Venting a bathroom: Looking for suggestions

First time poster, long time lurker, finally joined after reading [thread=450485]why the SDMB is special[/thread]. I was amazed at the advice given to the folks who were [thread=442734]trying to run some cable through their walls[/thread], and have a house quandary for which I’m seeking advice. Apologies in advance for my verbosity.

My SigOth and I bought a place together this summer, and I’ve been chipping away at projects I’m capable of tackling. One task was replacing the bathroom fan which (a) was wimpy and (2) vented into the attic. We had a louvered vent with a 4 inch stem installed. I bought a fan with double the cfm (90 vs. 180) and a 4 inch flex hose. Not being the brightest man in the world, I didn’t notice the fan I’d chosen had an 8 inch exhaust until I’d gotten half way through the installation. But I soldiered on, got it connected, then went to my local non-big-box hardware store and got a couple decreasers, 8 inch to 6, and 6 to 4 . Stacked 'em on top of the exhaust, taped them down (first time I’ve ever used duct tape on ducts (I know some people call it duck tape, but until I need to tape a duck I’ll call it duct tape)), taped the hose to the decreasers and to the new vent (about 3 diagonal feet from being centered on the fan), congratulated myself on a job well done, and put my tools away.

While it worked, it didn’t work well, and using some squares of TP, I realized that a lot of air was blowing back into the bathroom. “Suffering Succotash!” I thought to myself (with a bit of blasphemy in place of the first word and a term for excrement in place of the second). My guess was that the decreasers were was forcing some of the air to reverse. So I went shopping for an 8 inch vent hose (which was hard to find, and not cheap, but I found some on the web).

When the new hose was delivered, I grabbed my tools, and set to dismantling my first attempt (which was kinda sad because, frankly, the two stacked decreasers with the hose coming out the top just looked cool, almost Star Wars droid-esque). After failing at a not-so-clever attempt to hang the decreasers from the rafters, I taped the 8 inch hose to the fan (using string to suspend it so there was as long a straight run as possible (about 2 feet)), let it curve back to the joist level, connected it to the decreasers, those to the 4 inch hose, and finally to the vent.

So, it works much better. But I was hoping for more. Like never having a fogged-up mirror or wet walls. We run it for 10-20 minutes after showering, and that clears everything up (eventually we’ll get a timer switch).

Here are my questions:
[li]Short of having an 8 inch vent installed right above the fan, what can I do to increase the performance?[/li][li]Is the fan powerful enough? (The bathroom is about 60 sq ft.)[/li][li]Are my no-fog dreams destined to remain unfulfilled?[/li][/ul]

Thanks in advance to the responders.

I don’t understand why you don’t want to vent it to the attic. The attic space itself is (or certainly should be) adequately ventilated and adding a few hundred cfm occasionally won’t make an appreciable difference. AFAIK, building codes do not require exterior venting for residential bathroom exhausts.

All that aside, it’s the reducers that are the problem. That and the louvered vent are creating considerable resistance to flow. If you have gable vents, direct the exhaust hose out one of those. You’ll get better airflow and you’ll be venting to the outside. If you don’t have gable vents, then you should look into installing some type of attic ventilation, such as turbines or powered ventilators, to help with your summertime cooling bills.

Rhubarb, venting into the attic is shunned because the humid air can cause mold to grow.

uncle squeegee, could you post pictures of the vent location, the attic above and the eave closest to the bathroom?

Thanks, cornflakes, it’s not an issue where I live. Bathroom fans are typically vented to the attic here.

Still, the duct reduction is the main problem. Venting through a gable or re-fitting a soffit vent with an 8" boot would resolve that.
There’s also the option of using a remote mounted fan such as this. Higher cfm, lower noise and consumes less power than a standard 180 cfm bath exhaust. It just costs a lot more upfront.

According to my references, 2003 IRC requires bathroom fan ducting to vent to the exterior under section 303.3 and the 2003 UMC requires the same under section 504.1

Venting via gables, soffit, or ridge caps (e.g. pressurizing the attic) is/are prohibited.

Thanks. My last UMC is the 1987 edition :o . So I guess uncle squeegee is left with a.) living with his current installation or b.) installing a roof jack or 8" sidewall vent.

You’re welcome. Those are the only options I see, too. From what I’ve observed, IAQ has become a hot topic, and many of the things ‘we used to do’ are now verboten.

Yeah, 8" roof jack or sidewall vent, whatever’s closest. Check the Yellow Pages for “Sheet Metal Equipment and Supplies” to find a source.

One thing about Duct Tape. Use it (a la Red Green) to make a sauna cabinet out of a broken washing machine, but don’t put it on your ducts. After a few years, the adhesive fails, the tape hardens up, and it falls off like the husk off a cicada. Instead, buy foil tape. It should be in the store right next to the duct pipes. There is a peel-off paper backing, the adhesive is long-lasting, and the tape confirms nicely to the pipe.

Flex duct decreases flow,and should be of last resort.Straight runs of it are OK,properly supported.Turning is best done with metal,unless you have the room for long radii using flex.In a cold climate it all needs insulating.The fan manufacturer should supply tabling for the maximum length of run.Remember any turn equals multi feet.
I have the Aldes (pictured in the Grainger link above) which provides 100cfm per port.The bathrooms it serves are about the same size as yours;with the timer set at 15 minutes we get no fogged mirrors.That may have to do with strategic suction placement though.

