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Venting two baths with one vent hood/…

| Posted in Energy, Heating & Insulation on February 28, 2002 08:47am

*
In our home we have two full bathrooms which I will be remodeling in sequence. Neither bathroom has a ceiling fan and we’ll
need to install one in each. The second floor bath is directly above the first and is located in a nearly flat roofed dormer (1 1/2 story cape.)

Can two fans share a common exhaust vent or can two fans share a portion of ductwork (assuming in-line dampers in each of the two ‘lines?’)
If so, any recommendations on the specific vent type itself or the duct (we’re in New England, so I’m assuming duct insulation is a must.)
Ideally I’d like to go through the side wall with the vent rather than violating the roll roofing with the vent and invite leaks.

Thanks in advance for any insight you may offer.
Chad

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Replies

  1. Tim_Rice | Jan 10, 2002 04:48pm | #1

    *
    Two fans can share common exhaust duct and a roof or wall cap. Most, if not all ceiling exhaust fans come with a backdraft damper on the outlet. Make sure the ones you install have these. Just have to make sure the ducts are big enough. 2-4"ducts into a 6" for 50 cfm fans, 2-6" into an 8" for 100 cfm fans. On the other hand, think about using a single fan made to ventilate 2 bathrooms. These are also readily available and usually better than the ceiling mounted variety,quieter and probably about the same cost as two "fart fans".

    1. Jeff_Maras | Jan 11, 2002 02:38am | #2

      *We have a single remotely mounted Fantech fan that is rated at about 300 cu ft per min and 90 Watts. It vents two bathrooms very quickly and quietly. Put the fan on a timer otherwise guests won't know it's on.The fan is rather pricey though. I tried using a $25 6" duct booster fan from Home Depot in another building and it didn't even open the flapper on the exterior vent hood.I would recommend a separate spring operated backdraft damper (Grainger carries them) rather than just a flapper.The Wood Doctor

      1. Alan_Kim | Jan 12, 2002 04:34am | #3

        *I am not clear on one detail with these "Fantech" setups.How do you prevent the damper from opening and exhausing the other bathroom that does not need to be exhausted when one bathroom activates the fan ?Thanks for your help,Alan

        1. Tim_Kline | Jan 12, 2002 10:18am | #4

          *Alan, Each bathroom has its own fan ducted to a Y fitting which runs a single duct to the outlet. Each duct from each bath has its own butterfly type backdraft damper which only allows airflow in one direction which obviously is out. This damper is placed in each duct before the Y fitting to prevent reverse airflow from not only the other fan, but also outside air.http://www.fantech-us.com/accessories3.htm (Backdraft dampers)http://www.fantech-us.com/index.htm (Home Page)

          1. Alan_Kim | Jan 12, 2002 05:01pm | #5

            *Thanks, Tim -I paid attention only to the small ads I've seen in FH and it looked like there's only one large fan. I guess the main idea is one exhaust out the house with the addition of remote fan/motors for each exhaust location.I will go to the site and get more detail.Thanks for your reply.Alan

          2. Alan_Kim | Jan 13, 2002 12:40am | #6

            *Tim -Went to the FanTech site and they do mention a scenario that I was asking about.For a single fan installation for two bathrooms both end up exhausting when only one bathroom needs to be vented.If two fans have to be used it would increase the cost and these fans don't look cheap.The small ad pictures I've seen seem to be a single fan installation for two areas such as a shower and a toilet stall, so activating the fan from one or the other would exhaust both areas.This solution may not necessarily be the most ideal but for more money each are could have its own remote fan motor and damper.Alan

          3. Andy_Engel_ | Jan 14, 2002 10:33pm | #7

            *Alan, these fans start at around $120 or so.Andy

          4. Alan_Kim | Jan 14, 2002 11:03pm | #8

            *Thanks, Andy -I believe there may be some misconceptions because of the way the fantech ads dipict their remote fan/motor setup.At first glance one thinks "what a great idea !".Less noise, one point of exit from the house, and a single fan/motor for all exhaust needs. (well, maybe not the kitchen exhaust).But for multiple bathrooms and stalls, dedicated fan/motor units for each area or some sort of damper system that controls the flow of air from each area is probably the more typical setup.$120 for each fan unit sounds reasonable, though.Alan

          5. Tim_Kline | Jan 15, 2002 03:07am | #9

            *Alan, We have done what you describe, run one fan for several baths, but, it complicates the wiring. Not a big deal, but something to consider. Also, it can be a little disconcerting to be in one bath when someone in another bath turns on the fan. The sound of the air moving is quite noticeable. We generally like to put these things on separate timer switches.

          6. Alan_Kim | Jan 15, 2002 05:03am | #10

            *Thanks, Tim, for confirming my concerns, which probably shouldn't be a big deal overall.But it's good to be aware of the need to have separathe the single fan arrangement.(Or have some sort of damper setup to control the flow of air.)Take care,Alan

          7. Andre_J._Ciais | Feb 28, 2002 08:47pm | #11

            *I have a problem on a two story apt. in the northwest. We are getting cups of water down thru the range hood's. The hood's are plumbed (stacked) together. The duct work is 4"x10" and transitions to 8" thru the roof. I suspect condensation, even though it seems like a lot of water. Should I wrap the 8" pipe in the attic with insulation? or install a damper to close off cold air? Thank You, Andre' J. Ciais, Republic, Washington

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