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I’m finishing up an addition to my home and the question of where to vent the bathroom fan has come up. I can either go through the roof, (which I’d like to avoid as its another potential leakpath), or I can vent through the soffit, but my concern is that if the warm moist air escapes out the soffit, it’ll just find its way through the soffit vents back into the attic.
I’m thinking I should eliminate the soffit vents for 3 feet on either side of the fan vent hole to allow the exhaust air to mix with the outside air so that it wouldn’t have any chance of getting back into the attic, but before I go any further, I’d like some expertise on the best way to vent trhough the soffit (or not!)
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The first thing to do would be to cover yer butt and talk to the local building inspector. I don't have the experience to give you a definitive answer, but I would tend to think that for the small amount of time the fan would be on, it wouldn't really be an issue of the air getting back into the attic in enough quantity to cause any harm. Closin the vents on either side couldn't hurt.
Just my opinion. Hope I helped.
*Closing the vents on each side might hurt if it prevents those bays of the roof from being ventilated. If those bays don't need to be vented, why do any bays need to be vented? To maintain a cold roof over all of my own house, I connected bays that end in valleys to each other and then to vented bays. So that there was "chimney-effect" ventilation under the entire roof. Perhaps a similar approach would work for you. Skip the one or two bays closest to the vent. But put larger than normal ventilation area 3 bays away. Then drill through the rafters on the low end to vent all bays. (Obviously, the rafters have to be a bit oversized to allow for the holes).But I don't see it being a big problem in the first place. The bathroom fan runs for very few hours each day and if there is any wind, it will get pretty well dispersed.Can you take it out a gable end? -David
*art... roof jacks for 4" vent pipe are pretty foolproof... and a lot easier to install than soffit vents or thru-wall..you might want to rethink your aversion to roof-vent
*I have same problem-contempory house with knee wall shed roofs on the front on forst floor and I do not want to put the roof vents on the front - looks bad, rear of roof is inaccessible.is there a web site that shows soffit vent connections/outlets for bath fans?they are only on a short time, so draw back is no big deal to me
*Use a remote mounted fan and run 4" PVC down a wall and out the floor.-Rob
*I am rethinking it. I forgot about the venting detail as I was racing to close up the building before it got too coldthanks for the suggestion
*FWIW, In my area (NW Ohio) it is common to nail off the end of plastic fan vent just below a through-roof vent. I've only seen one (out of thousands) where there was any sign of excess moisture there.You milage may vary.
*Good points David. I figured with the peak vent in the bays in question still open, and the bottom edges of the rafters between them still open, there would be enough air movement. But then, I was just thinking of the bare rafters with sheathing on top. With insulation, sheetrock, etc., there would be no air transfer.Mike
*Art. You'll have trouble whether you vent through an unventd soffit or a vented soffit, or through the wall just below a soffit. Venting through an unvented soffit will result in mildew and staining of both the soffit and the wall. You've already noted the negative of venting through a vented soffit.If you must have a ceiling mounted exhaust fan, then feed the discharge duct through a gable end. Or try Rob Susz's suggestion.GeneL.
*thanks everyone for the adviceafter a lot of thought, I'm going through the roof. It may not look as clean, but it will definitely ensure I don't run into the problems you've alerted me toArt
*I like the idea of running it up short of an existing roof vent. I would think that you may want some sort of condensate drain in the pipe though. That moist air has got to cool down fast and condense on the inside of the pipe.
*Art. David gives some good advice. Ceiling mounted bathroom exhaust fans can result in stained ceilings, rusting of the metal parts, condensation dripping on the bathroom floor. I'd think twice about going through the roof. GeneL.
*I was wondering.....does this bathroom have an outside window ?Dispite all the talk about lost heat, etc, nothing can beat a bathroom with a window. (Especially a half bath, if you know what I mean. :-)In the winter damp air from the shower is a welcome source of humidity when the level drops down to around 30 - 40 %.All of this probably depends on what type of heat you have in the house. We have hotwater baseboard heat, which may be less affected by opening and closing windows.During the summer, depending on the conditions, we either open the window or let the central A/C handle the dampness created by the shower.
*gene...usually your advice is right on... but i've never had a problem with roof jacks for 4" discharge.. and gable ends are more prominent than roof jacks.. so they are usually uglier...b but hey, whadda i no ?
*yup, this bathroom has two large southern facing double hungs. My wife, however, doesn't want to open them in the dead of a Connecticut winter. We're still going through the roof.....
*Alan, moisture moves from warm to cold and from wet to dry. So the moisture drive in a winter-bathroom is right into any exterior wall or ceiling. Is the framing and drywall in the bathroom airtight? Andy
*Andy - if you were addressing me instead of Art, our bathrooms are fairly tight and the indoor temp is kept in the low 60's.When we want to vent the bathrooms after a shower (we don't take hour long steam showers as some folks do), dissipating the moist air either out the window or into the living area is never a problem.Yes, the aluminum window will get condensation but not enough to start dripping down onto the wooden stool and cause damage. It usually clears fairly quickly.Also, having hotwater convector loops running under most of the windows seems to do an excellent job of preventing condensation on the windows dispite them being old aluminum frame with steel storms outside.Our walls are well maintained plaster on rock lath with latex enamel in the bath walls.
*Alan, I just took your post as an opportunity to talk building physics. FWIW, my baths are vented with an inline fan that vents through the roof. Works great, except that when the temp gets way down, some condensation can drain back. Try as we may, there hasn't been a perfect house built yet.Andy
*re - "Try as we may, there hasn't been a perfect house built yet."---------Yes, and it is so easy to get caught up in the daydreaming of "Fine Homebuilding" with some examples I considered perfect in my eyes.
*My house is perfect, when I wake up on Christmas morning and see the delight in my boy's eyes. Andy
*Perfect, Andy.We have six young eyeballs, all belonging to boys.Getting tree sometime this week.
*quite right!My house is striving to become more perfect. The bathroom is on an exterior wall, but since the walls are SIPS (OSB/EPS sandwhich), I'm not sure how far the moisture will go into the wall.
*I have a NuTone QT-200 that I vented out the soffit for the sake of appearance. Hard-ducted (4 x 10) with damper near the discharge point, duct pitched to the grille and well-taped in the attic. No soffit vents (end louver).Absolutely no problems, no dripping, staining etc.Jeff
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I'm finishing up an addition to my home and the question of where to vent the bathroom fan has come up. I can either go through the roof, (which I'd like to avoid as its another potential leakpath), or I can vent through the soffit, but my concern is that if the warm moist air escapes out the soffit, it'll just find its way through the soffit vents back into the attic.
I'm thinking I should eliminate the soffit vents for 3 feet on either side of the fan vent hole to allow the exhaust air to mix with the outside air so that it wouldn't have any chance of getting back into the attic, but before I go any further, I'd like some expertise on the best way to vent trhough the soffit (or not!)