You mention that you’re running it for 10-20 mins after a shower, but do you run it during the shower? If you run it during the shower, you will probably have a dry (and cold) bathroom when you are done showering, and any remaining moisture will be gone soon after that. Now, if you’re like me and don’t like getting out of the shower into a cold bathroom. Here’s a trick. Set the timer for a few minutes less then your shower. So…as soon as you walk in the bathroom and flip the water on, turn on the fan. When you’re ready to get in to the shower set the fan for about 3-5 minutes LESS then how long you think you’ll be in there. That gives you just a little heat and moisture so it’s not as much as a shock when you jump out. Then, as soon as you get out, turn the fan back on.

Personally, I’d like to set up a series of timers, one normally on, and one normally off, wired correctly, so that it will turn the fan ON about 5 minutes before I’m done rather then the other way around. But I think that would be confusing to everyone else.

Just gotta say, I’m an electrician and have hooked up hundreds of bathroom fans and have never seen one with an 8" exhaust. Not for a residence, anyway. Restaurant and commercial bathrooms, yes, but not a home. Are you sure you’ve not bought a 220 volt fan? Check the package or the fan itself (if you can still get to it) and see what voltage this thing needs. Or link the model number.
A fan with an 8" exhaust should pull the wallpaper off the walls.

slight hijack, since the experts seem to have gathered - the exhaust fan in my main bath vents into the soffit space in the attic via a 3’ length of 4" flexible tubing. The house is about 5 years old, so I don’t know if that was code then, or if the builder loosely interpreted “venting to the outside”. Is that something I should worry about/do something about? I’ve never observed any mold in the attic, and the fan does get used for 2 showers a day.


Man, this is the next job I have ahead of me. Got a wimpy little fan with a 3" exhaust venting into the attic. Just not holding up to those teenagers’ half-hour steam baths!

Tho the attic is well vented and shows no sign of mold, the responsible thing is to run the vent ~ 15’ to the side wall.

My house has a peaked roof. The 2 ends each have a large (~ 2’x2’) louvered vent, in addition to vents on the roof and under the eaves. Would it be okay to just run the fan exhaust up to the existing sidewall vent, or need I punch a new hole through the wall? (I know what the right answer is, just trying to convince myself I can “get away with” the easier route.)

What he said.

Typically when installing a new roof, to bring the existing house up to code, we vent directly up, using a louvered vent like this. You can also see an example of a wall vent.,GGGL:2006-41,GGGL:en%26sa%3DG

Ideally, what you would like is the proper exhaust vent to prevent insects and animals from taking up residence in the venting. You should install a flapped exterior exhaust vent to prevent any backflow into your venting and to keep out the critters.
You want to get all that moisture out of the house and attic.

Plus, you don’t want farts accumulating in the attic, do you?

Here in the Northeast attics are ideally constructed with ridge (or other) vents so that attic space is the same as outside air. One concern (in addition to mold) is that humid air venting into the attic in the winter will condense and saturate the attic insulation. This can lead to ceiling staining, possible rot, and the effectiveness of the insulation is reduced.

That said, my bathroom contractor assured me that there was no problem whatsoever in venting to the attic. I had to put a vent through the soffit myself, and he connected the fan exhaust to it. My bathroom is about 70 sf, and I have a four inch fan. I can’t remember who made it, but it is pretty much off-the-shelf. I turn it on when in the shower; when I get out I wave a towel a few times to get convection going and the fog goes away quickly.

I agree that putting reducers on the fan exhaust will reduce its effectiveness and could potentially shorten its life. And 8 inch seems to be more than necessary; a 4 inch should be plenty. I think the two choices are to either to install an 8 inch vent, or to replace the fan with a smaller size.

Attic rule: Okay, venting into an attic is **not **best practice. So, while you might offer anecdotal evidence that it is fine for you (Hey, y’all, I ain’t see no mold yet!), there are also people out there who have improperly wired homes that didn’t burn down yesterday.

When you break a rule of best practice in home building and home repair, it doesn’t guarantee anything, but you increase the odds of the ‘bad thing’ happening.

Vent moist air into the attic and you INCREASE the chance for mold. Wire a fixture improperly and you INCREASE the chance for a fire.

Wow, I get into work and have a lot of good suggestions, Thanks all for your time.

cornflakes (post 3): My camera is on the fritz, so photos are not an option currently (and due to some social commitments, I probably couldn’t even get to it until about 10 PT tonight). The bathroom is almost centered between the gables, so going out a gable is not an option.
Pel2na (post 8): Thanks for the tape tip. I’ll add foil tape to my shopping list and do some re-taping soon.
Joey P (post 10) : I didn’t quite understand what you meant until I noticed you were in Milwaukee I do run it during the shower. It rarely gets below freezing in Seattle so a cold bathroom isn’t a major problem. But I like your thinking.

Uncommon Sense (post 11): It’s a Broan model 505. The manual didn’t say anything about 220, but I’ll check it again to be sure.

A roof jack is looking like the best option as suggested by Rhubarb in post 6.

It’s definitely a 120 volt model. 180 CFM is going to evacuate that bathroom in a hurry. That’s why the 8" duct, most homes don’t have a fan with that much flow in their baths - that’s why I haven’t seen 'em.

Carry on.

Yet another datapoint confirming my opinion on the worthlessness of property inspections. When we bought the house 12 years ago, we knew it needed a new roof, and had one put on soon thereafter. If the inspector had mentioned anything about this, it would have been simple to just have a roof vent installed at that time.