50s tho, just depends on the day)

I don't et the wall mount fan heater. I don't want more heat in there that's for sure!

One option I guess, an old school rotating table top fan, just put on the counter and blow air into the shower for a few minutes when done.

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What kind of instrument are you getting your readings from? I have seen the cheap hardware store hygrometers off by 10%RH or more. You need to invest in a good instrument, and/or double-check yours against others to know that you are getting accurate numbers.

After a shower, all the water on the tile surface has to evaporate, and all the moisture in towels you hang up has to do the same. Water continually evaporates off the surface in the toilet bowl. There are sources of humidity in the bathroom that really aren't anywhere else in the house, so a slightly higher number is unsurprising. In our house, the bath fan runs at least one hour after a shower, more in the wintertime when I am also using it to remove humidity from the house in general.

I just had one of these controls installed in a customer's house, because she line-dries laundry in her laundry room. Cost about $30. http://www.leviton.com/OA_HTML/ProductD ... site=10251

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