I have a bathroom fan which feels like it must move 7 CFM, if I'm lucky.  I have taken the cover off and vacuumed all the lint/crap out of it, but still no bueno.  The opening is roughly 7"x8.5" and I am having trouble finding a replacement fan that would even fit.  

Is this something that I can just cut a larger opening and put in a new fan, or is there a 7"x8.5" fan on the market that doesn't stink on ice?

You can just buy one that is bigger and cut the drywall.

1) Buy panasonic fan

Just replaced mine a few months ago and had to cut the drywall to make it fit.  That said, I didn't do a good job and ripped a little more than I should.  Some putty helped fix that, but I still have to paint it.

I had a POS fan and went to a Broan that is super quiet and moves more air too.  The hole had to be cut for the larger vent.  Well worth it though!

I just replaced one of mine with a NuTone that's pretty great.  It was a "no above access" type kit.  Had to cut a bigger hole, and I ended up pulling new hose because I didn't trust what was already there.  PITA but worth it.  The damage I was getting from humidity was really screwing with things.  I replaced another one with a Broan that I like.







 

This is the correct answer; but it is incomplete.

That Panasonic fan?  The best.  However, ones that move a good amount of air (150 CFM+) will require a 6" duct.  

It's worth the extra work to install the fan + ductwork.  I just did it on our master last weekend and will do so on our other three baths this winter.

This gives an opportunity for a good, maybe stupidly perceived, question:  When installing a bathroom fan, where do you send the air?  My house had nothing but the box and the hole for exhaust going straight into the insulation.  So I put a pvc pipe about a foot up and it just exhausts into the attic.

You don't want the humidity going into the attic.  It is supposed to vent outside.

No bueno.  Should exhaust to the outside; either through a wall or through the roof.

Ahh that sucks.  Gonna have to figure out a way to cut a hole in the roof.

Or vent out the soffet, or vent out a wall. I try to avoid more holes in the roof.

Soffet is about 10ft away, while the dryer vent hole is about 25ft.  Dryer vent is easier to get to, but farther away.  Think that will be a problem?

If you're talking about the dryer and bath fan sharing the same vent, no.  There's not enough free area in a 4" pipe for both.

Couple of things I'd recommend:
1. Replace the switch with a timer — you want to run the fan until the humidity is dissipated so that it doesn't condense in the venting. I usually run my fan for 15 min after my shower is over.
2. Insulate the duct work and make sure it doesn't slope towards the fan or run the duct vertically so it acts like a chimney.

Easy:


I would not recommend venting though the soffet.

I've been thinking about a timer/humidistat.  My parents think I'm crazy, but I replaced all the light switches in my house, a few with occupancy sensors and the porch lights on Honeywell timer switches with sunrise/sunset.

Do not share a vent line with any other exhaust.  It can be done but you cannot simply use a tee or wye fitting.  Venting out the soffit is not allowed by code in some areas.   I hate holes through the roof but they are necessary to vent properly.  I added 3 exhaust vents to my roof just a few months ago.  Old construction is old code allowed to vent into the attic.  

Braun and Nutone are the same company now so the fixture housings and motor are often the same.  The exterior light and grill may be different.

I did not use the Braun roof vent.  I found it to be too short and too close to the roof and may block air flow with snow on the roof.

I used a hole saw to cut the roof plywood a half inch bigger than the ducting I was running.

OP, no worries. I've been in your shoes before. Like others have said, just buy a bigger fan and cut the drywall. You may not even need to install new ductwork...I didn't. It's easy; if you can remove an FSP and install a lo-pro gas block, you can do this.



True, but a lot of guys have said it is copacetic. Must be an older house thing...mine was built in '71. I wouldn't get into the potential maintenance nightmare of cutting a hole in the roof if everything has been working fine.

Now that's a word I only pull out when I've been drinking for hours!  

If you have asphalt roofing, follow the video above and add a vent, just set the saw shallow so you don't cut into a rafter or truss. I have seen very few houses that had adequate venting. They are about $15 or so. Run flex hose up to the vent and attach it so the end is up inside the vent.

Meche 03 says not to tee into another exhaust, how come?  I am just about to do this.  
Our master bath has no exhaust fan.  The adjoining bath does and it's exhaust duct would be
Very convenient to tee into.

No bueno?

Without both fans running simultaneously, you'll just pump about half the humidity from one bathroom into the other.  To avoid such an effect, you'd have to install a pair of check valves.....or just vent individually to the outside.

Ok, thanks.  Time to rethink it.

OK, thanks.

The fan I just put in has a damper in the exhaust shaft.
I had my ceiling open anyway for a leak on my 2nd floor so I was able to remove and add a larger fart fan.

The damper, check valve flapper,  keeps air from being pushed back through the fan.  Typically, that is to keep wind blowing across the exterior exhaust vent from blowing outside air into the house.  With the Tee or Wye connection you are using the damper as a check valve in a way but it is creating a dead head area between the tee and the exhaust fan.  That dead head area can collect moisture.  If both fans are running at the same time the section of pipe between the Tee and exhaust will build up extra back pressure and may not allow sufficient air flow and decrease the performance of each exhaust fan.  

On the flip side, it will work.   maybe not properly or at peak performance but it will work.  If both fans have a damper, you use a wye fitting, and run the fans after a shower until the room is "dry" then you most likely wont see any negative effects.  It will be better than no fan and a fan exhausting into the attic.  

I recommend a wye fitting because it will flow better than a tee fitting.  The tee fitting really restricts air flow.
If at all possible have the two inlets sized for your exhaust fan diameter, usually 4 inch, and have the outlet of the wye 6 inches.  The increased diameter allows for both fans to run at the same time without causing a flow restriction as the 6 inch has almost twice the cross sectional area as the 4 inch.