Bath fan exhaust venting

Discussion in 'Shower & bathtub Forum & Blog' started by monkeyboy, Nov 16, 2004.

  1. monkeyboy

    monkeyboy New Member

    Messages:
    4
    I would like verification that the following can be done -
    I have a master bathroom with separate toilet / shower / open areas. The toilet area has a bath fan that vents to the side of my house (stucco). The run is @15'-20'. The tiled shower area only has a light - no exhaust venting, therefore we get frequent mildew buildup in the shower. (we do have a ceiling fan in the master bath, but that does not help much).

    I'd like to install a bath light/fan kit in the shower, replacing the light - but I'd prefer not to cut another vent into my siding. I was hoping that I could use some kind of 'T' into the existing toilet fan ducting that is currently vented to the side of my house. This way, each could operate independently and I would not have to cut an additional vent into my siding.

    Can this be done with no concerns? Do I need to be concerned about duct sizes (the shower fan would likely need to be sized much bigger than the toilet fan). What about backdrafting? Any special parts I may need?

    thanks
  2. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    Use a wye instead of a tee to reduce backdraft. Also, most fans have an integral backdraft damper. If you have a 4" duct on the toilet fan, that is adquate for even a very large CFM bath fan.

    Fans and lights directly over a tub or shower are required to be UL listed for that specific application. This may limit your choices.

    In any event, such a fan must be connected to a GFCI protected circuit.
    Last edited: Nov 16, 2004
  3. LonnythePlumber

    LonnythePlumber Plumber, Contractor, Attorney

    Messages:
    319
    Location:
    Wichita, Kansas
    Larger exhaust fan

    If you have mildew then it sounds like you need a larger fan to move more CFM or let it run longer. I have not seen a ceiling fan in a bathroom. You must have a very large room.
  4. monkeyboy

    monkeyboy New Member

    Messages:
    4
    possible problem...3" and 4" ducting

    It is a large master bathroom, the only venting to outside is in the 'enclosed' toilet area (bath fan and window). This is the reason I need to vent the shower area.

    I just found that the existing ducting (from the toilet room to outside) is 3". The intended bath fan I'd like to install in the shower requires 4" ducting. Does this mean that I am out of luck in trying to tie the 2 bath fans into the same outside vent? I assume the 4" ducting above the shower would lose efficiency if I tap into the existing 3" ducting.
    If so, my choices appear to be:
    1) Run a separate 4" duct for the shower and cut a new vent in my siding for it
    2) Upgrade my toilet fan to a 4" duct, enlarge the existing vent, and tie the 2 together.
    3) Let the 4" duct share the 3" duct/vent and hope efficiency is OK

    correct?
  5. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,804
    Location:
    New England
    I'd consider a remote fan that connects ducts to both places. That way it is quiet, and efficient. You can probably replace the existing 3" vent cap with a 4" or larger without messing up the siding, but I've not done it (I'm not a pro).

    Does this have an attic above, or does it have living space above? I put in a Solatube ceiling fan/light/circular skylight in my bathroom. Very quiet, and free light. Check out their website as an option. My guess is that you could use this in the shower as well, and when the sun is up, you wouldn't need the light.
  6. monkeyboy

    monkeyboy New Member

    Messages:
    4
    There is an attic above the master bath.

    Thanks for the suggestion, but I'm looking for a quick and easy fix rather than the Solatube solution.
  7. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    I suspect you could up the ductwork to 4" and possibly keep the same outlet fitting at the exterior wall.
  8. monkeyboy

    monkeyboy New Member

    Messages:
    4
    Thanks

    Thanks to all for your responses.
  9. PEW

    PEW DIY Senior Member

    Messages:
    487
    I have coupled two together with no problem and I have coupled two together with a problem.

    Same fan and duct size with minimal duct runs and it seems to work fine.

    Different fan size and longer / different ducts you will have a problem. When both are in use at the same time, the stronger fan can reduce the output of the weaker fan to almost no discharge.

    Try and keep it as balanced as you can.
  10. stephnej

    stephnej New Member

    Messages:
    11
    Location:
    Florida
    since we are on this subject of bathroom fans, i am replacing an exhust fan and not sure how to take out the old? it's in a finished ceiling, so i don't know if it is nailed in or what. i took out all visible screws and something is holding it in. any tips?
  11. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,804
    Location:
    New England
    Some of them use hangers - sliding bars that go between the studs. Depending on how concentious the installer was, it could be a pain getting it out. Most of the time, they are just tacked in. If it is up against a joist, look for a nail or a screw through the side into the joist. WIthout access, how do you plan to get the new one in and stable? There often isn't enough play in the exhaust vent to do the wiring and make an airtight connection, then put it in place.
  12. stephnej

    stephnej New Member

    Messages:
    11
    Location:
    Florida
    Not sure what you mean. so, if it is on a hanger then what is the best way to get it out? can i just pull it down by force? also, i can see the wires and it appears that i can get my hands it there and wire it together. is a possible change?
  13. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,252
    Location:
    Cave Creek, Arizona
    fan

    IF you pull it by force you will pull down a portion of the ceiling also. Most fans are larger than the opening in the ceiling so you will probably have to cut a section out to remove the old and install the new one.
  14. Hube

