It is winter again and I get a constant drip from both upstairs bathroom vents. The vents are located right over the stools. It makes for an unpleasant time, especially for the women in the house.
Here is what I think is happening. The warm moist air in the house (we run a humidifier) contacts the cold air in the attic vent. The moisture condenses and then possibly freezes. We set back the thermostat at night and when we are at work. When the temp rises in the early morning and evening, the ice melts, causing a drip.
The vents are low end models with an exhaust port on the side. The vent bends up 90 degrees and exits in the attic beneath a roof vent. There is 10″ fiberglass in the ceiling surrounding the vent. I assume the cold air sinks down the vent and chills the unit. I have no problems when the temp is above freezing or during rain storms.
Are there better models? Different models? Would I have the same problem even with a different model? Were they installed incorrectly? Any ideas on how to correct?
Thanks!
EricS
Replies
If the winter air in the house is so dry that you need to run a humidifier, you might try just not running the vent fan in the winter.
Is the entire run of the vent pipes insulated ?
If not, there's your most likely biggest problem.
And, you need to allow them to run for a while after you're done producing water vapor in the shower, etc.
It is a flex pipe and not insulated. We use one room primarily for showers and run the vent for while. It is of marginal benefit. the other room does not generate moisture from showers and still drips.
I'd try insulating those duct runs first before resorting to more drastic measures and reconfigurations. I'm not a big fan of the flex ducts for various reasons and so would recommend relacing them with rigid.
The fact that running the fan for longer periods of time doesn't alter or benefit the situation isn't hard to believe since your ducts are long and uninsulated. The longer you run the fan, the more moisture laden air you're introducing to the chilled uninsulated ducts. Consequently, more condensation could occur than if you didn't run them at all.
If the walls of your house were constructed of the same thin plastic material as those ducts are....they'd condense and sweat, too. :-)
And if those flex ducts have a low spot in them where water can collect and freeze, it will. This would not only obstruct the flow from the bathroom, but aid in producing more moisture as the warmer air melts it when you run the fan and consequently you could have more condensation.
I'd suggest trying the insulation and seeing what happens. I'd also inspect/remove the flex ducts and make sure they don't have a lump of ice in them somewhere.
Knowledge is power, but only if applied in a timely fashion.
When I put mine in I thought I would be smart and tie three together, one in the laundry room to pull out heat in summer as well as cat box odors sometinmes, one in a powder room, and one in shower/toilet area. Used flex to join to a manifold consisting of thinwall pvc with a couple of tees. I ran it up through the roof and left about a foot above the jack and installed a dryer vent.
First winter went into powder room and had good (bad) puddle on toilet and floor. Opened up and reached in to find a lot of water in the flex. Went up and wrapped all exposed with r-19. Went up on roof and reduced the stack to minimum and made sure any condensation generated in the 90 and vent would drain out rather than down pipe. I think I solved it. Never would have thought it would do this. Fortunately my flex is pretty well buried in cellulose.
Your idea of trying the simple things first makes sense. I am wondering though how to insulate a flex pipe that snakes its way to the ridge. It has to follow the pitch of the roof (12/12) so there is plenty of surface to condense and drip. Wouldn't the cold air still work its way down the pipe anyway? insulating the outside wouldn't help the far end of the pipe. I'm wondering if I just move the problem farther up the pipe.
Any additional thoughts?
Thanks, Eric - KC
As I envision your situation, I'm now going to highly recommend that you replace those flex tubes with rigid pipe. The reason for this is that if you've got the standard flex stuff, it has ribs in it comprised of wound wires to give it form. The resulting surface is not smooth and true, but uneven and therefore air moving thru this type of duct will create eddies that impede the efficient flow. The longer the tube, the greater the resistance to flow that develops. This may be one of the biggest reasons you experience little benefit from running the fan. And if your current install allows that flex duct to curve around in an up and down, side to side fashion.......like a snake........I wouldn't be surprised at all if the remaining force at the roof vent can't even open the damper. Running an efficient duct is quite different than laying out a piece of wire or an extension cord.
If you replace this flex with rigid pipe and try to use as few elbows as possible, the efficiency of flow should increase substantially. With this long of a run, you may have to buy and install a more powerful exhaust unit as well. You won't know this until you do everything you can to improve the flow and then observe the performance of your finished product.
As for the insulation…..it's purpose isn't to keep the duct warm at all times, but to allow warming of the duct while the warm room air moves thru it thus eliminating condensation and the resulting "drip-back". Without any insulation, the heat that the exhaust air contains is rapdily lost thru the thin skin of the duct and the air is chilled so rapidly that the contained moisture condenses out on the interior of the duct. In extremely cold winter climates such as ours, I'll usually wrap these ducts with spiral wound FG batts held in place with some lightweight wire or zip-ties rather than using thinner types of pre-formed pipe insulation. Whenever this has been done, we have no "drippers".
