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-   -   Bathroom exhaust... the ongoing saga... (http://www.diychatroom.com/f17/bathroom-exhaust-ongoing-saga-33795/)

landev 12-15-2008 03:18 PM

Bathroom exhaust... the ongoing saga...
 
Hi all,

I had a house built ~5 years ago on my property in N. Idaho. Initially, the exhaust vents for the bathrooms, kitchen, and laundry were located low on the metal roof. The first snowfall promptly ripped off 3 of the 4 vents. I had a roofer come and re-install the vents with some heavier grade vents, but last year these were completely ripped off. I spoke to a contractor and he suggested that I get rid of all the roof vents and exhaust the bath and laundry through PVC ducted to the ridge vent. When I asked about insulating the PVC, he said that would not be necessary.

All was fine and dandy until it began getting cold, then I had water flowing out of my fan fixtures due to condensation. I then insulated the PVC, but now that the weather has gotten cold, water continues to drip out of the fan fixtures.

The ducting currently runs 15+ feet through an uninsulated attic and up to the ridge vent for the bath/laundry at about a 22 degree angle. The kitchen vent is 6" and runs at a slight incline to a vent I installed under the eaves. None of the vents have flaps on the far side, as I could not locate such an item to install.

I have scoured the web trying to find an solution, I've spoken to contractors and building supply "experts"... no solution seems to be at hand.

As I have fought this for 5 years, :censored: I would like to end my continual trips to the attic, so am contemplating running to some soffit vents I would install under my porch ceiling. The actual soffit air intake vents are far out on the soffit, so I'm thinking that there would be little chance of the exhaust plume making it back into the attic via that route. The porch ceiling is oiled cedar, so I'm thinking it would handle the moisture fairly well.

Does anyone have any input that might be helpful? Am I on the right track in abandoning the long, steep angled attic runs of duct for a much shorter, more horizontal exhaust? Is there a better way?

Thanks in advance!

-l-

Termite 12-15-2008 05:04 PM

The more of the length of the fan vent that you can get running downhill, the better. Personally, I think venting to a ridge or roof vent and making long vertical runs is poor practice, for the exact reason you're having your problem.

Running the vent to a soffit vent will work ok in most cases. They do make soffit vent kits especially for venting bath fans, which makes a slick installation. Water dripping out of one of those would not do any damage to your soffit like a wet soffit vent might.

landev 12-15-2008 05:47 PM

Thanks for the speedy reply.

So, if I understand correctly, a soffit vent located on the porch should be fine? The distance between the porch vent location and the soffit intake vents is ~7'. I was thinking of locating the vent approximately 18" from the exterior wall... does this sound logical? Also, I thought of using a vent specifically for a 4" round duct (I believe this is what you referred to as being in a kit, correct?

I was thinking of connecting the existent 4" flex to a rigid 90, then go rigid to the outside location. I'm assuming this should all be insulated as well. There is also the option of going rigid the whole length, but that would require digging down through 30" of loose fiberglass insulation to get to the fixture... perhaps that would be the best route... what do you think, am I being too anal about this?

Also, I should mention that the 6" range hood duct is currently uninsulated. The cost of the insulation was quite expensive and I was told (probably incorrectly) that it was unnecessary. I should also mention that, so far, there has been no dripping from the range hood. When instructed as to how to vent the range, I was told to angle the duct slightly up to the outside under-eave vent. I specifically asked if this should be angled down (to allow for flow of water to the outside) but was told that it should be angled up rather than down to allow for a chimney effect. Any thoughts on this?

Thanks again!

-l-

Chemist1961 12-21-2008 03:32 PM

Venting Suggestion
 
Landev,
I too hate attics, but have been there running and repairing uninsulated central vac pipes. With no moisture intake in a system these pipes can still sweat and create blockage issues as well if uninsulated so your PVC problem is only multiplied by condensation. Just thnking out loud here. I believe our code in Ontario requires insulated flex exhaust for all new homes. Your vertical attic runs fight gravity so they should be minimised. Also check your fan dampers at each fan box on the next trip to the attic as I found one installed completeley backwards... with fan on it was blowing closed. I have bought and installed a pair of exhaust vents, heavy gauge steel, riveted, with felt cushion and washer weighted dampers for the outside and even my clothes dryer is warm inside now. Good luck

landev 12-22-2008 12:26 PM

Chemist1961,

Thanks for the input. I'm a bit hesitant to install much flex in the attic after having read a ditty about someone who contracted legionaire's disease from water that had collected in flex ducting. I'm sure this had to do with standing water in the ducting, so I imagine being diligent about having a clear downhill shot would have prevented that issue... it also seems that rigid ducting would have ensured a straight downhill run. I've also read that flex tends to collect condensation more readily than rigid... dunno...

