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Vent fan leakage

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  • Vent fan leakage

    Hello, I am new to this forum and this is my first post. I hope to get some advice regarding a bathroom vent fan. My house was built in 1985 and the builder had installed entry level bath exhaust fans made by Neutone. They were simply exhausted into the attic space. The attic has very good ventalation, back in the fall I reroofed the house and installed full ridge and equal sofit vents. I recently updated the fans in both baths. The main bath where the showers are taken is the problem. I replaced the original fan with a Neutone 300 cfm model which works fantastic, no problems with moisture or condensation during showers. As the builder had originally terminated the fans into the attic space I assumed it was ok, so I did the same with the replacement units. The original fans used 3" or 4" white flex tubing, with the unit I installed I used 6" ridgid Aluminum duct vent (smooth bore). This runs upward approx. 6'to 8' ft. to the ridge vent at the peak of the roof where I installed a 90 degree elbow and pointed it downward so warm moist air would no be blown directly onto the underside of the roof which is 3/4" plywood, I figured if I difused it downward it would not condisate onto the plywood and potentially cause a mold or rot problem. I don't know if this was correct thinking or not. Everything was fine untill the weather got real cold, I live in mid Michigan. When we'd use the fan during showers, water started dripping from the cieling vent cover onto the bathroom floor, not terrible but annoying, once it got real cold -10 to +20 it would actually pour in almost a steady stream and we had to use a bucket to catch it. We've since stopped using it during showers to avoid the headachce, problem is its still leaking, even 10 hrs. after the last shower, however its a slow drip every 10 seconds or so, even while off during showers it drips every 1 to 2 seconds. I'm assuming even though the fan has a internal plastic door that flips open when on, the warm air from the house is drafting up past the plastic door into the very cold pipe, condensating and then gravity kicks in and it drains right back into the house, If I insulate the pipe will this solve my problem? Or do I have to reroute the pipe and vent it out a soffit vent on a negative angle pitched down from the fan and not up towards the peak of the roof? Or do I need to do something altogether differant? I'd appreciate any advice as we've had it with buckets and towels. Thanks Frank J.

  • #2
    Venting into the attic is a bad plan, eventually you will have mold growing everywhere. The quickest fix at this point without putting a proper vent in would be to find the closest roof vent to your fan and run insulation wrapped pipe up to it and allow the moist air to blow up and out of the attic vent. The pipe should be as close to the critter screen on the vent as possable so the majority of the moisture blows out. If your only roof vent is the ridge vent I dont think it is a good plan to run the pipe that far up in the attic as you will likely have condensation forming no matter how well you insulate the pipe, the round roof vents are usually farther down the slope than the ridge vent. Another option would be to use insulated flex pipe and run it to the closest soffit or end gabel and put in a proper vent with screening to keep birds out


    • #3
      wbrooks, thanks for the heads up, I will do it the right way and reroute the pipe to the gable end and vent it out as you suggested,the entire length of pipe will be under the blown in insulation.


      • #4
        As an air conditioning mechanic working with new construction, I see this often. Here's the proper method of venting bath fans as per the international building code, flex duct can be used as long as it's metal, 3" or 4" depending on the fan and cfm output, run the flex as close to the ceiling joists as possible to the nearest soffet vent. DO NOT run the flex upwards as any moisture that builds up will drip down back into the fan causing major problems. I live in AL where moisture is a severe problem, and I've never had any call backs on this application.