Bathroom Fan Replacement Question

[JWILLIE1977]

The 50cfm Broan bathroom vent fan in my 12x12 bathroom just let the smoke out. Tried removal, full cleaning, and reinstall. . . But she's done.

Looking at replacements. . It seems the 50cfm fan is very undersized for a 12x12 space.

New 100 or 150 CFM fans come with larger, 4" or 6" ducting. Will I be creating issues if I adapt the larger fan duct to the existing, smaller vent ducting? Or do I need to replace all the ducting from the new fan out the roof?

 

[PCustoms]

What size is the old duct?

You're not going to cause "problems", but it could be noisy and definitely won't work at full capacity. Small ducts can only flow so much air.

Does this bath have a tub/shower?

Have you looked at replacing just the guys to the existing fan?

 

[Fav Onefour]

Do you currently have one of the standard Broan units? Quite a few use the same dimension spec box. It might be worth trying an upgrade kit.
I like to keep things easy with bath fans. With simple guts, replacement is a ten minute job. In most cases a new motor is already a big improvement. (They usually make a lot of noise for quite some time before they **** out.) I had motor **** out on a fancy ****** last year and the replacement was nearly the price of a new fan. That one I tore out and replaced with a more common version. I like having fans that work without all the noise. Stick to basic models with good sone numbers and use a timer to move enough air.

 

[Shiftless]

For a big bathroom with a shower, I recommend at least 100 CFM or better yet a 150. Plus, wire it up with a timer switch. That way, you can just turn it on like I do for an hour and then it will continue to pull out moist air after you leave the room. This modification along with squeegeeing or toweling off the wet shower walls has greatly reduced the mold problem we used to have.

I‘m a big fan of Panasonic brand. I put those in both of our bathrooms. Don’t skip the timer switches.

If your 3 inch exhaust is rigid steel (not crappy corrugated), without a lot of ells and not too long, I think you’d be OK with adapting the new fan to the old vent tubing. When I remodeled, the inspector insisted on 4 inch exhaust tubing to match the fan manufacturer’s requirements even though it was a straight shot of 10 feet with 2 ells.

 

[Norcal]

Even better then a timer is a humidistat, when the main bath was remodeled I installed one & quite pleased with it.

 

[JWILLIE1977]

Sorry for skimping on the details.

Yes it is a full bathroom with a stand-up shower. The existing fan is 3 in. Exiting the housing.

I would really like to stay away from replacing the existing 50 CFM fan guts and upgrade to a larger unit. We have excessive condensation on the walls which leads me to believe that the 50 CFM is just too small for this size room

I am right now in process of getting into the Attic to determine the existing duct size that goes through the roof.. from what I can see from the bathroom and the outside of the house there should be very view fence or turns in the ducting that is in the Attic.
But I'll know more by early afternoon.

Currently I am leaning towards a 100 CFM Panasonic with four inch ducting. .. or if I can install without a major hassle. . The bigger 150 CFM Panasonic with 6 in ducting

 

[kbuhagiar]

If you are going through the trouble to upgrade to a larger size, seriously consider the Panasonic unit.
It's definitely worth the cost and effort.
It's so quiet that quite frequently I have to look at the integrated light to see if it's on or off.

 

[Fav Onefour]

Even better then a timer is a humidistat, when the main bath was remodeled I installed one & quite pleased with it.

I have four with humidistat controls. They are nice. I will caution that the buggers will run a lot if you don't pre -start before the shower. It's surprising how much moisture a bath will kick out.

I dial mine in around 45-50% and high ambient will also kick them on. Sometimes the setup is a good reminder that I better check the humidity in the home.
@JWILLIE1977 , Do you know what humidity level you are at in the home? I do like your approach to doing it right and going bigger if you are going to do the work. I also agree that a tired 50 cfm isn't up to the task. I will caution that a big fan will still only "reduce" humidity in the bath. The biggest fan in the world will not lower it below the home's ambient.

I have two Panasonic units that are super quiet. They do a slow ramp to speed as well. I have looked for the indicator light at times after switching them on just to make sure they were running. They are pretty sweet fans. I have not gone through replacement yet, so I'll reserve my final judgement.
BTW, if you go to a humidistat setup, use the K.I.S.S. concept and do it in a wall switch. Adjustments and tuning are easier. I leave the little cap partially loose until I get them dialed. The other benefit is that repairs and or replacement are cheaper.

