Unused B-vent For Bathroom Fans? - Kitchen & Bath Remodeling - DIY Chatroom Home Improvement Forum
Advertisement


Go Back   DIY Chatroom Home Improvement Forum > Home Improvement > Remodeling > Kitchen & Bath Remodeling

CLICK HERE AND JOIN OUR COMMUNITY TODAY...IT'S FREE!

Reply
 
Thread Tools
Display Modes
Old 08-12-2019, 09:23 AM   #1
Member
 
Join Date: Mar 2018
Posts: 113
Rewards Points: 226
Default

Unused B-vent for bathroom fans?


I know it is a bit of a stretch... but after converting to high efficiency furnace/water heater, I have an unused B-vent, and two bathroom fans that are hack vented into the attic space. Wondering if I can kill two birds with one stone here. I am guessing it may be more trouble than it is worth vs paying someone (or DIY) to put new holes through the roof.
Attached Thumbnails
Unused B-vent for bathroom fans?-img_3675.jpeg  
gslenk is offline   Reply With Quote
Sponsored Links
Advertisement
 
Old 08-12-2019, 09:47 AM   #2
Member
 
Join Date: Dec 2017
Posts: 3,691
Rewards Points: 1,406
Default

Re: Unused B-vent for bathroom fans?


Probably could, using something like this wye while adapting it to the EF's 3 or 4 inch duct sizes needed. Just be SURE to remove what is left of the 6 inch duct that goes through the ceiling and seal it back properly. Fireproofing/heat/cool loss issue.. if not done. And it may also need watching just in case the wye sweats in the attic, from the cold bathroom exhaust air hitting the hot attic duct. Reflectix insulation on the duct works well for this issue.

https://www.homedepot.com/p/Speedi-P...-866/202907307
__________________
...

Last edited by Gregsoldtruck79; 08-12-2019 at 09:53 AM.
Gregsoldtruck79 is offline   Reply With Quote
Sponsored Links
Advertisement
 
Old 08-12-2019, 11:50 AM   #3
Member
 
Join Date: Mar 2018
Posts: 113
Rewards Points: 226
Default

Re: Unused B-vent for bathroom fans?


My first concern was that the design/materials of the B-vent duct and roof topper would be able to handle the CFM and humidity of the two bathroom fans.

The fans are 10" straight through (https://www.homedepot.com/p/Broan-35...-504/100662374)

The rest of my concerns are (hopefully they are non-issues):

1) Installation instructions state to use 10" ducting, or 8". Would eventually, or even immediately reducing to 6" be ok?

2) Don't know if installing the damper vertically will fit, at least one might have to be horizontal

3) I suppose the ducting should be sloped back to the fan so condensation does not collect anywhere. Maybe add some kind of drain system? Or is not a problem once the pipes are insulated?

4) Each fan will need two 90 degree elbows, one is 6ft over horizontally, the other is 2ft over. Is this going to hinder airflow.

5) I read somewhere that if you wye two bathroom fans, there needs to be a third fan past the wye to avoid crossover/backdrafts. I thought that is what dampers are for...

I would be willing to change to a different fan system if it is more compatible than what I currently have. These are some obnoxiously loud fans anyway. Closing up the holes/insulation/drywall is exactly what I intend to do regardless. I just recovered a lot of closet space by removing the chase.

Last edited by gslenk; 08-12-2019 at 12:00 PM.
gslenk is offline   Reply With Quote
Sponsored Links
Advertisement
 
Old 08-12-2019, 11:59 AM   #4
retired framer
 
Join Date: Jun 2017
Location: Fraser Valley BC Canada
Posts: 25,250
Rewards Points: 18,390
Default

Re: Unused B-vent for bathroom fans?


I think the general rule is one each so I think you are just asking for trouble
__________________
Do not use flat bottom gables with scissor trusses.
Nealtw is online now   Reply With Quote
Old 08-12-2019, 12:34 PM   #5
Member
 
Join Date: Dec 2017
Posts: 3,691
Rewards Points: 1,406
Default

Re: Unused B-vent for bathroom fans?


Old Master of All say, …" Pertinent and accurate information given in an OP, helps keep those that reply first to the OP.... from giving incorrect advice."


