Bathroom Exhaust Fan Ductwork

A discussion of bath exhaust fan duct work options and important details. Make sure your bath fan is vented properly to avoid mold, mildew and other issues.

[@dandanpete]

8 years later and your video is still helping people. Thank you so much.

[@enduringcharm]

Glad it helped!

[@austinbarger7785]

Great video. Detailed information like this is becoming harder and harder to find.

[@shakirahmedtth]

What a great demonstration on paper.. Thank you, Sir.

[@cesarmendez5031]

I do Duct Cleaning and also install duct (both a/c and dryer/bathroom ) and the best duct that you can use will be the metal one without grooves. We clean a lot of Bird Nest out of exhaust vents and whenever we find the plastic or the flexible metal one we always replace it because is damage, solid metal duct we clean

[@enduringcharm]

cesar mendez I agree--smooth wall metal duct is the best choice when possible.

[@mrnetwurm]

Thanks, this is just the info I was looking for. I've had trouble with condensation dripping back into the fan. I never thought of insulating the pipe.

[@enduringcharm]

It is amazing how much water can be generated by condensation.

[@paulgreco6824]

The roof vents are a good idea in theory, however in my experience, ive seen far more issues with CT4 roof vents compared to soffit venting. In a cold snowy climate, the roof vents get buried, cause ice damming and cause condensation to run back down the duct, instead of out the vent such as in soffit venting. Placing the vent higher on the roof only exacerbates the issue of condensation running down the vent and believe me - that insulstion sock with its R4 doesn't do much when its in the -20 C range outside. If you do use them they shoud be placed low to maximize the amount of pipe that can be covered with attic insulation. A drip trap in the duct helps, but the bottom line is the water is still coming in instead of going out. Ive removed roof vent ducting that had LITERS of water trapped in them! Blocking the vented soffit with some vapour barrier 2 truss spacings on either side solves the issue of moisture re entering the attic.

[@enduringcharm]

Paul G Sounds like you're in a pretty cold climate! I've personally installed maybe two or three dozen roof vents for baths in our New Jersey area. Before I started using insulated ducting I had one client get some water/ice in the duct during a very cold period. Now that I use the insulated ducting I've had no issues even though we've had extended periods of 0-10 degree F weather. Obviously, though, you have to use some common sense and take into consideration the climate and the house structure of each installation. If I see something unusual or worrisome in a particular house I'll look for alternative venting. In my area snow blockage hasn't been a problem, but I could certainly understand that in other areas that may not be the case.

[@justanotherbum007]

Paul 81 I just moved to the Western Slope a few miles from the Continental divide (lots of snow). The home I live in has soffit venting for both bathroom fans.

[@enduringcharm]

I was just re-reading this thread. The 2012 IRC, which just recently became code in my area, does now address soffit venting. Here's the quote: 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. In addition, air can't be exhausted within three feet of a building opening (like a window). Different jurisdictions may have different codes or interpretations, but in my area new installations will have to be through the roof or possibly through a gable end if one exists.

[@pietrosammarco6225]

@@enduringcharm "Air shall not be exhausted **into** a soffit" -- sounds to me like that's not the same thing as exhausting **through** the soffit. "Into" means into the soffit cavity itself, doesn't it?

[@enduringcharm]

@@pietrosammarco6225 Exhausting through the soffit, as you point out, may be allowed in some areas. However, it doesn't change the problem. If you have soffit vents AND a ridge vent or gable vents, then there is a chimney effect created which pulls air through the soffits and upwards. That's the whole point of roof venting. In doing so, moist air which is exhausted through the soffits will just be drawn right back in. That defeats the point of an exhaust vent in the first place. The best method is still through the roof or, in heavy snow country, through a gable wall if you prefer.

[@enduringcharm]

Siniestro02, you can often link two fans into one vent but make certain each fan has a backdraft flapper and that the vent has enough capacity for both fans at once.

[@enduringcharm]

I see that often. Ideally you should go through the roof or through a side wall, but if your roof does not have both soffit and ridge vents then there isn't that much air going through the soffit vents alone. Installing a vent plate would be a marginal improvement. But, if you do have both soffit and ridge vents, I'd urge you to get a roof kit and just do it right.

[@u235u235u235]

my tile guy just installed a bathroom fan and it's venting directly to my attic space (ranch home) without any duct work. He told me it should be fine cause my attic has vents along the soffit. Is this OK? One two people showing in the house daily, taking 5-10 min showers. I live in the northeast US and have winters and summers.

