Bathroom Vent - Soffit Vent

[daveswoodhauler]

Ok, getting rid of the load builder special (chitty) bathroom fan/light combo in the bathroom that cannot even suck/hold in place a small sheet of 1 ply toilet tissue.
Went out and got a 140 cfm fan/light kit at 2.0 sones.....needed something quieter/more powerful to take out the steam after the Mrs's showers that last 30 minutes @ 135 degrees (just kiddin love)
Anyway, the current setup is that the vent tubing is just vented into the soffit....but the problem I think is that the holes in the soffit are very small, and I think this hampers the ability to blow the moist air out the soffit.
The old fan unit is a 4" duct, and the new one takes a 6" line, so I wanted to put some sort of vent in the soffit so the exhaust is vented outside.
I guess I was thinking of installing something like the vent that we use for our dryer vent...this vent basically opens when the dryer is on, and then closes when the exhaust is done.
Problem I am thinking if I use the same approach on the soffit, the soffit faces downward, and I don't want cold air coming into the fan/tubing then into the bathroom. (The fan/light kit I bought has a sort of flap in the unit, but it doesn't seem to seal very well when the fan is not on)...I was thinking one of the roof vents perhaps, but we are in New England, and the vent would be on the North/West side of the house)
Also, my soffit seems to be in sections of perhaps 18-24 inches, do they just snap apart?...I'll try to post some pics tomorrow.
Any suggestions?

 

[Tarmsolo60]

I just installed the UEV 4 in my soffit to shorten a long run to the gable end of my house which restricted my fan. I'm still deciding if I'm happy with it as it's all plastic, but it's all I could find. It does have backdraft dampers on it. It says it's good for up to 5".

(broken link removed to http://www.fantech.net/accessories4.htm)

 

[velvetfoot]

This is what I installed for my bathrooms:
(broken link removed to http://www.hardwareandtools.com/invt/9261165)
I couldn't find anything else like it that was better.
They're 4".

I took out the dampers in the fans to lower back pressure, but I don't know how it will work in the winter yet.
The damper in the vent isn't exactly air tight or anything.

The old vent did not have a damper but it had a screen that was very clogged up with lint-like a dryer. Must be over the years it collected from towels, etc.

 

[fbelec]

being a electrician i install alot of fans. no matter what you have to prevent air backup into the house it will happen. that soffit vent that velvetfoot used is something i have never seen. that looks nice. what i have used is a dryer vent type. as long as you keep the vent level the flap stays closed. in soffits that are wood or plastic i've installed the vent using screws and strapping to have the vent be level and shooting the air down or just rely on the flapper on the fan and install a round metal soffit vent and hook the flexible vent pipe to the 6 inch round vent that has a built in bug screen. if i use the dryer vent type i put a piece of coarse screen, chicken wire or buy the dryer vent with built in plastic screen. the roof vents are nothing but a dryer vent with a bigger foot to fit under the shingles. they work ok on large fans but not so good on small ones. you have a very large fan if it's in a fairly small bathroom it will pull so much air out of the bathroom that when you get out of the shower you'll feel cold. with a 6 inch vent 2 sone is not that quiet. if your willing to run a 6 inch vent you could get a fan with .9 sones. really nice. once you step up over 110 cfm the vent goes from 4 inch to 6 inch but also with the larger vent it gets quieter. if you take your vent straight out to the soffit insulate the vent line and tip it so that any moisture will run outside and not sit in the house and leak. the insulation over the vent line will help with the condensation build up

 

[velvetfoot]

I was able to just put the line in a rafter bay with the attic insulation over it. It was a very short run.
It's at the edge of the soffit so it shoots it out there.
I have a nice dryer vent with a positive seal but I couldn't find a soffit vent like that.
Then again, the dryer outlet has a lot more 'ooomph' than a 90 cfm bath fan, so the vent can't be that substantial.
I tried the fan with both dampers in place and there definitely made more noise (back pressure), so that's why I'm trying just the outside vent.

 

[coolidge]

Every house is different for venting so use your best judgment, if possible use a six inch smooth bore pipe for optimal performance.A flex pipe cuts your total cfm in half. Do a google search for Panasonic whisper quiet fans, these things are nice, can barely hear them.

 

[LLigetfa]

My dryer vent has a double damper to prevent backdrafting. Venting into the soffit area is a bad idea as that is normally the intake for the roof venting system and the updraft will carry the moisture into the attic. If you go through the soffit with enough velocity it would probably be fine. I don't have individual exhaust fans.