 

[ItsNemo]

I've got three of these Panasonics in the house:

Amazon.ca

They're dead silent, I use them on the high 110cfm setting, and are easy to install. They will adjust for static pressure to maintain flow at the expensive of noise, not sure I'd want to have a 3" duct with them though on high.

 

[larry4406]

I've got three of these Panasonics in the house:

Amazon.ca

They're dead silent, I use them on the high 110cfm setting, and are easy to install. They will adjust for static pressure to maintain flow at the expensive of noise, not sure I'd want to have a 3" duct with them though on high.

I put one of these Panasonics in the new basement bath based on recommendation from day job hvac foreman.

Man is it quiet! I also flipped the switch to max.

Mine is on a long run I’m guessing 50’. I used 4x5 adapter at fan, ran 5” metal duct the whole way to end, then 4x5 reducer to mate with the wall cap. Outside it pegs the flapper to max open and flows a lot.

I will install one of these in the just started hall bath renovation, and then master bath renovation after that.

 

[PCustoms]

I don't get the fascination with dead quiet bath fans... sometimes you need a little noise.


My house never had one. When I renovated I put an exhaust fan mounted between two trusses in the attic. About 6' of 4" duct down to the ceiling, then 20' of duct straight to the vent in the roof. Moves tons of air and gives enough wind noise to offer some privacy.

 

[Snapped-off]

I just bought a new motor for the Broan in our 2nd bathroom. I'd wager it's probably 20-30 years old. I think it's 80cfm.

Check that out before replacing the whole thing, unless you want to upgrade.

 

[ItsNemo]

I don't get the fascination with dead quiet bath fans... sometimes you need a little noise.


My house never had one. When I renovated I put an exhaust fan mounted between two trusses in the attic. About 6' of 4" duct down to the ceiling, then 20' of duct straight to the vent in the roof. Moves tons of air and gives enough wind noise to offer some privacy.

It's nice not having the drone of a fan when you want peace and quiet getting ready in the morning or something...our powder room on the main floor has a noisier fan if guests want a bit of privacy.

 

[JWILLIE1977]

Thanks for all the responses!

Got up in the attic. And this is what I found. .



3" galvanized duct that dumps out into the soffit.

The moist air moved out by existing fan doesn't daylight past the soffit. The soffit is vented approximately every
Is this an issue?

I feel like the moist air can get blown back into the attic if there's a breeze from the outside against the soffit.



The end of the ducting appears to be directly above the vented portion of the soffit above the top left of the window.


If all this is proper procedure, I feel like the best route is to pick up the Panasonic 150cfm fan, replace the 3" duct with the appropriate 6" duct. . And bam. . Bob's ur uncle. . . Right??

 

[PCustoms]

Thanks for all the responses!

Got up in the attic. And this is what I found. .



3" galvanized duct that dumps out into the soffit.

The moist air moved out by existing fan doesn't daylight past the soffit. The soffit is vented approximately every
Is this an issue?

I feel like the moist air can get blown back into the attic if there's a breeze from the outside against the soffit.



The end of the ducting appears to be directly above the vented portion of the soffit above the top left of the window.


If all this is proper procedure, I feel like the best route is to pick up the Panasonic 150cfm fan, replace the 3" duct with the appropriate 6" duct. . And bam. . Bob's ur uncle. . . Right??

Yeah, that's not venting correctly. See the staining on the underside of the OSB? Moisture is being sucked right back into attic, if it ever vented to begin with.

I would add a roof vent.

At minimum you could do an actual vent in the soffit, and replace that vented section with solid. But really this isn't the right way to go and is compromising your already limited soffit vents.

 

[The Cobbler]

that's not a correct install, just look at the mould on the roof sheathing above from moisture .
do it right, vent it to the outside with appropriate sized pipe & a soffit cap

 

[PCustoms]

Would going left, on top of the joist, and out the gable be easier?

 

[JWILLIE1977]

Thanks PC and Cobbler.


Awesome! Just what I need! More work!

Looks a bigger project, as the adjacent kids bathroom is probably vented exactly the same way!

So looks like the new plan is. . Find decently color matched vent fixtures to get the moist air out of the soffit.. . And get up on the ladder!

How does this stuff pass the building inspector? House was built on 2004. We moved in June of '22.

Would going left, on top of the joist, and out the gable be easier?

Not harder No easier. . . I think I would prefer the vent fitting in the soffit. . So I'm leaning that way now.