So ignore my first reply. Two ten inch ducted exhaust fans should not be vented in to a 6 in. round duct.
__________________
...
Gregsoldtruck79 is offline   Reply With Quote
Old 08-12-2019, 03:27 PM   #6
Member
 
Join Date: Mar 2018
Posts: 113
Rewards Points: 226
Default

Re: Unused B-vent for bathroom fans?


Ok so definitely a no go on doing both, or any of the existing fans. Say I wanted to vent the closer one, and changed models, to a 6" outlet. Depending on orientation of the replacement, I am looking at 2 to 3 ft offset horizontally and about 2ft up.

Could something be made to work, correctly, or should I just completely abandon the idea in favor of shooting straight up out of the roof to a vent designed for the intended purpose?
gslenk is offline   Reply With Quote
Old 08-12-2019, 03:35 PM   #7
retired framer
 
Join Date: Jun 2017
Location: Fraser Valley BC Canada
Posts: 25,250
Rewards Points: 18,390
Default

Re: Unused B-vent for bathroom fans?


Quote:
Originally Posted by gslenk View Post
Ok so definitely a no go on doing both, or any of the existing fans. Say I wanted to vent the closer one, and changed models, to a 6" outlet. Depending on orientation of the replacement, I am looking at 2 to 3 ft offset horizontally and about 2ft up.

Could something be made to work, correctly, or should I just completely abandon the idea in favor of shooting straight up out of the roof to a vent designed for the intended purpose?
I am sure you could use the same hole for one but if you remove that pipe the hole in the ceiling needs to be closed properly to assure no leaks into the attic.
__________________
Do not use flat bottom gables with scissor trusses.
Nealtw is online now   Reply With Quote
Old 08-12-2019, 06:19 PM   #8
Member
 
Join Date: Mar 2018
Posts: 113
Rewards Points: 226
Default

Re: Unused B-vent for bathroom fans?


Closing off the ceiling/attic hole is the current project. Unless you were talking about the actual b-vent and top on the roof. I capped it when the furnace/WH were replaced and monitored it for water/etc., bone dry and no animals/bugs.
gslenk is offline   Reply With Quote
Old 08-12-2019, 06:21 PM   #9
retired framer
 
Join Date: Jun 2017
Location: Fraser Valley BC Canada
Posts: 25,250
Rewards Points: 18,390
Default

Re: Unused B-vent for bathroom fans?


Quote:
Originally Posted by gslenk View Post
Closing off the ceiling/attic hole is the current project. Unless you were talking about the actual b-vent and top on the roof. I capped it when the furnace/WH were replaced and monitored it for water/etc., bone dry and no animals/bugs.
That is what I meant, use the same hole for the boot vent and close up and seal the ceiling. I fixed up a friends bathroom in a suite where there made a special boot outside for three vents side by side range bath and dryer. When the dryer was running, it would suck air back into the bathroom and kitchen unless the door was open.
__________________
Do not use flat bottom gables with scissor trusses.

Last edited by Nealtw; 08-12-2019 at 06:26 PM.
Nealtw is online now   Reply With Quote
Old 08-12-2019, 07:31 PM   #10
Member
 
Join Date: Mar 2018
Posts: 113
Rewards Points: 226
Default

Re: Unused B-vent for bathroom fans?


Any benefit in closing the b-vent hole, and making two new holes directly above each fan? Or is that wasted effort/money?
gslenk is offline   Reply With Quote
Old 08-12-2019, 07:35 PM   #11
retired framer
 
Join Date: Jun 2017
Location: Fraser Valley BC Canada
Posts: 25,250
Rewards Points: 18,390
Default

Re: Unused B-vent for bathroom fans?


Quote:
Originally Posted by gslenk View Post
Any benefit in closing the b-vent hole, and making two new holes directly above each fan? Or is that wasted effort/money?
Maybe length of duct or how it would look from outside, but if those work cutting a new hole and closing one doesn't make sense. Closing one would require new matching shingles??
__________________
Do not use flat bottom gables with scissor trusses.
Nealtw is online now   Reply With Quote
Sponsored Links
Advertisement
 
Reply


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off





Top of Page | View New Posts