[@enduringcharm]

***** No, it's not okay. Your tile guy should stick to tile! It must be vented to the outdoors no matter what kind of house and you run the risk of mold, mildew, soggy insulation and eventually rot in warm periods as well as gathering ice in cold periods that can drip back in the house when it warms up again. And, yes, I have personally seen all of these things in New Jersey attics where I work that have not been properly vented. When I visit clients for bathroom remodels a properly vented fan is one of the items I look for and I put it in the estimate if it hasn't been done right. You need to have a pro install ducting to the outside, ideally through the roof if possible.

[@laurentampa2054]

Very helpful! Thank you!

[@Engineria]

Great, just what I needed to know

[@san379]

i like using the insul sock and the rigid ductwork and adjustable elbows and tin tape all joints and go through the roof or the gable end but the roof you need a CT4 vent from the MAXIMUM COMPANY ..MADE IN QUEBEC CANADA.. WHERE WE GET 4 FEET OF SNOW

[@aurorablusky]

Good start to a longer topic. For example, I'm installing an in-line/remote exhaust system in my bathroom and want to use either PVC or metal duct. The problem with PVC is in the sizing, sorted by inner diameter (e.g. 4", 6", etc). It doesn't fit any of the remote fans without a rubber gasket or improper installation. When looking at metal, it's smart to go with stainless, especially when dealing with high humidity environments. Finally, after you've chosen a material and verified fittings, you have to make sure you've calculated static pressure to ensure you have the suction you need in the room you need it in. In order to really do it "right," you have to turn something pedestrian like installing a bathroom fan into something a little more HVAC-oriented. Bottom line, would you consider discussing additional topics like solid duct materials, determining duct size, and run length?

[@enduringcharm]

+Aaron Boyle You're right, the topic can get complicated pretty fast. There is a theory about PVC ductwork that says static electricity can build up during air flow. That's why woodshops don't use it for dust collection, because the sawdust in the collection system could combust. I've never used it for bath venting either, and you have already discovered one reason why! Lately I've been using flexible/insulated ductwork like what is used in AC systems. It's fine for short runs and the insulation prevents ice from building up in the winter. For longer runs I typically use aluminum duct that I also insulate. Foil tape is used to seal the connections. Every fan manufacturer has it's own requirements for length and bends, etc. For short runs it's not critical, but for longer runs it's best to look up the spec sheet.

[@anitadsouza1335]

Could you produce a short video on repairing the roof after the B50's have been physically removed from the roof ? My Roofer removed the B50's and just hammered on a layer of shingles (there is no 1" x 8" wood underneath so roof just has a layer of new shingles in spot where the B50's previously located). Roofer tried to shake me down for more $$$ after installing the Maxi-Vents but I wouldn't balk. Should I spray foam the underside of the roof where the B50's previously located while in the Attic ?

[@enduringcharm]

+anita dsouza If you are removing a roof penetration of any sort the correct way to make the repair is to replace the roof sheathing underneath the shingles, going at least to the nearest two rafters. Then you would reroof as necessary. If the hole your roofer shingled over is relatively small you may get away without sheathing underneath if you don't have heavy snow loads. But, it isn't the right way of doing it.

[@mikethk]

PERFECT PERFECT PERFECT............................................. You made my day x 12

[@tugger]

perfectly informative

[@michellebardwell3249]

My husband and I just replaced our bathroom fan and it started dripping when we used it. We did fill the area around it with standard insulation but it is still dripping. we checked the damper door and it is working properly. Any thoughts on next steps?

[@enduringcharm]

I'd need more information to venture a guess. Common problems include stuck damper doors on either the fan or the exhaust vent to the exterior, a vent pipe or tube which is clogged or kinked or too long, an uninsulated vent pipe or tube which leads to a dew point inside, etc. All you can do is physically check the system at each step.

[@bg147]

I installed a new old stock Leigh chrome exhaust fan in my kitchen. It is ready to be vented. The plan is to run it our the side wall and the fan is the 10 inch model. I could run 10 inch round or reduce it to 8 or 6. The benefit of reducing is a smaller wall cap. What would you do? This is a little 8 x 9 kitchen in a 100 year old house and I don't need massive ventilation, but it is a 10, and my inclination is just to run all 10. Thank you.