We are still a few years away from need a new roof, so I think the soffit vent is the right way to go right now.

Thanks for all the assistance guys!!

 

[larry4406]

@

Thanks PC and Cobbler.


Awesome! Just what I need! More work!

Looks a bigger project, as the adjacent kids bathroom is probably vented exactly the same way!

So looks like the new plan is. . Find decently color matched vent fixtures to get the moist air out of the soffit.. . And get up on the ladder!

How does this stuff pass the building inspector? House was built on 2004. We moved in June of '22.



Not harder No easier. . . I think I would prefer the vent fitting in the soffit. . So I'm leaning that way now.

We are still a few years away from need a new roof, so I think the soffit vent is the right way to go right now.

Thanks for all the assistance guys!!

Our house 1987 build the fart fans dumped into the attic! Yes inspected.

With a hipped roof my only choice was to add roof jacks and vent there.

 

[PCustoms]

Thanks PC and Cobbler.


Awesome! Just what I need! More work!

Looks a bigger project, as the adjacent kids bathroom is probably vented exactly the same way!

So looks like the new plan is. . Find decently color matched vent fixtures to get the moist air out of the soffit.. . And get up on the ladder!

How does this stuff pass the building inspector? House was built on 2004. We moved in June of '22.



Not harder No easier. . . I think I would prefer the vent fitting in the soffit. . So I'm leaning that way now.

We are still a few years away from need a new roof, so I think the soffit vent is the right way to go right now.

Thanks for all the assistance guys!!

I'm about to lose cell reception for the next several hours so I can't walk you through this right now, but I would strongly consider a wall vent on the Gable end over trying to vent through the soffit much more effective and can actually be a permanent event solution.

Cutting into an existing roof isn't for the faint-hearted, and can **** with snow loads in certain situations

 

[JWILLIE1977]

Thanks PC.

We have time on this. Rome wasnt built in a day!

I'll wait to hear what you have to say.


Some more food for thought. . .

Because the kids bathroom is most likely vented the same way. . . I will be doing both fans and duct.
Both fans are at the same offset from the rear wall. . .
If the gable vent option is better, is there code preventing me from venting both fans with the same duct?

 

[PCustoms]

Thanks PC.

We have time on this. Rome wasnt built in a day!

I'll wait to hear what you have to say.


Some more food for thought. . .

Because the kids bathroom is most likely vented the same way. . . I will be doing both fans and duct.
Both fans are at the same offset from the rear wall. . .
If the gable vent option is better, is there code preventing me from venting both fans with the same duct?

Well plans didn't exactly pan out, so I've got some time.

Basically the soffit vent, while an improvement over what you have, still isn't great. I also suspect that your roof is under vented to start, so you probably just want to get away from there.

Roof penetrations can be a hassle. The Gable is best option IMHO, as you get a correct vent without the risk of a roof penetration.

There's a bunch of good articles out there. Some pics I stole:





I'd get this:

Ply Gem 6.625 in. x 6.625 in. White D4 and D5 Surface Mounting Block BLK040H04H - The Home Depot

The Cellwood D4 and D5 Surface Mounting Block is used to mount accessories after Double 4 in. or Double 5 in. lap siding has been installed. It helps present a level transition from siding to mounted fixtures. Cellwood Mounting Blocks are built to withstand the toughest weather and retain their...

www.homedepot.com

And this:

Everbilt 4 in. Heavy Duty Exhaust/Intake Hood in White VTH0004 - The Home Depot

This Imperial Premium 4 in. Wall Exhaust/Intake Hood is an energy-efficient venting solution ideal for use with bath fans and range hoods. It features an innovative airtight damper door that helps prevent

www.homedepot.com

Drill the siding block 4"+ on center to clear the pipe. Then determine the general area you want to come out, and drill the same size hole, using the block as the guide. Install the block using OSI quad max adhesive on the back (skinny) surface, plus a bead along the top edge. Once that cures its effectively glued to the sliding. Apply some adhesive to the vent as well, and use a couple screws to secure the vent/mount block to the house.

From there it's a matter of connecting and insulating the pipe in the attic.

Note: you might find better options on the block and vent, that's just what I pulled up quick.

Regarding 2 fans into one vent, I'm not sure if there is a code that prohibits it, but you'd have to add damper(s) to make sure on fan doesn't blow into the other. One way could be a remote mounted fan with a wye on the inlet to pull from each bathroom.

