Bathroom Venting

[Paulski]

My bathroom is ~7x7 with the door/walk way in the middle, vanity & toilet on one wall, and shower on the opposite wall. I'm having a problem with mold and mildew on the top wall opposite of the shower head. After a shower, it's obvious thats where moister gets trapped. I currently have a vent/light combo in the center of the ceiling, so it's right outside the shower curtain (https://www.amazon.com/dp/B001PO29TA?tag=atomicindus08-20). I am thinking about adding another vent inside the shower area so the moister does trap in the corner of the ceiling. Since it will be right above the shower, I think I need to go with a remote exhaust fan. Seem like a good idea?
Can I run the inlet ducts so it ***** from the new vent above the shower and through he current vent, and out a single exhaust vent to outside?
Or should they have their own individual exhaust vents to the outside?
If individual, can the remote fan be mounted in the attic above the shower, or does it have to be further away to be considered out of a wet area?

the remote fan I am thinking of using:

Fantech PB110 100 CFM Ceiling Mounted Bathroom Exhaust Fan 4in. Duct PB110 - The Home Depot

Update your bathroom by adding this Fantech PB Ceiling Mounted Bathroom Exhaust Fan Duct.

www.homedepot.com

 

[BrandonV]

You're going to want to individually vent or massively upsize the existing duct.

There is almost a 100% chance the exhaust ductwork to the outside is undersized for whatever fan you have now. Another fan isn't going to help without removing the restriction.

 

[Paulski]

You're going to want to individually vent or massively upsize the existing duct.

There is almost a 100% chance the exhaust ductwork to the outside is undersized for whatever fan you have now. Another fan isn't going to help without removing the restriction.

The current vent fan is ridged semi flex 4" duct, running straight to the outside wall about 3-4' away. It is close to the wall, so adding in a wye splinter might be tight.

 

[BrandonV]

The current vent fan is ridged semi flex 4" duct, running straight to the outside wall about 3-4' away. It is close to the wall, so adding in a wye splinter might be tight.

What is the CFM rating on the existing fan?

For 4" flex, the maximum CFM per code is 80 CFM for a 4' maximum distance.

Mind you the code also says, "Duct length shall not be limited where the duct system complies with the manufacturer’s design criteria or where the flow rate of the installed ventilating equipment is verified by the installer or approved third party using a flow hood, flow grid or other airflow measuring device."

I prefer to use the conservative code values over the manufacturer's excuse to run crazy long flex duct but realistically two fans over a 4" flex duct is going to struggle.

 

[Paulski]

What is the CFM rating on the existing fan?

For 4" flex, the maximum CFM per code is 80 CFM for a 4' maximum distance.

Mind you the code also says, "Duct length shall not be limited where the duct system complies with the manufacturer’s design criteria or where the flow rate of the installed ventilating equipment is verified by the installer or approved third party using a flow hood, flow grid or other airflow measuring device."

I prefer to use the conservative code values over the manufacturer's excuse to run crazy long flex duct but realistically two fans over a 4" flex duct is going to struggle.

The current one is only rated for 70cfm. The new remote mount fantech is 100cfm so I will need to run separate ducts, thank you.

 

[hobie18]

When I read the title

 

[fitter30]

Fan timer switch will let the fan to run longer and don't have to worry about shutting it off. Most bathrooms need 20-30 minutes of run time after a shower.
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[PoorUB]

Just add the timer and run the current exhaust fan longer. A lot less hassle and probably cheaper in the long run too. Also, leave your shower door or curtain open to promote airflow. 70 CFM exhaust should be more than enough.

Also, if you ventilate fast you have a good chance of not removing all the moisture. Water on the shower walls needs to evaporate before you can exhaust it. If you ventilate for say 10-15 minutes there is a good chance there will be moisture left behind, where a longer fan run time will allow the moisture to evaporate and get vented out.

I have a push button timer in both bathrooms and run the fan for another 30-45 minutes after a shower and no mold problems.

 

[CTyankee]

Fan timer switch will let the fan to run longer and don't have to worry about shutting it off. Most bathrooms need 20-30 minutes of run time after a shower.

Also a necessity due to the possibility of failure and fire.

 

[duneslider]

Also, how sealed up is the bathroom once you are done? If the door is shut can 70cfm of air make it into the bathroom? Leaving the door open can help if you aren't already doing that. Also, like someone else mentioned, leave the shower door/curtain open until dry.

 

[hobie18]

There are moisture sensing fans now. Helps.

 

[Shiftless]

The current one is only rated for 70cfm.

If your fan is old, it probably doesn’t move even that. Start with installing a timer switch so it will run for a while after you finish your shower. I installed one of those to let the fan run an hour after showering. I also dry off the shower walls with a separate towel before getting dressed. 100 CFM Panasonic fan, 4 inch rigid duct. No mold.

 

[kaymccampbell]

If your fan is old, it probably doesn’t move even that. Start with installing a timer switch so it will run for a while after you finish your shower. I installed one of those to let the fan run an hour after showering. I also dry off the shower walls with a separate towel before getting dressed. 100 CFM Panasonic fan, 4 inch rigid duct. No mold.

Absolutely buy a Panasonic fan. The cost will shock you, but the performance is amazing. And they're really quiet for the air they move. You won't need a second fan.

 

[CTyankee]

Also, how sealed up is the bathroom once you are done? If the door is shut can 70cfm of air make it into the bathroom? Leaving the door open can help if you aren't already doing that. Also, like someone else mentioned, leave the shower door/curtain open until dry.

Good point. High(er) flow exhaust fans today aren't your grandpa's fans. After a few fogging issues despite having longer run times, we learned to leave a good 1/2" gap under bathroom doors as to provide enough flow into the room.

 

[Steve_P]

I have a Panasonic fan in two bathrooms- they're definitely nice, super quiet. As said, a huge improvement is to leave the bathroom door at least cracked while showering. If that's not an option, make sure there's a half inch gap at the bottom.

 

[larry4406]

I have a Panasonic fan in two bathrooms- they're definitely nice, super quiet. As said, a huge improvement is to leave the bathroom door at least cracked while showering. If that's not an option, make sure there's a half inch gap at the bottom.

I have installed two of the Panasonic Whisper Choice 80/110 CFM bath fans (2 different bathrooms) and have been quite impressed with how quite they are and how powerful they are. I set both to 110CFM.

 

[onewheat]

Another thing to help remove moisture is squeegee-ing down your entire shower after using it. You will get a lot more moisture down the drain that doesn't need to evaporate and be vented out.