Your roof vent is supposed to have a flap door on it that closes when the fan isn't running. The exhaust unit itself should have flapper on it as well. Those dampers should prevent much outside air at all from entering the duct.
I'd recommend installing the rigid pipe and the insulation. Then turn the unit on and climb the roof to see if your unit has enough guts at this distance to open the roof vent flapper. If it can't, you need a more powerful exhaust unit or you need to find a way to make a shorter run to a suitable vent.
Knowledge is power, but only if applied in a timely fashion.
Edited 2/4/2004 9:06:37 PM ET by GOLDHILLER
Thanks for the insight. Now, one more question. Am I supposed to have a vent through the roof? The flex pipe terminates under a square roof vent.
I have a steel roof (hard to walk on without damage) at 12/12 pitch (just hard to walk on). I don't feel comfortable 35 feet in the air to inspect a pipe.
Others have suggested a vent through a side wall. that would be a much shorter distance 8 - 10' vs 16+. I'm not sure I want to tackle installing a pipe through the roof.
Would you have additional thoughts?
Thanks, Eric.
Hovering the end of a duct near a roof vent is just hoping for the best, not guaranteeing it.
Despite that, terminating at a vent pipe is, I understand, allowed in some locales. It's still not a good practice in my estimation and experience.
The best way to assure that all that moisture is going outside where you want it, is to attach the vent duct to a proper roof or wall vent made for this purpose. If you have a suitable place to terminate a shorter run to a wall discharge, that should work fine, too. You'd want to avoid being too close to a soffit vent or to a window, for example.
If memory serves at the moment, every 90 degree elbow you use in the line is equivalent to ten feet of straight run, a 45 equals 5'. Do your math as you lay out the difference between the two proposed vent locations and it should help you decide which is apt to be the most efficient.
Knowledge is power, but only if applied in a timely fashion.
Many advocate insulating deeply around these fans and insulating the sections immediately after the fan where the duct rises. Ideally the duct then heads down hill uninsulated, some advocate substituting a PVC pipe for the flexible duct for these sections as it better assures a nice and leakproof slope, and out of the building.
Idea being that the condensation that occurs on the down slope goes out the vent and the insulation keeps the fan housing and the beginning of the ducting close enough to the inside temperature to prevent condensation on these surfaces.
The fan box is surrounded by fibergalss insulation. The pipes are uninsulated flex pipes that exit the fan and bend straight up about 16 feet through an uninsulated walk up attic. Your 'downhill' comment make me think the vent should exit the house near the soffit? Should they be vented differently?
Thanks, Eric
Does this happen only after the fan is used, or whenever it's cold even if the fan hasn't been running? Is moist, warm indoor air leaking up there and condensing in the duct without the help of the fan?
In either case, it sounds like 16 feet of uninsulted duct provides plenty of cold surface for water to condense on. A shorter run, especially if it is level or pitched away from the bathroom should help. Insulation can't hurt either, but I wonder if insulation alone would be enough in this situation.
Al Mollitor, Sharon MA
Whether or not the bath is used or the fan is run. I think it most likely the warm moist coming in contact with the cold fan.
Would you think a low end fan is powerful enough to push that amount of air?
I don't have gable end close enough, and the ridge vent is just so far away. I have an walk up attic to pass through before I can vent.
Thanks for the comments.
Eric, KC.
I run the duct with a down slope to a gable wall, vented to outside. But I also insulate the entire hose, as well.
There's conflicting opinion as to whether or not directing the hose at a ridge vent or gable vent is adequate; in my experiance I've seen dripping exhaust fans whose hoses were hung near vents, so I direct mine outside, either thru gable wall or out the roof. Don't exhaust out the soffit, if you can avoid it. If you have soffit vents, the moist air will draft up into the attic, causing more problems.
I never met a tool I didn't like!
I took another look at where I might vent and it looks like I have a small wall area where the garage roof level is lower than the main roof, about 10 - 12' feet away. Would that be a good option? If I punch though the siding, would I use a dryer vent cover for this as well? To facilitate draining, would I use a smooth pipe like pvc? What type of insulation?
Thanks, Eric - KC
i had this problem last yeat. it is cause bt the cold air in the attic condesning with the uninsulated pipe. I slip some insultlated HVAC flex duct over my pipe and it solve the problem. I also had it exit under the ridge vent. It coated my plywood with mold. I had to exit through the roof.
Question: have anybody seen those PVC vent caps for fan exit. Its like a six in cap that screwed to the three inch pipe to keep rain out. I cannot find any here.
