Vent bath fan to soffit vs. side vs. roof

[newowner]

I live in central Maryland in a house built in 1981. The master bath on the 2nd floor has a window and no exhaust fan. It shares a wall with a full bath that has an exhaust fan that (I think) is vented by a duct that is under the attic insulation and runs to a soffitt vent under the roof overhang. For sure it doesn't vent through the roof or the side of the house. I am pregnant, so I don't want to crawl around the attic so I am going to have my husband check this exhaust fan's venting tonight when he gets home from work or tomorrow morning.

Anyway, I am having an electrician install some overhead lights in the 2nd floor bedrooms and thought I'd have his crew install an exhaust fan in the master bath while they were here but I am confused about the best way to vent the exhaust. The electrician is an expert in electricity, not venting. He said he could run the duct to the side of our house, which would be 22-23 feet of ducting. Going out the front of our house would only be about 2 feet because the master bath is in the front of the house, but who wants to look at a vent cover on the front of our siding!! I haven't asked the electrician if his crew knows how to vent it out the roof using a roof vent cap. My husband was thinking he could maybe try the roof vent if they say they don't have experience with it, but he is not much of a handyman with no experience of this either, so I am worried about that.

My research indicates people are divided on if venting to the soffit vents under our roof is a good way to vent or not. I got quotes from 2 electricians on my work, and one said soffitt venting is o.k. for central Maryland and the other said he thought some of the moist air would come back in through the soffit intake vents and cracks and gaps in the soffit materials, etc, and cause mold in the attic. The internet has people saying yes it is fine and others saying no, it is not good. Of course it would be the easiest way to vent.

So what do you all of you think? If it truly is not a good idea to soffit vent, then I am wondering if I should change the hallway bath fan so it vents out the roof or side also. If so, since the baths share a wall I could buy a Fantech inline fan system. But should we vent out the side, which would be 22-23 feet or to the roof, which would place a roof vent cap on the front slope of our roof, very near the pipe that is on the front slope of our roof which I think is the pipe that vents out the sewer gas. I don't even know if it is safe to cut a hole near that vent pipe besides the fact we then have two ugly things on our roof to be seen from the front of our house. Please share your thoughts and experience!

 

[Jadnashua]

I vented mine through the roof. You might also like the vent kit option as part of a tubular skylight. My bathroom (in a townhouse) doesn't have any windows, so adding the tubular skylight really helped. www.solatube.com. I don't like the idea of going through the soffit vents. In the winter, you are likely to get moisture into your insulation IMHO. A vent in the sidewall works fine, but most can't be painted to match without working hard at it, and looks is an issue (although you are probably the only one that will notice).

 

[Sponsor]

 

[TedL]

I moved into my current house, built 1985, six months ago. The master bath was "vented" into the area behind (above) the perfed soffit. The build-up of dust over the years has blocked the perforations, and there now appears to be some mold on the roof sheathing in that area. I'll deal with that as part of re-roofing this Spring.

I would not vent into the soffit area! There are vents made to be put into (actually through) the soffit. If the appearance doesn't work for you, consider going out the roof behind the peak. That's a long distance to the sidewall.

Also, consider using insulated ducting (about $20 for 25 ft of 4 inch at the big orange box). I've seen low spots accumulate moisture and freeze over in the dead of winter. Your winters are more moderate than ours, but still......

 

[newowner]

TedL-What concerns do you have about the long distance to the sidewall? Also, if I find the vents that actually go through the soffit vent do you think that is a good idea? I don't think appearance would matter because it would only be seen if you looked under the roof overhang. When you re-roof your house how are you planning on fixing your bathroom fan venting problem?

My husband likes the idea of rigid metal duct, instead of the flexible ducting that comes pre-insulated, so if we went with rigid ducting would we need to buy that foam spray insulation to coat the outside of the ducting?

 

[TedL]

TedL-What concerns do you have about the long distance to the sidewall? Also, if I find the vents that actually go through the soffit vent do you think that is a good idea? I don't think appearance would matter because it would only be seen if you looked under the roof overhang. When you re-roof your house how are you planning on fixing your bathroom fan venting problem?

My husband likes the idea of rigid metal duct, instead of the flexible ducting that comes pre-insulated, so if we went with rigid ducting would we need to buy that foam spray insulation to coat the outside of the ducting?

I plan to run out a sidewall, about 5 ft from one vent unit and under 10 from the other. The side of the house is screened from view by some large trees.