I have a central HRV that draws air out of the bathrooms, kitchen, laundry, and crawlspace. One regret I have is that I didn't vent the range hood but rather recirc through a carbon filter.

 

[velvetfoot]

With the bathrooms on the second floor I think I'm more concerned about out-venting (stack effect). I don't know if there's enough pressure on the outside vent damper - I don't know how much the stack effect is good for. They can't be too heavy (as I was saying about using the fan damper as well) for back pressure on the weaker fan. I guess I'll observe during the winter - maybe the thermometer gun can sense a temp change. Of course, I don't know how I'd get a reading, leaning out the window and all would skew the results. Maybe just see if the flapper moves.

 

[daveswoodhauler]

Thanks for all the responses.
I agree that 2 sones is not too quiet, but will be a big difference from the 3.5-4.0 one we have now.
Right now, the vent pipe just sticks into the soffit area, and has been that way for 10 years and there is no mold at all.
The bathroom is about 10X10 with 8' ceilings, so I think that 140 cfm should be ok.
I think I am just going to go with a round soffit vent and see how the flapper works on the fan....if I seem to be getting a lot of air coming in, I'll try a vent with a flapper like on my dryer vent.
I am using some semi rigid aluminum duct work, as I figured that was better than the really flimsy flexible stuff....would think that the rigid would allow more air flow. I'll try to take a few pics today and let you know how the install goes tomorrow.
Thanks folks!

 

[velvetfoot]

I installed a new fan in place of an old one as well and thought the same thing. I would not sell that plastic flex stuff short, at least compared with that aluminum flex stuff. I tried to go into the attic as little as possible (it was summer). I tried to pull that aluminum flex stuff in a short run over to the soffit to replace the existing plastic flex stuff, and let me tell you, it tears very easily. The plastic stuff is quite rugged in comparison. Anyway, as LLigetfa has said before, if the bathroom is on the second floor, the problem could be the air exiting, and the temp wouldn't be cold; you'd have to use smoke from an incense stick or something to test (which I have yet to do upstairs anywhere).

 

[daveswoodhauler]

I installed a new fan in place of an old one as well and thought the same thing. I would not sell that plastic flex stuff short, at least compared with that aluminum flex stuff. I tried to go into the attic as little as possible (it was summer). I tried to pull that aluminum flex stuff in a short run over to the soffit to replace the existing plastic flex stuff, and let me tell you, it tears very easily. The plastic stuff is quite rugged in comparison. Anyway, as LLigetfa has said before, if the bathroom is on the second floor, the problem could be the air exiting, and the temp wouldn't be cold; you'd have to use smoke from an incense stick or something to test (which I have yet to do upstairs anywhere).

The duct piping that I am using is a more rigid type than the slinky type stuff that bends when you pick it up. If the stuff I have tears easy, thanks for the warning about it tearing. Its a pretty short run....straight off thefan unit for about 4-5 feet, then a quick 90 degree down into the soffit.

 

[velvetfoot]

As I recall it was the ovalizing and pulling through that last section that got it. It really tore easy. It sounds like the same stuff. I still managed to do most of it from below, which is not as much a factor this time of year.

 

[daveswoodhauler]

I think the stuff I have should work ok....I can do all the work from the attic thats wide open, so I have plenty of room.
Thanks.

 

[fbelec]

the flex isn't bad, you just can't use alot of it. that stuff is made just to hookup the fan to dryer vent or smoke pipe. i've run the 4 inch smoke pipe from fan area to gable end of the house and it works great. 2 feet of flex to hook them together straight shot out. no bends. i've done 22 foot run and work like mad and it cut down the noise a touch. people have the bad habit of trying to run twenty feet of flex and wonder why the bath is molding. or 8 foot run and use 2 sections of flex and not cut the excess off which make the 2 sone fan push 3 sone sound

 

[Highbeam]

On the sound issue, you don't want it too quiet. That sound is cover noise for major colon blows. Your wife will thank you for a little noise here.

50 cfm is the normal bath fan for a normal 50 SF bathroom. 1 CFM may not be code but it is standard. You describe a 10x10 room so the 110 CFM fan is just right.

On the fan switch, consider installing the cool timer switches that remain on for 15 minutes or more even after you turn the switch off. You need to run the fan for longer than the time that you are making steam. If you can install a fan, you can replace this switch.

On the duct I have the preinsulated plastic duct work made for this job and I hope it works. I use the roof vents since I can then minimize the run length. The roof vents are easy to cut into an existing roof and they include a flapper and bug screen. You want the duct run insulated so that the steam doesn't condense in the duct and then run back into the fan where it will drip onto the floor.