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Old 04-29-2020, 06:14 PM   #1
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Best option to increase Bathroom Ventilation?


I am looking for advice on how to add adequate ventilation into an open floor plan style of bathroom. The house is about 30 years old and there is a 50 CFM fan in the tiny "closet like" room which contains the toilet bowl. That is enough ventilation for the toilet but not for the shower and bathroom. I have attached a couple of pictures so that it is easier to communicate and ask about my situation. The first photo shows the existing fan in the small room. The second photo shows the shower and open floor plan. I have tried to think about my options, most of which are numbered in red in the photo.

My initial thought (option #1) was to install an inline fan in the small cavity over the ceiling above the toilet. Then add a second duct to pull air from the open bathroom, a duct on the wall above the door as shown in the photo or along the narrow wall which faces the tub. That seemed like the easiest option but then I realized the exhaust duct (see addendum) through the roof may need to be a larger diameter. And one will need to flip a switch by the toilet before taking a shower, which might work but certainly not how anyone would design things up front.

My second thought (option #2) was to replace the shower down light with a combined light/fan in order to have them on the same circuit and better insure that the fan runs along with the shower. But after some causal browsing it appears most of these combined fan+light do not draw enough CFM for the space. I am also concerned there may not be enough space for the fan mechanicals in the shallow overhead roof space, and about the exhaust vent being too close the the skylight. (I recently installed a Velux flashing kit to fix the leak which can still be seen in the photo. So I thought now was a good time to fix this ventilation problem before fixing all the cosmetic issues with the ceiling and wallpaper.)

(option #3) So then I thought I should cut a hole through the exterior wall and mount a fan on the interior wall. The house is brick veneer and I am a little hesitant to drill a whole through the wall which also contains a plumbing vent. Then there would be problem of running power to the fan without tearing out sheetrock and installing a new switch box. This would appear to be the most expensive and time consuming option. Also would having a fan motor so close to the shower be an issue with building codes and future inspections?

(option #4) is not shown, is to add a dehumidifier to control the moisture in the bathroom/house.

Addendum
--------
As I researched options I started thinking that doing a hybrid of #1 + #4, of adding a dehumidifier and potentially installing a larger/quieter bathroom fan could be an effective and low cost approach. Replacing the old "NuTone 696N B" with something like the "NuTone 110 CFM" to get a little more airflow. That set off a chain of events where I discovered that the old fan housing box was installed before the sheetrock, maybe not a big deal if I were careful about how I cut the new hole to gain access to taking out the old metal box. But then discovered that not only is the exhaust vent only 3" in diameter but the duct exit was installed in the soffit. I understand that is a bad idea, since the moist air will just be drawn back under the roof. Since fixing the incorrect venting will require cutting a larger hole in the ceiling to get enough access to reroute the exhaust vent I am back to thinking that option #1 is worth considering.

I appreciate feedback from people who have dealt with this type of situation before.
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Old 04-29-2020, 06:32 PM   #2
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Re: Best option to increase Bathroom Ventilation?


#1 use the attic space above the toilet for a second fan.
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Old 04-30-2020, 09:27 AM   #3
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Re: Best option to increase Bathroom Ventilation?


Air exchange is what you want. Pressure needs to be equal.

A fan will efficiently pull air out but really it is pulling air through.

Most non-open bathrooms have a window. To pull air out means pulling outside air through bathroom, taking heavy condensation air with it.

Perhaps skylight that opens was meant to achieve that air supply?
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Old 04-30-2020, 12:26 PM   #4
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Re: Best option to increase Bathroom Ventilation?


If the room is under negative pressure, drier air will naturally leak in.

Just put a second exhaust fan.

50 cfm is the minimum and I would go higher. Just keep in mind the fan must be vented to the roof and the duct must be properly sized.
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Old 04-30-2020, 05:12 PM   #5
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Re: Best option to increase Bathroom Ventilation?


I'm thinking with the entire upper wall open to the bedroom, any fan where you can live with the CFM noise won't do a whole lot unless it's right near/over the shower.
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Old 04-30-2020, 10:30 PM   #6
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Re: Best option to increase Bathroom Ventilation?


How large is the bathroom you are trying to ventilate?
An 8 X 8 X 8 room is 512 cu. ft..
Your fan can easily change the air in a little over 10 minutes.
Perhaps you haven't got enough air infiltration for it to do so.
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Old 04-30-2020, 10:43 PM   #7
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Re: Best option to increase Bathroom Ventilation?


take the wall out between the toilet and the rest of the bath. The room will feel larger and less constricting. Then, put in a larger fan
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Old 05-01-2020, 12:20 PM   #8
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Re: Best option to increase Bathroom Ventilation?


Wiser to wall off the bedroom to contain the moisture.
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Old 05-04-2020, 07:17 PM   #9
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Re: Best option to increase Bathroom Ventilation?


Thanks for all the comments and suggestions. After considering your feedback and thinking about it more, I plan to do something close to option #1. But rather than install an inline fan to service both the shower and toilet, I will add a second, more powerful CFM fan in the ceiling cavity above the toilet. I believe that is the best balance of effectiveness and cost. (I do not want to remodel the bathroom or bedroom to address this problem). I will make the final decision once I open up the sidewall or ceiling to inspect things more closely.

It was not visible in the photos that I posted but there is second skylight in parallel with the existing toilet vent fan but about 1 foot higher up on the roof face. I think there will be just enough room to install a couple of roof vent caps below the skylight, being careful not to get them too close to the corner of the skylight (as a lot of water gets diverted around the corner of the skylight during a heavy thunderstorm).

That fan location will also make it easier to get power, either by installing another switch in the toilet stall or maybe just borrow the existing fan circuit and tie the existing fan and toilet light together off the same switch. In either case I may add a wireless switch near the shower as the main fan control.
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Old 05-07-2020, 07:37 PM   #10
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Re: Best option to increase Bathroom Ventilation?


After cutting a hole above the toilet door I am posting a couple of photos for those who might be curious what it looks like inside the small ceiling cavity. Next I will need to decide on a specific fan and where to place it. There is not much room but something should be workable.

I am curious about the black deposit on the electrical cable (below tape measure). The cable is very dark right where the cable changes direction after running up the wall before traveling over to reach the light and fan. While there are signs of some mildew on the vapor barrier it is dry inside and the wood looks pretty good. Maybe it is cooler at that spot in the summer because of the air conditioning in the space below and the thermal conductivity of the cable, causing water to condense at that spot?
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