The soffit mount vents look to work the same/as well as sidewall or roof vents.
This is one example of what I'm referring to, but I've seen them in local big boxes (orange and /or blue).

http://www.hardwareandtools.com/invt/4859328

Long runs reduce air flow due to friction/resisance, and allow the exhaust to cool, contributing to a condensation/freezing problem in cold weather. Your area is warmer, so the concern may be lessened. (Our design temp is generally considered -10, but we can have a week or two every few years where night temps go to -20. You're a lot warmer.)

The flexible insulated duct, with the inner "tube" removed, will slip over rigid metal duct of the same size. That's what I'd use if you need it. Condensation is still a possibility, even if freezing isn't.

 

[newowner]

TedL-Are you going to connect your 2 ducts by a wye or are they going to go out separate sidewall vents? If so, are you using an inline fan that goes in the atttic while the bathroom ceilings just have grills in them or are you using two exhaust fans with ducting joined? Why did you decide not to use a soffit vent that actually goes through your soffit perforations?

 

[TedL]

TedL-Are you going to connect your 2 ducts by a wye or are they going to go out separate sidewall vents? If so, are you using an inline fan that goes in the atttic while the bathroom ceilings just have grills in them or are you using two exhaust fans with ducting joined? Why did you decide not to use a soffit vent that actually goes through your soffit perforations?

I'll be installing Panasonic heat/vent/light units to replace existing Nutone units. I did that in our first floor bath, and love the quiet of the Panasonic unit.

I'll run each line separately because:
I like the matching (white vinyl) wall vents available for 4", but haven't seen for larger.
It's easier.

I'm going out the side because:
It's easier to work there.
The side of the house is screened by trees, so it can't be seen except when standing near it.
I don't want the exhaust near the bath window.

In my previous home, I did switch two separate fascia vents into one 6" tee before going up and out the roof. Those baths (and old/new vents) were in the back of the house, and the switchover was done as part of my replacing the roof, windows, soffit, fascia & siding as one summerlong project. They worked fine.

 

[newowner]

TedL- thanks for all your info so far. My husband just checked our attic. The hallway bath is vented by uninsulated rigid metal ducting that is at about a 45 degree angle leading out to the back slope of our roof. He saw it by standing on the ladder and looking in the attic. I looked, too, and thought the ducting looked skinny-it doesn't look like 4" to me, but maybe fans in 1981took smaller ducting. So now we have to figure out a way to insulate it. Since it is already connected do you think spray on foam would be good?

The reason I was convinced it didn't vent to the roof was we don't have anything on the roof that looks like roof vent caps I have seen advertised. We have this square box on the roof with opening around the sides and I thought that was strictly for attic ventilation.

Do you think if we put a really high CFM fan in the master that it would overcome the air resistance problem of 23 feet of ducting? I ask because I am wondering if the soffit vents that cut through the soffit will clog up with dust like your perforations did. What do you think? Thanks for all your great opinions.

 

[Prashster]

If it were me, I'd use rigid pipe and make the run as straight as possible to the roof or side. Bends and flexible pipe greatly reduce the efficiency of the vent.

Check w yr local code to make sure it's ok to vent out the side wall.

I'd get someone to do the duct work if yr not that handy. Doing this right requires going on the roof or working on a ladder, cutting through the shell of your home, and patching/flashing so you don't get a water leak. I wouldn't want to screw with that unless I was confident about what I was doing.

 

[TedL]

Three inch vent pipe for bath vents was (is?) still quite common, particularly 25 years ago.

Insulation may not be the issue in your climate that it is in mine. If you have no indication of condensation in the current setup, you can probably forget about it.

The small holes of perfed soffit are clogs waiting to happen. The 4 inch opening of a vent isn't.

23 feet of aluminum duct isn't really that bad for a decent fan to push through, but check the manufacturer's installation instructions for any limits.

 

[newowner]

TedL- I could make the ducting "only" 18 feet by centering the fan in the bath, versus 21 feet if it were centered in front of the shower stall. I am going to look up some whisper series Panansonic fans and see what they say about max duct length. I eyeballed my soffit vents under my roof overhang and they only look about 4" wide and the soffit vents that go through are almost 7" wide so it looks like I can't vent that way.

As far as the existing fan goes, I guess I can't replace it with a better one if it is connected to 3" duct unless we make sure the hole to the roof will accommodate 4" duct. The existing fan motor still runs, so I guess that means I don't have to replace it, right?

Prashter, my husband will be happy when I tell him your info on rigid ducting. TedL-What kind of ducting are you going to use? If rigid, how will you insulate it?