 

[Fav Onefour]

@JWILLIE1977 , I'm impressed with the investigating that you have done already. I'm guessing you are not afraid to do the work it takes to run new venting. I'd also say that you are on the right path with your thinking on doing both bathrooms. Might as well while you are digging around up there.


This picture and description is very good.
I'll admit that I have not added cape dampers. It seems like a good idea. I have a north wall outlet that gets noticeable colder when the wind is whipping.
Slope on the hard line is ignored on a lot of installs I've dealt seen. I'd say it's crucial along with sealing the joints. Condensation is more than you might imagine. Slope is a challenge with low height outlets on the fans. One trick is to use a short section of good flex right out of the fan up to the straight pipe. That also helps with retrofit installation.

BTW, do your fan box fasteners from below and inside the new fan enclosure. I like to have a good two sided L box frame to the trusses. It makes a nice solid mount and if you need to replace the fan enclosure down the road it will be easier.

I'm not a fan of putting both into a single outlet. I'm sure it will better than the existing setup but you're already doing half the work to get it right. Might as well finish the job.

 

[Ak Jim]

Since you’re up there definitely vent it out the gable end.

 

[nicks78camaro]

Depends how the attic is vented. If it has proper soffit and ridge vents, then sure vent it out the nearest gable end.

If relying on the gables to vent the attic, go out the wall or the roof deck.

 

[southalabama]

I learned this lesson the hard way on an inaccessible vent fan.

There are two types. New install and replacements that can all be done from inside the house.

 

[ambenz]

My unit died too so I bought one of these...

VENTS-US 4" White Corded In-Line Duct Fan with Silencer Model Number: TTSILENT100 ​

I used the old fans ceiling box to connect electrical plug and duct work, then I placed the fan high in the attic so it is super quiet but sucking at 146 cfm. When we re-roofed, I added a roof vent. Now it super easy to get to....and no fan noise!

 

[Norcal]

I have four with humidistat controls. They are nice. I will caution that the buggers will run a lot if you don't pre -start before the shower. It's surprising how much moisture a bath will kick out.

I dial mine in around 45-50% and high ambient will also kick them on. Sometimes the setup is a good reminder that I better check the humidity in the home.
@JWILLIE1977 , Do you know what humidity level you are at in the home? I do like your approach to doing it right and going bigger if you are going to do the work. I also agree that a tired 50 cfm isn't up to the task. I will caution that a big fan will still only "reduce" humidity in the bath. The biggest fan in the world will not lower it below the home's ambient.

I have two Panasonic units that are super quiet. They do a slow ramp to speed as well. I have looked for the indicator light at times after switching them on just to make sure they were running. They are pretty sweet fans. I have not gone through replacement yet, so I'll reserve my final judgement.
BTW, if you go to a humidistat setup, use the K.I.S.S. concept and do it in a wall switch. Adjustments and tuning are easier. I leave the little cap partiallgny loose until I get them dialed. The other benefit is that repairs and or replacement are cheaper.

I cool with a evap cooler & the bathroom door has to be closed or the fan will come on, that is the downside of the humidistat, also was going to install a Panasonic fan but would not fit in the space I had for it, so it went back on the shelf & spend $120 for a Broan unit which is very quiet, the Panasonic was only about $65 NIB at the Restore, I'll use it to replace a cheap fart fan in another bathroom.

 

[PopcornSutton]

One of our bathrooms didn't have a fan since it had a window, which was OK back in the 80's when built. I cut in a ceiling register and installed an inline fan similar to what ambenz shows. Back draft damper at the register and the fan I mounted to a truss member with flex duct connecting. The fan is about 3 feet above the bottom truss cords where the insulation is and the fan outlets into the attic space. The attic is vented with gable end louvers, one which has an attic fan. I guess that install isn't proper per the comments here, but the fan runs maybe 10 minutes a day when I shower. I could hard duct it to a gable end if I had to.

 

[MoonRise]

Running two vent fans into one exhaust line and vent exit is usually NOT allowed, because as mentioned you can easily get a backflow condition of venting one fan/duct INTO the other.

And an exhaust vent into the attic itself is NOT allowed. A vent MUST vent to the outside.

As mentioned, your existing 'vent' isn't venting properly. As seen by the black mold/mildew in the soffit area where all the moisture is either not even getting out of the house in the first place or is just getting sucking right back into the perforated soffit and back into the attic.