One thing for sure that I've discovered... it's very difficult to find a contractor (at least in my area) who knows how to address this issue!

Thanks again for you advice!

-l-

duckdown 12-30-2008 11:13 AM

This feels like a poor job of providing proper insulation for the attic run.

Chemist1961 12-31-2008 06:42 AM

Good point from DD. Attic insulation should help the scenario. If you don't already have them installed, my energy audit also suggested timers for bathroom fans to be left running 20 minutes after showering, coupled with low flow shower heads hopefully producing less steam. I was in a new home's attic yesterday with insulated ducting and only the last few feet rise up at an angle to meet the roof vent. This attic was blown in level to R40 so all piping including the insulated exhaust ducting was fully coverred so in effect it had a double blanket..

wilsonfrench 01-05-2009 08:47 AM

Quote:

Originally Posted by Chemist1961 (Post 200974)
Landev,
I too hate attics, but have been there running and repairing uninsulated central vac pipes. With no moisture intake in a system these pipes can still sweat and create blockage issues as well if uninsulated so your PVC problem is only multiplied by condensation. Just thnking out loud here. I believe our code in Ontario requires insulated flex exhaust for all new homes. Your vertical attic runs fight gravity so they should be minimised. Also check your fan dampers at each fan box on the next trip to the attic as I found one installed completeley backwards... with fan on it was blowing closed. I have bought and installed a pair of exhaust vents, heavy gauge steel, riveted, with felt cushion and washer weighted dampers for the outside and even my clothes dryer is warm inside now. Good luck

...so let me understand this...I too vented my bathroom exhaust fan through my soffit...but my soffits are perforated...does that mean warm air is being sucked back into my attic?

Chemist1961 01-05-2009 07:07 PM

Wilson,
Your bath fan should be blowing to the soffit venting area and likely has a damper in line. My fan is a Nutone with damper at the fan box.I discovered this damper was mounted backwards. If you have no damper in line you can buy one at HD. It should be installed to tilt open when the fan blows, closed when fan is off preventing outside air from traveling into the bathroom, assuming you have atraditional bathroom fan set up.

I have also used an exhaust vent at the side of the house with a secondary damper, for my OTR Microwave. This is a weighted damper with a felt seal. Excellent item to prevent backdraft from a stickey hinge.

Your soffits are designed to allow air to flow up, through your attic to the roof top vents and work as part of a system. There is a correct ratio to create balance between soffit and rooftop. If I recall it is based on both area and pitch of the roof. Hope this helps

wilsonfrench 01-05-2009 08:49 PM

Quote:

Originally Posted by Chemist1961 (Post 207572)
Wilson,
Your bath fan should be blowing to the soffit venting area and likely has a damper in line. My fan is a Nutone with damper at the fan box.I discovered this damper was mounted backwards. If you have no damper in line you can buy one at HD. It should be installed to tilt open when the fan blows, closed when fan is off preventing outside air from traveling into the bathroom, assuming you have atraditional bathroom fan set up.

I have also used an exhaust vent at the side of the house with a secondary damper, for my OTR Microwave. This is a weighted damper with a felt seal. Excellent item to prevent backdraft from a stickey hinge.

Your soffits are designed to allow air to flow up, through your attic to the roof top vents and work as part of a system. There is a correct ratio to create balance between soffit and rooftop. If I recall it is based on both area and pitch of the roof. Hope this helps


Chemist...can one have too much air intake from the soffits? I have recently cleared my soffits as they had insulation (batts) covering them...can there be too much air getting into the attic? I have 7 roof vents and various baffles in my attic.
thanks


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