Bathroom vent

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Posted by: from Ottawa
11/19/2012 at 7:49:33 PM

One of my upstairs bathroom fans was not clearing out the steam so I took a look into it. Fan seems to be ok as it operates at about the same speed as the other similar fans in our house. Then I found out that the vent pipe on the fan is 3" but I could see down most of the inside it and it is clear.

As I followed the pipe I realized that it was being vented out the soffit as is the other upstairs bathroom vent that is working fine. The exit on the soffit vents is a round 3" exit with very small slits in it. I can hear a slight high pitched whistling which sounds to me like air restriction. I assume the small slits are clogged.

The vent pipe itself is covered in insulation for the first 3 feet and then the last 2 feet it is outside of the insulation as it drops down to the soffit. Maybe this is key as it allows the air to cool a bit before exiting and maybe reduce and chance it rises back in via the slits in the soffit. Any moisture than condenses in the vent pipe runs downhill to the soffit exit.

The house was built in 1989, so 33 years ago and in the upstairs bathroom that is working ok with the same setup of fan, vent pipe and vent, I can see easily from above that there is no mold at all on the insulation or wood above in the attic on this working one so I'd assume the other one is most likely the same given that we use the working bathroom more.

My question is:

Regardless of whether I upgrade the fans, should I just find a newer version of the soffit vent and assume I won't have any problems as it has worked fine the past 33 years? I would assume so.

Secondly, If not should I vent up through the roof which for me is not a DIY project?

Thanks for your help,


bathroom vent
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Date/Time11/19/2012 at 9:28:41 PM

You have to clean the went pipe or you have to replace the pipe.

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Date/Time11/19/2012 at 9:41:01 PM

Hi Ed

When we are installing vents in bathrooms today we use fans with a rating of at least 110 cfm ($ 200.00 +) or larger which require 4-5" pipes. A 3'' vent and a 50 cfm fan ( $20.00 ) will not evacuate any serious moisture especially in days of tighter homes.

Soffit ventilation is ok as long as you are diligent in insulating the solid vent pipe well (not plastic) in the attic. I have seen 2' foot icicles hanging of f UN or poorly insulated pipe in attics (condensation) That melts and soaks the insulation or worse. Ceiling fans were never intended to be HRV systems.

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Date/Time11/19/2012 at 9:49:25 PM

I would start by checking the sofit vent to see if it's actually blocked. The design of it sounds restrictive, so it would be better to replace it. However sofit vents are not ideal as they can allow the moisture back into the attic. A roof vent is better and not really that hard to install.

When looking for a new fan, the more CFM the better and look for a quiet model with a low sone rating. Panasonics whisper series are very good and are easy to install in retrofit situations, unlike most.

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Date/Time11/19/2012 at 9:56:52 PM

Hi ed,

like one of the other posters stated,3inch diameter ductwork on small cfm fans will not effectively ventilate your bathroom. we have used for some time now panasonic fans, they are in my opinion an excellent product and a 150cfm fan requires a 6"dia duct and is super quiet too, we vent them out the roof using insulated ductwork (steel) through the attic space, panasonic also mfrs a 110 cfm fan that requires 4inch ducting but again each bend in the ductwork restricts airflow by 5% so minimize bends,

the steel roofvents by broan are a good choice,you can hire a roofer to go up on your roof to install the vent which you can supply,they will charge you approx$65-100 dollars depending on the slope of your roof and the time of year too.

We seldom ever use soffit venting for bathroom fans as it does not work as efficiently as a rooftop or gable-end vent, the key thing is to make sure the insulation extends to the exit point.

Fyi, the panasonic fans also have built-in backdraft dampers to keep cold air from backdrafting down into bathroom.

Good luck.

Bob Beal

Artisan Bathrooms


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Ed in Ottawa
Date/Time11/20/2012 at 12:12:32 AM

Thanks all for your help. I'll go the roof option as that was my original thought anyways. Was a bit surprised that it was in the soffit to start with.

I've checked out the broan roof vent. Looks good but is it too low during snow build-up in the winter?

Have found another one, not all that pretty, but I'm sure it will work. Anyone had any experience with it?

It's the Maximum CT-4

Bathroom vent
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Date/Time11/20/2012 at 7:45:29 AM

Hello Ed,

This is a common problem that I see all the time. Years ago a piece of plastic duct was acceptable for exhausting a bathroom. Current building codes require any duct passing through un-heated space to be insulated with a vapour barrier. This will prevent warm moist air from condensation in your duct as it passes through attic.

Ideally it would be better to vent through roof. If using soffit I would ensure that your louvers are at least pointed away from house so that the warm air does not rise right back into your attic through your vented soffit. I see a lot of mould in attics from bathroom exhausts that are vented in soffit. I believe I read somewhere when you do exhaust out a soffit it is required to be un-vented on each side to prevent moisture air from rising into attic.

