If the bathroom is fairly small, it can go anywhere, but in the shower is best as long as it's not a steam shower. The primary goal for the fan is moisture removal. For typical "5' by x'" showers with a shower/tub on the 5' wall, I always put the fan in the tub/shower.

If the shower has a transom over the entry, the fan will do best in the shower.

If you place it outside the shower, then just outside the shower is often best.

If you have a large bathroom with a shower and a separate tub, then consider having two fans, or a single remote fan with two ventilation grills. One in the shower, one elsewhere in the bath but nearer to the tub. Especially if the tub has any bubble action, air or jetted.

The fan should vent to the outside, not into the attic, nor should it terminate in the attic with the duct end pointing at an attic vent (ridge or gable vent).

In all three of our bathrooms, the toilet is next to the tub or shower. The fan is mounted in the ceiling in all three, just in front or slightly over the toilet, in front of the shower or tub.

Here's a pic showing the fan's location in our guest bathroom:

Jenskitchen -
good question. Placement probably does not make a lot of difference if the bathroom is small. In our small bathrooms, the toilet is next to the tub or shower, so we put the fan over the toilet.

I actually put two fans in two of our bathrooms. The master bathroom has a separate room for just the toilet, so we put a small fan in there, then a large one in front of the shower in the main part of the bath. I did the same thing for my son's bathrom - it's kind of an odd shape and the toilet is partitioned away from the shower, so there is one over the toilet and one in front of the shower. In addition, I am going to put the shower fan on a timer so it runs for 20 minutes after he takes a shower. An 11-year-old boy will never remember to turn it off!

I know you did not ask about this, but here is a little unsolicited advice - look into upgrading the bath fan. For instance, Panasonic has very quiet and energy-star-certified fans for about $80 from amazon or home perfect, places like that. But my builder was going to put in the cheapy broan/nutone ones that sound like jet engines taking off! The cheap ones are $20. We ended up buying our own fans over the internet and installing them because we hate the cheap ones enough. And make sure they are big enough - the recommendation is that the air be turned over 8 times in an hour, so the entry-level ones that do 50 cfm are only big enough for a bathroom about 8 by 10. We ended up using a 400-cfm fan in our master to get enough air movement to be useful (but it is a HUGE master bath - 200 sq ft and high ceilings).

Good luck!

Thanks all. We already ordered the Panasonic based on the advice of these boards and my builder keeps telling me it is a waste but I know it was the smarter decision.

Just a shout out for the Panasonic fans, they are fabulous! My teenager takes a lengthy extra hot shower and when he gets out the mirror isn't even fogged up!

plan an air flow.

Fans work well when the air you want extracted gets replaced by other air and the flow is routed in a way you thought it would flow so there are no surprises.

You can't go wrong unless you were the guy who built our house and thought you could put one cheap Broan in the toilet closet of a 11' tall, 200 sq ft bathroom with a two person shower....I guess he thought we'd open the windows in the bathroom to defog it.

Get the biggest, quietest one you can afford and put it the closest to the source of moisture...oh and be sure it doesn't vent into the attic but outside.

Can you actually put the fan "in" the shower? I have a very large bathroom and want to put the ventilation fan in the shower on a timer to dry out the shower after use, then a separate fan for the "throne room."

"Can you actually put the fan "in" the shower? "

Yes. Unless to you, "in the shower" means in the stream of water. In that case it's "no".

Dryly, Mongo

mongo! lol!

I used an online calculator to figure the size of fan for my bathrooms. I came up with 50 cfm for the small one - (5' x 8') and 70 or 80 cfm for the larger bath (7' x 12-13').
does that sound right to those of you in the know?

what's in them now seems to be the same in both. I know the mstr bath fan doesn't work - don't know about the smaller one tho (electricity not working in there yet). but I figure if one doesn't work, the other doesn't either (or won't for long) and I might as well change them both while the electrician is out here.