Bathroom fan exhaust vent

[CMV]

Replaced my builder-grade, plain plastic loud bathroom fan with a lighted one a few yrs back. Well, it's getting rusty and looks like a turd so is getting replaced again soon. When I put 1st one in, I noticed it just vents between the ceiling and 2nd story floor. There is a vent on exterior wall, but nothing ducts this fan nor the other one in the tiny little commode closet part of the bathroom to that vent.

Should these fans just discharge into the empty space between ceiling & floor or should they be ducted to that vent to exhaust directly outside? It's the way house was built so I just left it that way, but have wondered about it ever since. Doesn't seem like the fan by the shower should be sending that moist air between the floors. The vent on exterior wall is probably straight line distance 8-9' from either fan.

While installing fan the 1st time, I noticed I could see a lot of daylight from the exterior vent cover, so I guess there is some breathing going on between the floors. I didn't see any signs of moisture, mildew, water damage, etc - looked normal. But house was only 5 y/o at the time. Anyway, just wondering if that's normal/acceptable that bathroom exhaust fan just vents into open space between the floors or if it should have some sort of duct directing that moist air directly outside?

 

[LouNY]

I do believe it should have been ducted.

 

[teejk]

Sounds like somebody short cut the venting (maybe they forgot to do it before the sheet rock was up). Also sounds like they made it appear to be vented outside to get past inspection. That much moisture is not a good thing (mold, etc.).

 

[RNeumann]

Yes it should be vented to the outside. It’s worse to vent that into the floor cavity. Seeing daylight isn’t good either. Most of that stuff can be sealed from the outside.......it’s not the best but it it’s better than nothing.

 

[EddieWalker]

Yes, it should be vented. Are they always vented in every house? no I used to be very paranoid about this, but over the last couple of decades, it's so common that I no longer even pay attention to it in homes that I'm working on. I have never seen any moisture issues or mold from a non ducted vent. I personally install the ducting because it's simple and that's how it's supposed to be done, but I wouldn't lose any sleep over it if there wasn't a duct, or if it just goes up into an attic and not outside.

Do you see any sign of moisture or mold?

 

[3Ts]

It's supposed to be vented to the outside. There are building codes covering this along with what size of duct is supposed to be used based on the fan's cfm and length of duct.

 

[KennyG]

Not surprising. I found one not vented to the outside when I remodeled my house. Took a bit of work to snake a vent through and fix it. As an aside, when we remodeled we took the contractors advice and got Panasonic vent fans. They are almost silent and well worth it. I cringe every time I go into an expensive house and hear the economy grade fans.

 

[kcflhrc]

You will find the majority not vented to the outside. I have yet to see an issue with it.

 

[jk96]

+1 on Panasonic bath fans. We had a lightning strike on our home that took out all of the bath fans in the home. If you ever have to replace them Panasonic retrofit fans are really slick the way they install. Makes it really simple to replace the existing fan.

 

[jk96]

Also if you want to help with backdrafts from the vent to outside install a backdraft damper inline of your ducting. These work much better than the ones you see as part of the bath fans.

RSK4 - Fantech RSK4 - RSK Series 4" Duct Backdraft Damper

 

[HillStreet]

You will find the majority not vented to the outside. I have yet to see an issue with it.

I don稚 know the weather in KC but up here we not only vent to the outside, but we insulate the duct too. I don稚 know how the wet, warm exhaust could dissipate into the attic, or between floors without leaving condensation. Warmer air will condense when it hits cooler air.

 

[jk96]

I don稚 know the weather in KC but up here we not only vent to the outside, but we insulate the duct too. I don稚 know how the wet, warm exhaust could dissipate into the attic, or between floors without leaving condensation. Warmer air will condense when it hits cooler air.

I'm not too far from the KC area and yes all fans should be vented to the outside of the home. As Eddie mentioned you will find a lot of homes not built recently that have venting into the attic. While not a good practice it is a lot more forgiving then the ops situation where his is vented between the floor joists. Since he has an outside vent that's not connected I think the earlier post had it correct in that the sheetrockers likely got ahead of the HVAC guys.

 

[Tomtint]

Always vent to the outside of the house. The fans are supposed to suck smell...and moisture from the room ( steam from the shower ) and simply dumping it into a space in the attic or betweenfloors..is a recipe for mold.

 

[Tractor Seabee]

If you can see daylight through the cavity should be easy to snake that aluminum flex pipe in there. Not sure how long you can get it but it's not hard to couple lengths together. connect it to the fan first. I would use an electricians pull snake to keep it moving to the exterior. As all have said, it is necessary to do. It is probably not if you will have problems but when. On a cold day here with the shower going there is a huge plume of water vapor coming from my vents. But I like hot showers and have large very quite fans. Quietest ones Lowe's sells.

Ron

 

[4570Man]

They’re supposed to be vented outside by code but I don’t think venting to the attic hurts anything. Venting between the floors seems like a bad idea.

 

[kcflhrc]

They’re supposed to be vented outside by code but I don’t think venting to the attic hurts anything. Venting between the floors seems like a bad idea.

That code would depend on where you live. It certainly isn't some National Code that's for sure. Although I agree that it would be best practice do vent outside, it's just not possible to do this on my 1970 2 story farm house. It's been vented between floor joists for all this time and I have replaced the fans and see no ill effects from this. No moisture, no mold, nothing.

 

[3Ts]

I found this and it goes back to the 2000 building code as well, probably farther. There is more info on size of exhaust pipe and distances, etc. in the building codes.


International Residential Code (IRC) 2012
Chapter 15 - Exhaust Systems
SECTION M1501 GENERAL
M1501.1 Outdoor discharge. The air removed by every mechanical exhaust system shall be discharged to the outdoors in accordance with Section M1506.2. Air shall not be exhausted into an attic, soffit, ridge vent or crawl space.

Exception: Whole-house ventilation-type attic fans that discharge into the attic space of dwelling units having private attics shall be permitted.

 

[EddieWalker]

What is a private attic?

 

[thekkfan]

What is a private attic?

One without rats, bats, or squirrels I guess. :laughing:

 

[outinthetalgrass]

One that is only over your house, as opposed to one that is open to both side of a duplex or several condos.