The best solution is to replace exhaust duct with proper insulated duct and then vent directly through roof. What ever you decide is based on how much you want to compromise quality for expense and effort :)


Roger Frost

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Ed in Ottawa
Date/Time11/20/2012 at 11:05:45 AM

Thanks Roger,

Took a quick drive around my neighbourhood today. I don't see even one house that has vented via the roof. That surprises me as I'm sure some have upgraded their bathrooms by now and 3" vent size is not all that large for some of the bathrooms in the homes in our neighbourhood. Most would need 110 CFM minimum (as that is about the size of most master ensuites (100 - 120 sq. ft, 8 ' ceilings)) which needs 4" vent pretty well to keep up the flow.

Secondly, I did go back up in the attic and here is what I found. Batts insulation is installed all around the outside of the attic at 45 degrees and or vertical; basically ceiling off all the soffit ventilation. Then there are in numerous places where there are the air baffles added to allow air above the insulation from above the soffit. Not sure if that makes any difference but appears to only allow certain areas to suck in ventilation air. None of these areas are near (within 5 or 6 feet of) the two bathroom soffit exhaust vents.

Again no mold anywhere. If it ain't wondering if I'm missing something that everyone in the neighbourhood realizes.

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Date/Time11/20/2012 at 12:01:12 PM

Hi Ed

Three inch ductwork is fine. Start by replacing the round 3 inch vent that exits the soffitt with one that is not as restrictive. If that doesn't fix the problem you may have a weak fan that needs replacing.

Ignore all of the advice given above.

Dan Brown, RHI

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Ed in Ottawa
Date/Time11/20/2012 at 12:08:37 PM

Now I'm confused. This is what I don't want to happen.

Bathroom vent
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Ed in Ottawa
Date/Time11/20/2012 at 12:12:02 PM

Instead, here's a link to the photos:

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Ed in Ottawa
Date/Time11/20/2012 at 12:33:19 PM

So I got off the soffit vent and it was not plugged at all, maybe 10% at most. Ran fan with no vent cover on it and it still did not clear the steam from the bathroom so....thought it might not have enough air supply so I opened the bathroom door. Did help a bit but still fogged up mirrors in the 8 x 7 bathroom.

Not sure why this one does not work and the one in the master ensuite is fine and that bathroom is 10' x 10' with same fan, vent pipe and soffit vent. Hmmm.

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Peter from Services Plus in Innisfil
Date/Time11/20/2012 at 3:17:44 PM

Thank you for your inquiry. I would agree that you should probably update the fans and soffit vent. However we do not specialize in this area. You should look for a handy person who has done this sort of work before. We are more specialized in heating, air conditioners and gas appliances.

Thank you,


Services Plus


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Ed in Ottawa
Date/Time11/21/2012 at 1:10:28 PM

Looks like roof vent will definitely work at a cost to just cut the hole and install the roof vent of $400 for the 2 bathrooms. Cannot get anyone at this time to do the work until the spring as winter is coming and they are already booked pretty well for the next few weeks.


Upsize the soffit vent and hope for the best. Cost for new soffit vents $40. 23 years of experience with the installation has to mean something. If shows signs of not working then add roof vent later on.

Problem is that accessing the second bathroom requires crawling around up and under rafters to get to it. About 20 minutes from attic hole to far side of roof. Moving boards across the rafters as I go. So changes and even observing it take lots of time and when you forget your's 40 minutes to go and get it.

So maybe wait to spring and go the roof vent route.

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Date/Time11/27/2012 at 6:01:56 PM

Hello Ed,

I've handled this type of problem in the past. As a matter of fact, I saw the exact same soot like material

on a home exterior in Hunt Club Woods in Ottawa. Their problem, like yours involves both the fan, size of pipes, exterior vent, and the volume of space being vented. We can build a new vent for you through the roof or through the Soffit and also upgrade the bathroom fan to a more powerful unit to speed up the removal of the humidity.

Another option is a humidity control (humidstat) that automatically monitors and expunges the moisture. As well, your air balance available to this area should be measured to permanently correct your problems.

Good Luck


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Ed in Ottawa
Date/Time11/27/2012 at 7:16:08 PM

Thanks Norm.

All I'm concerned about is whether expelling through the soffit is an option. That is what is there now but the vent in the soffit it way too small. I don't have any "soot" as you call it but am concerned that if I up the airflow out the soffit that it will increase.

Anyways, you mention that you can upgrade the soffit vent, can you tell me or give me a link to what you might use there?

I was going to use this as an attempt with a 4" exhaust pipe. It says it can do 6" but when I saw it at HD it is a bit restrictive at the self-closing valve for the flow of 6" pipe.

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Ed in Ottawa
Date/Time12/13/2012 at 3:51:19 PM

So here's a picture of the new vent. Compare the size to that on my first post which is the original vent.

Bathroom vent
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Ed in Ottawa
Date/Time12/13/2012 at 3:56:39 PM

Here's the old fan and venting. The part straight out from the fan had loose insulation covering it but the part that curves was up outside of the insulation.

Bathroom vent
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Ed in Ottawa
Date/Time12/13/2012 at 3:57:52 PM

And here's the new one.

Bathroom vent

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