[@enduringcharm]

Well, look. The variables to think about are the CFM of the fan, the duct run distance and the duct size. You don't mention the CFM rating of the fan and maybe you don't even know what it is. In modern fans 400 CFM is the cutoff in the newest building codes for needing a makeup air device of some sort installed, and there are many fans now being built below that cutoff so as to avoid triggering a code compliance issue. I would guess your vintage fan is under that, but I'm not sure. Anyway, if I have the right fan in mind, there really is no ductwork, right? In other words, this mounts on a sidewall and vents directly to the outdoors? If so, then the duct length variable can be ignored and it's really just a matter of size. That 10 inch fan may be a low velocity design which makes up for the low power with a big opening. My seat of the pants advice is that a six inch opening is likely much too small, especially since the airflow originates mostly from the tips of the fan blades, which wouldn't leave much room if this is just a four inch duct run through the wall! An 8 inch opening you might get away with, but it wouldn't hurt to do a test before you install it. Another thought I have is that you might be able to replace the guts of the fan with a modern improvement. In other words, keep the interior grill and look that you want, but retrofit a modern exhaust fan behind the grill so that you actually have some manufacturer specs to use.

[@bg147]

@@enduringcharm That all makes sense. I will stay with the 10 inch. Save money on a reducer and get better flow. The house is a 100 years old and never had an exhaust fan in any of the rooms. The retrofit down the line is an option. Yet, the kitchen fan moves a lot of air. I think it has 10 blades I have a photo. For me, it is about the look and authenticity. I just installed mine in the ceiling and it has a deep housing along with a gravity damper. Someone told me it is a wall unit but the damper is gravity operated, so, he changed his mind. I was going to run it through the roof but due to the chimney being inches away, I will run it out the wall in the attic. The photo with the yellow wall is the kitchen. Thanks again. facebook.com/bruce.garibotti/posts/10157999624690470

[@enduringcharm]

Okay, I see you've mounted it in the ceiling, not the wall, and there is some length to the duct. Probably you could have gone with 8 inch duct, which would increase velocity and perhaps help keep the duct clear of grease over time. One other thing I'll mention is that you may want/need to insulate that duct in the attic if you are in a cold winter climate. It's more critical with bath fans due to the excessive moisture, but it could become an issue with kitchens as well. When moisture goes from the warm interior and hits that cold duct in the winter, it condenses and can actually freeze before it gets to the outdoors. Since you are using a vintage fan without specs to work from, just keep an eye on it for a season and see how well it clears or if it has any of the issues we've discussed. You can always modify it later if need be.

[@bg147]

@@enduringcharm Thank you. In the bathroom I dropped down to 6 inch duct for space and cost reasons. It is more than I need. In the kitchen, I haven't vented it yet but have been leaning towards 10 inch duct and will use smooth duct. Thank you for the information about insulating. Never thought about that.

[@PlumbingPredator]

Hi! Would it be better to have to flexible metal pipe + the insulation cover over it instead of just the flexible plastic pipe + insulation? ( for bathroom vent)

[@enduringcharm]

As far as internal resistance to airflow, the flexible aluminum pipe is likely not much different than plastic, though it probably is a little stronger. The advantage of the plastic is that it comes with insulation already installed. The best airflow is attained through solid metal pipe, which would then need to be wrapped in insulation for a long run. I try to keep the vent runs as short as possible, which means that the flexible plastic pipe is fine.

[@saintkocila5171]

Thank you for sharing.

[@larryscarberry7316]

I have a soffit that is solid aluminum with no venting. In that situation, would venting to the soffit be ok and produce the moisture being drawn back into the attic?

[@enduringcharm]

Larry Scarberry I still prefer roof or gable end venting, but in the situation you describe the moisture would not be drawn back into the attic or the house if no windows are located nearby. However, there could still be long term issues with moisture in the area under or around the soffit causing decay.

[@larryscarberry7316]

enduringcharm Thanks for your input! Very much appreciated!

[@turboflush]

only vent through soffit or wall if far enough away from any roof vents. otherwise.. it needs to go through the roof. Roofs require maintenance no matter what.

[@Rock-wy6ih]

Great vid man! Thanks for posting! X-Jersey guy here now living in CO. Any advice on how to exhaust an 8'X5' bathroom with a cathedral ceiling and a 2'X4' skylight centered in the room? I was gonna do a 90CFM fan above the skylight closer to the ridge and vent thru the roof hoping the higher height would help keep the skylight free from condensation. Only drawback about going thru the roof is I'm dealing with 2X6 rafters so not a lot of space for insulation.. Any advice would be appreciated! Thanks!