It sounds as though the wall would work to vent thru (if I have the correct visual picture of what you describe.) Go to the home center or hardware store, they should have everything you need. Solid PVC can be used, but it is harder to work with unless you cut it short and connect the ends using flex duct. I often use the 4" dryer expandable aluminum duct as a good substitute, especially if the run is fairly short. Keep the run straight and as short as possible. You can cut thru the siding using a jig saw, even a keyhole saw, but I prefer a 4" holesaw for a clean cut.
For wooden siding, I use a Fein Multimaster to cut a square down to the sheathing, flash it, run a bead of caulk around the opening, nail in a block, then use the hole saw to cut the hole, viola, instant trim.
Use fiberglass for insulation. Around here they make 1" FG insulation for garage doors. I cut it into strips, wrap it around the duct and tape it on.
Use a plastic bird cage to keep the critters out, and I often use a second damper near the wall in the duct to minimize cold backflow in the winter. (Also, the shutter-type of vent head is made of plastic and over time exposure can warp one or more blades, causing the shutters not to close. With an in-line damper, this isn't a big deal.)
Good luck.I never met a tool I didn't like!
The 16' vertical run is the problem. The water is probably condensing near the top and dripping all the way back down. If at all possible re-route it through a sidewall with a short run of pipe and run as much horizontally or slightly downhill as possible.
There are a lot of knowledgeable people who say that venting out the soffet is a poor choice. The general line of reasoning being that in a soffet vented building the moist air could be drawn into the attic space and condense on the inside of the roof deck. If this were to happen it would be bad.
I contend that the warm moist air exiting a vent at the soffet, in any exterior temperature that interior icing or condensation is a problem, would immediately cool, cross the dew line and drop its moisture.
This would occur so fast that the slow air movements into a typical soffet, particularly if you vent on the lee side of the house, would have little chance of drawing the exhausted air in before it cooled to near the ambient temperature and the moisture fell out. Once the air is close to the outside air temperature it would be no more of an issue than the rest of the exterior air.
IMHO, the only real danger that venting through the soffet might pose is that the wall directly below might become covered with ice. Some advocate venting through the roof but if the roof is covered by two feet of snow this might be more of a trick than originally planned.
I'm getting a lot of good comments. seems like keeping the pipe as warm as possible for as long as possible may be the answer. My down stairs vents are fine, as the travel through heated space first. Since I have a long distance to travel through unheated space seems to be my problem. Eventually I will finish the attic so I will have a heated space, I'm not to that point yet.
Someone else suggested exiting through a wall might be an option, and it would be 1/3 the distance. Could I run into moisture on the wall issues?
In Kansas City, we have a lot of cold and not the extended snow covering. The air is usually quite dry in the winter here. I've had to run a humidifier to keep down the static and our skin from drying out. It may be adding to my problem, I'd hate to give it up.
Thanks, Eric
"In Kansas City ...... not the extended snow covering."
WHAT, WHAT, WHAT!!!!!!!!!
It is all of your fault.
The problem with sidewall venting is that if it is right under the soffit vents it will suck that moisture back into the atic and condense there.
If you have a gable end you can exit there.
As far as venting just under the ridge vent Bob Walker says that he sees it in Toledo and it usually works.
BUt with all of the metal it is less likely to work. In the winter. Also with the humidity in the summer you might have a problem. Brownbag said that it did not work in his house down on the Gulf.
Bill, by Lake Tapawingo -- at least I think that there is a lake out there SOMEWHERE!
Well, here it is Feb 5 and we have our first major snow fall of the season. It snowed a few times this season, an inch or two here, an inch or two there. Not much to write home about. Usually gone in a few days. We got 7 - 8" today. the most I can remember in a few years. Ice is more of a problem. I also remember some years cutting grass the first of March, so this is cold late this year.
I do have an option of venting on a gable end in a space over the garage roof and under the main roof, so there is not a problem with soffit vents.
I did some surfing for side wall vents. Most sites recommend dryer vent that double as bathroom fan vents. I did see something interesting. there are special soffit vents that connect to the vent pipe and exit the soffit between the regular soffit vents. What would be your opinion on something like that? Still a problem with getting moisture sucked back up into the attic?
Thanks, Eric.
P.S. Maybe you get the lake effect snows like I remember growing up in Buffalo ;-)
"I did see something interesting. there are special soffit vents that connect to the vent pipe and exit the soffit between the regular soffit vents. What would be your opinion on something like that? Still a problem with getting moisture sucked back up into the attic?"
I don't know of any rule of thumb of distance, but with the normal space on soffit vents I am afraid that is what would happen.
So, what does one do for venting where snow is measured in feet on the roof?
A long pipe like a vent stack? The roof-wart jobs would seem to be leaky and non-venting.