Bathroom fan

The house I recently bought did not originally have a bathroom fan, however one of the previous owners added one. They did a half-assed job like every other project they did to the house. The house is a standard ranch from the late 70's with a very low slope roof.
First, the fan box is not attached to the ceiling joists. It simply sits on top of the drywall. However, one edge of the ceiling hole is right up against a ceiling joist. That's good. Second, it's obvious the fan is not pulling air like it should. There is a hose attached to the box, but I'm not sure where it goes. When the fan is run, it makes a vibrating noise and there is no pull whatsoever on the bathroom door or any other sign it's actually sucking air. If I take the fan out and plug it into an outlet, it runs smoothly. I would like to install a roof vent, and attach the box like it should be.
There is little over 1 foot of space between the ceiling drywall and the roof, as seen through the ceiling hole. In addition, there is lots of blown fiberglass insulation in the attic. Needless to say, I hate thinking about going into this attic. I could easily install the vent by not going into the attic, but attaching the box is another story.
My question is: is there a fan box available that can be mounted from inside the bathroom? I'm thinking of something like the "old work" electrical boxes. I have thought about simply running screws through the box into to joist. If I must go into the attic, I can probably do that provided I wear a respirator and some sort of disposable coveralls because of the fiberglass.
Thanks for any ideas/insight.
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I'm pretty sure some, or all of the Panasonic fans will go in from beneath, just be sure the opening isn't to close to any roof rafters, as I believe these fans are around 10 inches in depth

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Go into the attic. Inspect the attic in general, and inspect the fan installation. You might find that the fan is OK, but the vent hose is blocked or collapsed, and simply needs to be re-routed or maybe just moved.
As for vibration, it's possible it just needs to have the enclosure firmly attached to the ceiling joist. It probably doesn't take much to make it vibrate if it's just sitting there bouncing around. That may or may not be easy, depending on the design of the enclosure. You might be able to drill a hole in it and run a screw through it to the joist.
It's also quite possible that the fan is an inexpensive high speed squirrel cage fan, which are quite common. Poor quality, mass produced, favored by contractors that buy in bulk and want to save every penny they can. A little bit of dust or lint in the blades puts off balance, and it vibrates. I personally remove them and throw them in the trash everytime I find one, and put a better quality unit in it's place.

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When you do go into the attic, you may find that end of the vent hose goes nowhere. Releasing moist air into a cold attic can cause condensation, mold and (in the worst case) rot. It would be worth inspecting the rafters if no one has done it in a while.
Mark
Zootal wrote:

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alt.home.repair:
<snipped>

You'll have to go into the attic to cut the hole in the roof for the other end of the exhaust pipe. Or, you could run the pipe over to the nearest soffet and use an appropriate cover.
You don't want the moist air blowing into the attic because it will cause the insulation to get wet and compact. All that moist air leads to condensation which results in mold and mildew in the attic.
The disposable coveralls are a good idea. I just take a shower afterwards to get rid of the itch. For some reason, I never have the bunny suit with me when the client needs attic work, because they always forget to mention that part of the job. Client: "I just need you to cover up the stain on my ceiling." Me: "Is there a leak?" Client: "Yes, but it's fixed." When I arrive, I find the leak isn't fixed, it just hasn't rained for three months.
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wrote on 12 Jan 2008 in group

Never tried this myself but I've heard from some old pros that if you get fiberglass insulation on you, it's best to take a shower in cold water first to close your pores. Then use hot water to wash off the fiberglass.
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I'm aware that I don't want air blowing directly into the attic; this is why I am planning on putting a vent on the roof. Now if I can just avoid going into the attic, things will be much easier. The roof of the attic is easy to touch from the fan box hole, so I can drill a pilot hole in the roof, etc.
RBM says that Panasonic fans can be installed completely from the bathroom without going into the attic. The wiring is already there, and the roof vent is a minimal problem. I've looked at the Panasonic installation instructions, and it appears that you attach a plate to the joist. This plate contains the air outlet and the wiring. Then the rest of the box is slid onto it. Can anyone verify this?
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alt.home.repair:

I can't see your instructions from here, so you're in a better position to judge that particular unit. The last time I installed a bathroom ceiling fan I drove screws through holes in the side of the box directly into a joist. If I remember correctly, the unit had some type of arms on top that could be extended to adjacent joists in case you wanted it centered.
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Here are the instructions I was looking at. The FV-08VQL4 model looks like it would work for me.
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Once you cut the opening for the fan, pull the electric cable down, drill a pilot hole through the roof, and leave something sticking out so you can find it. From on the roof, cut your 4 inch hole for the roof cap and install it. Attach a short length of 4 inch flex to the roof cap through the bathroom opening, then attach the flex and cable to the fan and install the fan from below. There should be no need to crawl into the attic
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The opening is already there for the fan, the electrical work is done, and I have a handle on the roof vent. RBM, do you have experience with the Panasonic fans? From looking at the installation instructions, it looks like I can install it completely through the ceiling hole. It appears that a plate is attached to the ceiling joist (which has the exhaust and electrical connections), then the fan box is slid onto it and attached. Is my assumption correct?
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I've only installed a couple of them, but what you describe is exactly how they installed. I found them a little more complicated than the typical Broan or Nutone fans, but that's because they're designed to be installed from beneath the ceiling
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Thanks for the quick reply. I think I'll order a couple of these and roof vents too.
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