Bathroom Exhaust Fan

Discussion in 'HVAC Heating & Cooling' started by Jedi, Apr 22, 2007.

  1. Jedi

    Jedi New Member

    Messages:
    23
    I'm remodeling my bathroom and one of the first things I'll be replacing is the exhaust fan. My home is a 1 story home and I have a stair case up to the attic which is just insulation and about 6' tall in the middle. Today I went up there and was surprised to find that I have a double ceiling in the bathroom area. Should I pull the ceiling and add vapor barrier or should I just leave it? Secondly I was going to use a rigid line for my exhaust, should I run it straight up/over/and through or over/up/across and through or should I just buy a flex line?

    Thanks

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  2. what do people do in your area? Is it humid enough to justify vapor barriers in bathroom ceilings? I'd not put a vapor barrier in. I'd put a few dollars into a "rigid" exhaust line, one with smooth sides. Not the one shown in these 3 pictures. I'd put a lot of money into a quiet fan on a variable speed controller; that's because I need the quiet.

    David
  3. Jedi

    Jedi New Member

    Messages:
    23
    I've bought the NuTone QTRN110c which is rated at 110 cfm and 1.5 sones and will be putting it on a timer. Compared to the the one I have now it's much more powerful and it doesn't sound like a jet engine which will be a nice improvement. I did buy some 4" rigid but I'll have to buy some more and some 45 degree elbows.

    Thanks,
    From the Great White North
  4. leejosepho

    leejosepho DIY scratch-pad engineer

    In my own opinion, no. The flex has more friction and restricts flow, and moisture can accumulate in the corrugation.
  5. if you are that far north then you need more insulation. I saw your photos and I read that you have a 1-storey.

    A radiant barrier insulation, like a foil faced foam panel, will be a vapor barrier and more. It'll seal the envelope between conditioned space and unconditioned space. It'll reflect a portion of heat energy that conductive insulation never catches (known as radiant or radiative, it is the heat energy you feel coming through space when you stand next to a fire.) It'll also be an additional layer of conductive insulation.

    david
  6. Jedi

    Jedi New Member

    Messages:
    23
    Is this foil faced foam panel material available at Home Depot? I assume this should be used in the space between the two ceilings.
  7. i've seen it at Reno Depot stores in the aisle at the far end where they also have foil faced bubble wrap insulation.

    Both HD and RD stores are run by individual decision makers who may or may not stock whatever they wish, within certain limits, so you'll never know unless you phone the store first. They'll always tell you what they have, but not the price. The product is not a "standard" in every store.

    Unfortunately this may sound like a wild goose chase. I'd check the 411 web site and call each store in a row, and ask for whoever handles the department that insulation materials are in. Ask if anything is foil faced.

    david

    edit: i just remembered, that I actually bought at HD a rigid 4'x8' panel of foil faced product and I still have a piece of it right in front of me. Here is what it says on it: "ENER MAX" BP "acoustical barrier" ((not a big concern if they sell it as acoustical insulation)) with "supported vapor barrier" : 0 Perm (whatever that is); "supported air barrier": 0 L/(s mm) at 75 kpa(whatever that means); structural insulation: R4.7, with an asterisk describing more... So the good news is that you can get something foil faced at HD. It is wood fiber semifluff that you can slice with a bread knife, covered with a tin foil like membrane.

    p.s. just f.y.i. there are no R values associated with radiant heat energy transfers. No R value lab test can measure it, as the test is not designed for that purpose. I predict that our grandchhildren will look back at this period and say that we just didn't get it. If kilns can insulate thousands of degrees of radiant energy, why can't building insulation also have a layer to stop heat from radiating through space too?
    Last edited: Apr 23, 2007
  8. Jedi

    Jedi New Member

    Messages:
    23
    Are you suggesting removing the lower ceiling? That's the only way I think of getting insulation into the section between the two ceilings. It looks like to me that the upper ceiling was only cut out in a 2'x2' section directly about the fan.

    BTW - In the past the ceiling in the bathroom was always wet after taking a shower. I assumed it was a combination of long hot showers and a crappy fan. Today my wife had to go to work early and showered 30 minutes before me and after my shower the condensation that was accumulating of the ceiling was so much that it was starting to drip. I assume this has something to do with the fact that yesterday I removed a bunch of the insulation out from around the fan to look at it.
  9. it may be unimportant. If you observed and compared with winter conditions, with numerous data points, using thermometers and hygrometers, we might have a valid data set. It isn't winter now, and so anything that happened today isn't indicative of much. No matter where you are geographically, what your climate is, and what today's weather is.

    I doubt that I can add much to your thinking process. I don't know what your double ceiling is. In your pictures I believe I saw two layers of drywall. If that is what you meant, then my reaction is "it's not a concern, not a big deal". Two layers is just thicker drywall; treat it psychologically and analytically as if it were a 1" layer. However, experts may have other comments on vapor barriers and double ceilings.

    A lot depends on local building practices, what will be deemed the right way to handle humidity. Note that closed cell foam can handle the dew point freeze point better than any air permeable matter. The big goal is to avoid letting humidity buildup and freeze in your organic building parts (wood, drywall paper facing). The dewpoint at the building envelope during winter. My saying this does not mean I can advise you more. I may already have said things not quite right and may get corrected.

    What climate are you in?

    david
  10. Jedi

    Jedi New Member

    Messages:
    23
    I live in Winnipeg, Manitoba.

    I'm not sure that you understand what I mean by a double ceiling. If you look at picture fan2 you will see a 2x4 with red writing on it. That is the new ceiling (the lower ceiling). Above that there is a gap of about 6" and then a 2x8. If you look closely at the bottom of the 2x8 you'll see that a 2'x2' opening was cut into it to make room for the ceiling fan. So the order is bathroom drywall, 2x4, 6" gap, drywall, 2x8. I hope this makes more sense.
  11. leejosepho

    leejosepho DIY scratch-pad engineer

    Unless that condensation was especially concentrated around the area of the fan, I would doubt your removal of insulation from around the fan was the cause of that unusually high level of condensation. More that likely, that was simply the result of back-to-back showers and not previously noticed by yourself.

    If that was my own project, I believe I would simply install the rigid vent line and close everthing back up as it was ... and after checking to be sure the wiring to the fan is the type that can be safely buried in insulation.

    I would not install any kind of vapor barrier, and I would consider a dehumidistat (along with an over-ride and/or timer switch for removal of odors, if you like) to control the fan and humidity in that bathroom.

    Removing the lower ceiling could be a good idea if you want/need the extra ceiling height, but that present void is a dead-air space that actually adds a little to your overall insulation.
    Last edited: Apr 23, 2007
  12. OK then you may have enough insulation, if it goes back in the hole, the hole gets sealed, and then more insulation goes back on top of that, to the level of the 2x8s. A lot of air can leak out there if you don't tape it airtight. From what I have read about your standards as a homeowner renovator, I would still add a layer of foil. On top. I don't see any reason to undo anything.

    Every house in your climate will have a whole-house vapor barrier. A "Tyvek" housewrap. Winter winds (minus 25; 50mph) will suck heated house air out very fast. Some people put a damper on their exhaust fan ducts (bathroom, kitchen, dryer) so that they can prevent air from being blown outside during the worst conditions. What a paradox: at first you want ventilation, and then you don't.

    David
  13. Jedi

    Jedi New Member

    Messages:
    23
    Thanks a lot for all your help. I'll be picking up some 45 degree elbows and another piece of rigid line.
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