Condensation inside bathrrom vent fan

[Bob]

I installed a Panasonic FV11VQ3 110 CFM bathroom vent fan in a small bathroom. Works like a champ. No steam on the mirror and within minutes (with door or window open) majority of steam is cleared.

My one problem is this; I get standing water inside the fan. I wrapped the duct work and unit with insulation; still condensation turning into small pool of water. I check for leaks in the roof cap... none. I switch the duct work from the stiff flexible/expanding type to the smooth normal duct work; still get pool of water.

I researched google groups and some people recommended running the fan before starting the shower to warm it up. I don't think this is the issue because I did some "condensation" tests in the middle of the afternoon and it was not cold in the attic. I will still try this though. Also another person recommended having a door slightly open or a window. I will do this as well.

Would anyone have any other suggestions in case this does not work? One thing I will mention the instructions ask for 2-3 feet of horizontal pipe before going to the roof cap and I have 1 foot due to space issues. I mentioned this to some people with building experience and said this should not cause a problem.

Thank in advance.

[Dick Russell]

If the water collects only during/after the shower operation, so that you know that leaking from the outside is not the source of the water, then it is simply a matter of water from the shower condensing in the duct and running back to a spot where it collects. The advice to turn the fan on just before turning on the water is good. Hot water generates a lot of water vapor, which moves rapidly through the room and starts condensing on anything cooler, including and especially the duct going through the attic. Moving air through the duct from the moment the water is turned on moves much of the moisture generated straight outside and to some extent localizes the humidity to the shower stall itself. You also want to leave the fan on for several minutes after the water is turned off, to give the duct a chance to dry out. If you wait until you are done with the shower, then you're too late; water has condensed in a film on the mirrors, walls, duct, and even inside the walls if the bathroom doesn't have a really good vapor barrier installed. Trying to revaporize water condensed on the walls after the fact is harder than simply moving the vapor outside before much condensation takes place. You also need to make sure that the air is flowing, which can be done by going up on the roof while the fan is blowing. If the flapper is stuck, and little air is flowing, then the only thing drying out the room is the open door and window.

[PipeDown]

It's clear you discovered the reason for the recommendation of having a short horizontal run. The run should be close to the fan not close to the vent cap.

Just because the air in the attic in the afternoon is warm, dosen't necessarily mean the vent pipe and anything it is resting on/against is also warm. All you need is to have something below the dew point to get condensation. Since the dew point is relative to the RH, a steamy room condenses on fairly warm surfaces. At near 100% RH, water will condensce on just about anything.

Even with a 150W heat lamp in the vent (my setup) I still get condensation from overflow from my (new) steam room. I may need to move the vent pipe to mitigate also but I think it does have a horizontal section near the vent already. I need to look more closely to see how much is condenscing in the fan housing itself before the pipe.

I may try to put a dip in the vent pipe (using metal flex pipe) to see if I can make some sort of P trap and poke a hole for drainage to a pan. I don't expect more than a few ounces per day so it should evaporate without any further draining (never reaches freezing at my house in CA). Still thinking of that solution as it could make for a bacterial breeding ground if the water does not evaporate daily.

Another solution I am considering is to snake a short piece of wire in the vent to encourage the condensate to drain where I want it (not dripping from the middle of the heat lamp). I can probably collect it into a sponge which will be dried by the adjascent heat lamp. ( I will try this first as it does not require access to the attic)

[hallerb]

is the vent line and fan insulated from any cold area?

the warm moist air touches the cold fan or line and instant drip.

insulate the entire area very well

[Bob]

Thanks for the quick input. To be clear the condensation is happening inside the fan itself, the duct work is bone dry except where the "male" duct part of the fan receives the "female part" of the duct work. The water inside the fan will drip onto the duct connection, other than that dry. As far as inulation the fan unit is wrapped and the duct work as well.

Also I have not sealed the joints with water proof tape due to the constant removal and installing for troubleshooting. Can this be an issue as well?

Pipedown, if all else fails I will move the fan 1 1/2 feet to meet the specs. I'm hoping after that undertaking that the problem will no longer persist.

