Question about Fantech Fans Exhaust Fan In-Line

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Moisture on bathroom exhause vent

I replaced an existing bathroom exhaust fan with a higher powered model. After showering in the bathroom, the exhaust vent is quite wet and actually drips water. I am using 3 feet of flexible tubing from the fan that attaches to non-flex sheet metal duct pipe, exiting straight up to the roof (about 12 feet). How do I reduce/stop the moisture in and around the vent? The temperature outdoors and in the attic is currently about 20 degrees.
........Help! Thanks.

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  • davem88 Jan 08, 2008

    Thanks but....This fan is rated for this size bathroom - it is not considered 'high' powered by any means....I'm thinking that when the warm moist steam from the shower, enters the cold exhaust pipe in the attack, it turns to water/condensation, which results in the dripping....? maybe insulating the exhaust pipe in the attack, will keep the temperture a bit warmer and reduce the creation of 'water' in the pipe....??

  • signedbybd Nov 23, 2008

    My bath fan drips water from the outside of the metal light housing. It only does this when it is cold outside. I have insulated ductwork, and insulated around the box. Help please, the water is damaging the ceiling. I have a fan tech unit.

  • Anonymous Jan 14, 2009

    Hi, we live in Alberta Canada. As you can imagine,BIG temperature changes. We noticed water dripping from our main bathroom exhaust vent. Roof mounted. Went into the attic and saw the 4" insulated flexible ducting left the exhaust port, travelled about a foot horizontally then vertically for 3ft. The cover of the insulated ducting was stapled to a vertical piece of roof truss. The duct then swung down a few inches and then headed vertical to a roof vent w/ flapper. Condensation was developing and pooling in this 'sway'. Eventually, it started to trickle down the ducting, through the exhaust port, and onto the cover plate. After reviewing some sites about this topic, I am going to purchase and install a 'backdraft flap' directly off of the exhaust port in the attic. This has got to work. If I cant buy a 4" spool piece with a flapper, I will buy a new fan equipped with one.

    Crazy thing is, we NEVER operate this fan because we don't use the tub or shower in this bathroom. Haven't for five years! Warm air being lost through the fan is causing the grief.

    Any comments?



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Another solution would be to have the exhsut fan discharge firts into a metal duct tilted at an angle so that the condensation runs away to the end of such duct.This tilted duct has a spigot on top from where the insulated flexible duct transports the air to the vertical metal exhaust duct.
The condensate water collected at the end of the duct will evaporate eventually.

Posted on Sep 26, 2008


I work for Fantech and your problem is you must keep the fan running after you shower to exhaust the humidity...I would recommend at lease 20 minutes.

Posted on Aug 31, 2008


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The fan is pulling too many cfm (cubic feet per minute).you can replace the switch of the fan with a potentiometer type switch (this works like a light dimmer)you can reduce the speed of the fan,or you can use a couple of synthetic fiber filters to trap the condensation.good luck

Posted on Jan 05, 2008

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