Gable vent is the way to go. One vent line and one vent cap for each bathroom vent. Each duct line taped/sealed AND insulated. Proper pitch for the duct line. No roof penetration or possible ice damming in the winter or having snow block the roof jack (vent cap) or blow back into the vertical vent duct and then drip into the bathroom duct grills.

Or you might go with one in-line fan pulling from both bathrooms and exhausting through one gable-end vent cap.

Inline Exhaust Fans: How to Use Them to Vent Multiple Bathrooms

An inline exhaust fan in your attic can vent multiple bathrooms. Here's everything to know, including how to install.

www.familyhandyman.com

12x12 bathroom (one bathroom) pretty much calls for a 150+ cfm exhaust fan just for that one bathroom. In general, you need/want 1 cfm of fan for each 1 ft2 of bathroom. So yeah, that original 50 cfm fan was waaaay undersized.

So with two bathrooms (assuming roughly the same size/area), you'd be looking at a 300+ cfm fan if you did the single in-line fan pulling from one vent grill in each bathroom. Might be better to run individual exhaust fans for each bathroom, with their own ducts and exhaust caps.

 

[JWILLIE1977]

All,

Thanks for the responses!!
Learning as I go.

As PC suggested, I am going to research the gable end venting, rather than the soffit.

I think I am leaning towards both fans having their own pitched pvc ducting.

This is a decent sized project for me, in the summer, when my free time is non existent, so I will be pausing to gather more info, obtain the parts, and will return with progress updates as they become available.

Thanks again for all the advise!!

 

[Norcal]

All,

Thanks for the responses!!
Learning as I go.

As PC suggested, I am going to research the gable end venting, rather than the soffit.

I think I am leaning towards both fans having their own pitched pvc ducting.

This is a decent sized project for me, in the summer, when my free time is non existent, so I will be pausing to gather more info, obtain the parts, and will return with progress updates as they become available.

Thanks again for all the advise!!

Attic work is best done in cooler weather, if possible.

 

[75gmck25]

For gable venting, make sure you angle the horizontal vent pipe slightly downward toward the gable end. Moisture will condense in that pipe and you want it to run down hill and out of the house.

 

[gregs]

What do you do for the condensate on a vertical outlet that is close to the fan? Lets say you have the fan and about 3 feet away is a roof cap for the vent to go to.

 

[NUTTSGT]

I'll throw this out there. You got lucky. Over my career, I've seen about a half dozen attic fires start due to bathroom exhaust fans burning up.

 

[PCustoms]

I'll throw this out there. You got lucky. Over my career, I've seen about a half dozen attic fires start due to bathroom exhaust fans burning up.

Any more details?

Insulation issues? Fluke event?

This is concerning

 

[NUTTSGT]

Any more details?

Insulation issues? Fluke event?

This is concerning

That great blown in cellulose insulation will sit there and smolder. It hold the heat in and will completely burn out a section of the rafter/truss.

 

[welder4956]

Thanks PC and Cobbler.


Awesome! Just what I need! More work!

Looks a bigger project, as the adjacent kids bathroom is probably vented exactly the same way!

So looks like the new plan is. . Find decently color matched vent fixtures to get the moist air out of the soffit.. . And get up on the ladder!

How does this stuff pass the building inspector? House was built on 2004. We moved in June of '22.



Not harder No easier. . . I think I would prefer the vent fitting in the soffit. . So I'm leaning that way now.

We are still a few years away from need a new roof, so I think the soffit vent is the right way to go right now.

Thanks for all the assistance guys!!

I'm planning to add vents in our upstairs bathrooms and ordered a couple of these: https://soffitvent.com/shop/soffit-vent-for-bathroom-fan





Might work for your application as well.

 

[PCustoms]

I'm planning to add vents in our upstairs bathrooms and ordered a couple of these: https://soffitvent.com/shop/soffit-vent-for-bathroom-fan





Might work for your application as well.

I had something very similar as a temp solution in my massively over vented 8' deep porch/soffit

1. The damn thing would ice up in the winter
2. The issue with a soffit vent is the soffit should be drawing air up and into the attic at all times. The exhaust right there curls around and gets sucked right in

This might address #2 by pushing it to the outer edge, but looks gimmicky to me.

 

[larry4406]

For gable venting, make sure you angle the horizontal vent pipe slightly downward toward the gable end. Moisture will condense in that pipe and you want it to run down hill and out of the house.

And if using metal duct put seams at top and make sure male/female ends engage properly.

Male points towards flow direction.

Any condensate will then run out.