[@enduringcharm]

+Rock 36 It's pretty tough to offer this kind of advice from a distance. 2x6 rafters offer little flexibility, you are right. Sometimes in cases like this a remote fan can be located elsewhere and just the duct work fits in the rafter bay, but you may not have access to this ceiling from another part of an attic. Rigid foam board insulation offers a very high insulating value per inch, but I doubt you'd have room for that near the fan unless you go straight out the roof with the fan. I suppose you could build the ceiling down by stripping off the drywall, insulating in the rafter bays (allowing for ridge venting if you have it or else using spray foam) and then using foam board insulation to pack down the rafter edges by two inches before applying the drywall with long screws. That would buy you some room, perhaps. I dunno--tough one!

[@tommyboy53940]

+Rock 36 I have a stupid question. Can the exhaust duct be hooked into the stink pipe via a sanitary tee fitting?Just don't have any other way I can find to vent it from my circa 1875 home.

[@tommyboy53940]

+Tom Baldi It's on 2nd floor bathroom and I would attach it right before the stink pipe goes through roof. Any other area would make the duct run too long for the fan to move the air/moisture properly.

[@enduringcharm]

Tom Baldi That's a big no-no to try and connect your exhaust fan into the plumbing vents. Those are two different systems designed for different reasons and never should the two meet. If for some reason you can't get your exhaust vent through the roof, you can look for a gable sidewall or a soffit as last resort. There are remote mounted fans that offer longer runs because the fan itself is located in the attic space and the intake from the bath is just a four inch hose. Panasonic makes some. There are also booster fans available which allow for very long runs.

[@jbw5485]

Great video. But what do you do when you're in a 2 story house? I have a fan/light but there is no duct work. It doesn't remove the moist air to anywhere. Just a fan spinning. One side of Bathroom is exterior wall first floor with the roof line/ soffit down level with the first floor ceiling. Only problem running it that way is its not with the floor joist. I would have to cut and run duct through each joist. Thanks for the video.

[@enduringcharm]

***** Now you know why the original installer just left the fan with no ductwork! For first floor bathrooms there needs to be forethought in the planning for the ductwork, just as there should be for plumbing drains and other factors that must be framed around. Since they didn't do that in your case, you may have a n insurmountable problem. If you have an exterior wall you can install a sidewall fan that vents directly to the exterior through the wall. It's not the prettiest looking thing, but it may be better than nothing.

[@jbw5485]

enduringcharm thanks for the reply. Is it still an option if it's a brick wall?

[@enduringcharm]

***** Boy, you have all the luck, huh? Yes, even with a brick wall it can be done, but you'll probably have some trouble finding somebody to do it. You may need to find a mason and a carpenter and an electrician on your own if you can't find a single contractor to handle the job.

[@shawnhill4779]

Not quite right. In areas of significant snowfall in the winter months, your first choice should be venting out the gable end of a house. Second choice is to vent out the soffit. Venting out the roof should ONLY be considered as the 3rd choice due to the potential for ice dams starting on the roof.

[@josephryan8788]

Can Bathroom fans be vented into a PVC stack pipe with PVC?

[@enduringcharm]

Do you mean vent the exhaust fan into the plumbing vent stack? No, that would be a huge code violation and a bad idea. You'd have a path for sewer gas to reach the inside and you'd be putting the plumbing stack under pressure when the fan is running. If, instead, you are asking about using PVC as ductwork, that is also a bad idea. While it may be a remote danger, PVC is known to build up static electricity with airflow which could present a fire hazard. Plus, exhaust fans are designed to work with the diameters of metal duct.

[@kevingomez5689]

Can you connect 2 exhaust vent to rhe same pipe?

[@enduringcharm]

That's a qualified "yes." Just make sure you have enough capacity to handle both feeds into one. Two 4" ducts into a single 6" exhaust will work, for example, though some efficiency will be lost when running simultaneously.

[@siniestro0239]

it's hard to find well made videos like this. thank you it helped a lot. one question. can I attached two bathroom fans to one of this vents or do I have to get one vent for each bathroom exhaust fan? thank you

[@aurorablusky]

PS- I stumped a veteran HVAC installer (25+ years) who's never installed a remote/in-line exhaust fan because I wanted to do it the "right" way, not the contractor-grade way. It was quite frustrating, anyway, having and obvious way to bridge the gap between a 4" inner diameter for PVC and a 3 7/8" outer diameter for a fan collar. May just suck it up and install with insulated flexiduct.

[@tundeuk]

How long is a “long run”

[@enduringcharm]

Every fan has a rating for length in the paperwork somewhere, and things like elbows and duct type have an effect on that rating as well. You need to check what the manufacturer specifies as far as how long a run you can connect to a particular fan. As far as insulation, I fully insulate every inch of duct in my area, which gets cold winter weather. In warm weather areas this may not be necessary.