So it seems these are the standar remedies for condensation in the bathroom fan:

- Insulation is needed around pipes and fan

- Open a window or door slighty to allow better air flow.

- Turn fan on a few minutes before shower to warm up fan and minimize condensation inside of unit.

- Let fan run for a while after to evaporate all steam in unit and duct work.

I will try #2 and #3. If this fails I will reposition the fan to allow for a longer horizontal run as recommended by the manufacturer.

[John Grabowski]

I'm wondering if you have good air flow? Have you checked the outside vent to see if air is actually coming out when the fan is on. It is possible that the vent flap is stuck. If you are using flex duct check to make sure that it is not crushed anywhere. Are you able to see the fan blade spinning at high speed? Make sure that the damper on the fan is opening when the fan is on.

[Bob]

Well the weekend has past and here are the results of my troubleshooting. For the sake of being brief I will use bullet points:

- With the Window open for more air flow I still get condensation insided the vent fan.

- With insulation around the air duct and bathroom fan I still get condensation inside the vent fan.

- I switched to the smooth metal air duct instead of the flexible type; condensation.

- I ran the fan for 5 minutes before running the shower and for 5 minutes after and still condenstaion.

- When I turn the fan on I can hold a piece of paper by the fan and the paper will stick to the grille.

Also just to be clear the condensation will build up over 2 days to form standing water and ends up dripping out of the fan.

The vent flap on the roof vent opens when the fan turns on, the flap on the fan is opens as well. The condesation is not coming back from the vents because I have a slight angle going down, away from the fan.

A couple of other items for thought. My bathroom fan is in the attic about 3-4 feet away from a soffit vent. It's not directly by it but it's in the area. Also I am using aircondition/heater vent insulation; about 3/4" thick. Could these things be an issue?

The next thing I am going to try is remove the flap from the fan, to see if this allows faster airflow. Also someone mentioned to me that it's possible that the climate in my house and attic is just going to produce this affect of condenstaion so I might need to figure out a way to get the condensation out. Possibly there is a fan made with some sort of drip that I can attach pipe to to channel the water out; similar to how A/C. Any thoughts on this.

[PipeDown]

Insulating the fan box then preheating it before running the fan might help but if you read my earlier post, I suggest it's a lost cause since very humid air will still condensce on even warmish surfaces because the dew point is raised so high when steam is present.

I suggest instead of preventing the water, deal with it instead, give it a place to collect and drain or better yet, evaporate. A sponge or cloth inside the housing will absorb the water and with its large surface area, evaporate that water more efficiently than standing in a puddle.

Checking the Broan website they suggest the same advice you already have, namely the condensation is from cold duct work. My observation and seemingly yours is that most of the water is forming on the fan metal housing moreso than the duct. In this case insulate more directly on top of the fan and make sure the flapper is closing so cold outside air does not chill the housing more than necessary

[John Grabowski]

I don't think that I have ever heard of this problem before. A few things come to mind such as the CFM and the size of the duct. I have seen instances where a 4" fan outlet is reduced to 3" duct. I am also wondering if maybe your bathroom is too cold. Perhaps a bathroom heater might help. I am just guessing here as I thought that the insulation would have corrected the problem. This is a long shot, but are there any water pipes in the vicinity of the fan?

Before you use the shower and turn on the fan does it feel cold? Do you feel cold air coming out of it? What would happen if you used the fan without the decorative cover on? Where is the fan in relation to the shower?

[Stretch]

Bob,

I have seen this kind of problem when the fan is not sealed to the ceiling. Where the fan housing penetrates the ceiling, seal around it in the attic with expanding foam. This keeps the attic air from being drawn into the fan housing along with the room air when the fan is runnind, as the inside of the housing is under a vacuum. When the humid room air mixes with the cold attic air, it causes condensation inside the fan housing and on the surface of the fan grille. You could also use silicone. Make sure you leave the grille off while the foam or silicone is curing, other the grille will be glued to the fan housing. Note this can also happen in the summer with humid air in the attic and the room air conditioned.

Stretch