Bathroom Fan Venting Into the Attic?

21 Replies

I purchased a new exhaust fan for a bathroom that's never had one before. The guy I contacted to install it suggested ventilating into the attic, rather than externally, since the attic itself is already ventilated. Anyone have experience with this? He said it's a very common move, but I want to make sure it's not a shortcut that could lead to expensive problems (mold, etc.) down the road.

Vent it to the outside if you can. I had an exhaust BR fan that was vented into the attic when I bought a place, condensation from the fan led to water damage on the ceiling's drywall. I recently added ducting and vented it out on the roof, I did the installation myself with a $25 roof venting kit I bought off amazon that includes the roof vent and exhaust duct, it only took about an hour and was definitely worth it. I also believe in many places code won't allow it to be vented into the attic, but check what's acceptable in your area. 

Originally posted by @Kenny Fletcher :

 condensation from the fan led to water damage on the ceiling's drywall. 

 Same here ... 

I literally ran the venting up to one of the existing roof vent, 5 years no problems.

Find a more conscientious installer. It's not that much more work to do it right. 

New home building codes require them to vent outside. On my house they vent to the attic. It doesn't matter to me because I can't get my daughters to use the vent fans anyway.

For a well vented attic, it doesn't matter.

I had a personal residence where the existing owner had a fan venting into a ventilated attic (without my knowledge).  Upon selling the house, the buyer's inspector found mold on the insulation around the termination of the vent.  It wasn't a huge amount and I removed it myself filling less than one garbage bag of molded insulation, but the word "mold" in a home inspection report almost scared away my buyer.  An attic vent is a quick install and doesn't cost a lot of money - do it the right way.  

It doesn't matter how well ventilated your attic is - warm moist air from a bathroom hits cold air in the attic = condensation.

@Dave Haller If a contractor said this wasn't necessary, you need to find a new contractor!!

Venting the fan into the attic can cause many issues because of the moist air the fan removed from the bathroom. This moist air will cause condensation on the surfaces in your attic. This can not only cause mold, but damage to your roof system.

I purchased a home where the bathroom exhaust fans were vented into the attic and there was water dripping from the roofing nails that were protruding through the roof decking, causing them to rust! I didn't know this because the previous owner made it appear they were vented to the exterior by burying one end of the vent pipe in the insulation near the exhaust fan and running it to the soffit. I only caught it when I was installing more insulation and saw all the water dripping!

in my area you see many people venting the duct into the overhang (soffit), and having it facing down.  much easier to do than venting through the roof.

For bathroom vent..... outside. Always.

As a home inspector, I highly recommend always venting to the outside. Regardless if there is attic ventilation, there will be a good chance that mold can occur. Venting to the attic is a sign of a lazy installer, proceed with caution.

Agreed on all the above.  Last thing you want to do is take out moist air and trap it in a warm place, regardless of how well vented it is.  That is one of the thing I make sure to look for in any house I work in.  

Thanks for all the responses! That was my first Bigger Pockets post, and the community quickly showed me what a valuable resource it is. I plan to stick around.

I've decided to look for another installer, and will be sure to vent it externally. Today I poked my head into the attic for the first time, and the only access point is on the opposite side of the house. 

I do have a bathroom fan in an adjacent bathroom...anyone ever tried connecting the new ductwork into an existing one, 2-for-1? Just an idea, certainly not ideal, but might be a reasonable solution at a lower cost than cutting through the roof or wall.

@Dave Haller  

The other problem with venting into the attic is the potential moisture.  My first rental had a vented fan that broke connection.  The metal tubing was corroded and just looked crappy.  I had the owner replace it and reconnect it to the roof vent.  Home inspector caught it. 

Originally posted by @Kenny Fletcher :

Vent it to the outside if you can. I had an exhaust BR fan that was vented into the attic when I bought a place, condensation from the fan led to water damage on the ceiling's drywall. I recently added ducting and vented it out on the roof, I did the installation myself with a $25 roof venting kit I bought off amazon that includes the roof vent and exhaust duct, it only took about an hour and was definitely worth it. I also believe in many places code won't allow it to be vented into the attic, but check what's acceptable in your area. 

 We have a bathroom on an exterior wall with no venting other than a window in the shower.  On the bathroom exterior wall, below the roof, is an old school attic vent (vertical slats with wire mesh). Could I use that kit to vent a ceiling fan to that opening, instead of a roof vent?

In NJ where I am it is required to be vented outside..

Kristine Marie Poe There are also kits for venting outside on an exterior wall available online, and I believe that's preferable since there's less possibility for leaks. I didn't have the option since it is a rowhouse with a shared wall. However, I wouldn't necessarily recommend venting it through the attic vent, I think normally it needs its own vent. 

Originally posted by @Dave Haller :

... the only access point is on the opposite side of the house. 

...

Make sure that this is done using insulated ducting. 

Originally posted by @Steve Babiak :

...

Make sure that this is done using insulated ducting. 

Agree with Steve, if not you will have serious condensation issues venting it that far. 

I also would not connect the 2 together, you would more then likely depending on the runs of ducts end up venting one into the other.  

Originally posted by @Barry Cohen :

As a home inspector, I highly recommend always venting to the outside. Regardless if there is attic ventilation, there will be a good chance that mold can occur. Venting to the attic is a sign of a lazy installer, proceed with caution.

 Agree with you. Sound good. I will give it a try

Originally posted by @Dave Haller :

Thanks for all the responses! That was my first Bigger Pockets post, and the community quickly showed me what a valuable resource it is. I plan to stick around.

I've decided to look for another installer, and will be sure to vent it externally. Today I poked my head into the attic for the first time, and the only access point is on the opposite side of the house. 

I do have a bathroom exhaust fans in an adjacent bathroom...anyone ever tried connecting the new ductwork into an existing one, 2-for-1? Just an idea, certainly not ideal, but might be a reasonable solution at a lower cost than cutting through the roof or wall.

That's good, i'm new in forum too. I got many valuable resource from your

It's code to be vented outside. If not, moisture will cause a lot of problems in your attic. I would definitely find another contractor. It sounds like he didn't want to put the extra work in.

My bathroom fan in my new house was vented to attic, caused mold on the attic ceiling during the first winter.  You may not have that issue in Florida though.  I got a roof vent kit from home depot that included hose and roof cap for less than $30, and it took all of 30 minutes to install.  Well worth my time to do it right.

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