    Hube New Member

    Messages:
    156
    Location:
    Ontario
    As that piece of foolhardy advice suggests, yup, your a plumber
  15. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,804
    Location:
    New England
    You indicated in an earlier post that there was an attic above. Time to crawl up there. Once there, it should be obvious how it is attached. You will be able to then make a much better connection to the vent pipe and do the electical connections as well. Probably need to be up there to get it attached properly, too. You don't want your connections on the vent pipe to be leaking. You're exhausting moist air - it will condense and potentially make a mess up there. Depending on the length of the run, it will probably get some condensation. It is much better to use the metal ductwork for this rather than the corregated stuff, unless run vertically through the roof. That way, you can pitch the run to the outside so any condensation will run outside rather than drip back into the room. Seal the joints, too. Some of the cheaper fans do not have a damper in them to block cold air from coming back into the room. This may be a useful thing to add, if necessary. Much easier in a solid vent. Most vent caps have one, but not all (they don't seal that well usually, and I personally like to have one closer to the unit. If it gets really cold there, insulate the pipe, too. Helps keep the moisture as a gas rather than condensing.
  16. RCraig

    RCraig New Member

    Messages:
    126
    Location:
    New Hampshire
    no exhaust fan in New England small bathroom

    While we are on the subject, might I also ask a bathroom fan/exhaust question. I don't have a fan in the bathroom of my small old (70s) nothing fancy home. The problem is mildew or mold, whatever that black stuff is the grows on the ceiling. A couple of years ago, a very kind painter painted with KILZ underneath, which stopped it for quite a while.
    As other people above, my fear about putting in a fan is that, although this is just a very inexpensive house (basically a tract home), it is very very tight against the very very cold NH winters. And I don't want to interfere with that. I guess a fan could be put in to exhaust either directly out (through the wall), or up into the unfinished attic, or maybe even down into the basement/garage. Any advice or thoughts would be very useful in terms of not having this turn into a fiasco. Thanks! R
  17. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,804
    Location:
    New England
    It's not recommended to vent into the attic, although it is done alot. You are exhausting moist air - anytime except the summer, it will condense in the attic, wet the insulation, and just move the problem.

    There is usually enough leakage in a house so you won't run into a problem running an exhaust fan. IF the house is truely very tight, it could be a problem (but I doubt it). If you wanted to do it high-tech, you'd put in a heat recovery system - this would extract heat from the outgoing air, and use it to warm the incoming air. Neat, but not usually necessary unless you have people showering all day.

    At least one company makes a fan control with a humidistat. It runs the fan only until the humidity drops to the specified level - this way it doesn't run forever and waste your heat and/or a/c. BTW, the heat recovery system also moderates the incoming air in the summer - it cools it as the exhaust goes out.
  18. RCraig

    RCraig New Member

    Messages:
    126
    Location:
    New Hampshire
    exhaust fan

    Ok, thanks so much for this information. I don't like high tech stuff, just more things to give problems later. Is it necessary to put in an exhaust fan? If so, if I understand correctly I might be able to run it out the wall of the house? What about the idea of exhausting it to the basement below, as this wouldn't require that I have a hole cut in my tight NE house. Also, if you have any recommendations of equipment that will not give problems for ages, perhaps you could let me know. Thanks again< R
  19. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,804
    Location:
    New England
    This is an opinion, not through experience in the trade. It just doesn't make sense to me to exhaust it in a different part of the house. Now, in the winter, it may not be a horrible thing, but there is more than water there - the perfumes from shampoo, shaving cream, soaps, etc. now are wafting around more of the house than before. Dumping it into the basement thatmay not be as warm as the rest of the house could cause the moisture to condense on the cold walls of a typical basement. YOurs may be finished and heated, so thatmay not happen. Many times, the vent is passed out through the nearest wall, so that is usually not a problem. I needed to vent a 2nd story bathroom - couldn't go out the sidewall, as it is a Mansard, and didn't want it on that part of the roof, so went up to the upper roof. I used the Solatube 10" circular skylight with light kit and fan kit. The motor is at the roof, so it is very quiet. Provides light even at night if the moon is up.

    [​IMG]
    Last edited by a moderator: Nov 26, 2008
  20. RCraig

    RCraig New Member

    Messages:
    126
    Location:
    New Hampshire
    bathroom exhaust

    Ok, appreciate your opinion and ideas. I guess my 2 best choices would be either to go out the side wall, or to go up through the attic out the roof. Either way I have to put a hole in my house, but it seems that out the side wall might be the simplest. Thanks again, R
Similar Threads: Bath exhaust
Forum Title Date
Shower & bathtub Forum & Blog Safer: Electric Space Heater Or Bathroom Heater/Exhaust Vent Feb 15, 2011
Shower & bathtub Forum & Blog Bathroom Exhaust Fan Feb 26, 2010
Shower & bathtub Forum & Blog Bathroom Exhaust Fans - keeping things out Sep 25, 2009
Shower & bathtub Forum & Blog Improve bathroom exhaust Apr 30, 2009
Shower & bathtub Forum & Blog Bathroom Exhaust Fan in Angled Ceiling? Aug 22, 2008

Share This Page