So much total GARBAGE

[tvrgeek]

OK, new bath fans. Top quality Panasonic 140 and 110 CFM fans. Really nice. So quiet you can barely tell they are on.
The morons who built my house ran 3 inch lines into the soffit. No vent. Got to fix that. I would prefer not putting J-Vents through the roof on the front of the house and well, I really should not be on the roof any more.
So, bought a 4 to 6 inch soffit vent for bath fans from Home Depot. Actual opening was less than the equivalent of a 3 inch duct. Dropped airflow to almost nothing. ( I am running 4" on the 110's and 6 on the 140) . Junk. Took them back. Bought a very expensive one , 4 to 6 inch spec, online that blows sideways so it does bot draft back into the attic. Good idea. Quality so bad the damper binds and won't close. Drops the airflow in half. Bought another that looked better from Lowes. Springs on damper were so stiff, the 110 CFM fan could not open them. More crap.

Why do companies make this stuff that flat does not work for the intended use? Do most people just put them up and not know they don't work? I explained to Home Depot the product by definition could not work as intended and all they wanted to know is if they were still unused and able to re-sell!

Not sure what I am going to do. I guess roof J vents on the back for the two small fans, but that much duct for the big fan would be a serious drop. Hate to put it on the front of the house, but about out of options. That is IF I can get a vent that is not garbage itself. Not impressed with the ones from Blue and Orange.

 

[Rwe2156]

I would not go through the roof.

I haven't installed a hundred of them, but I've had good luck with Broan.

 

[tvrgeek]

Yes, Broan makes high end fans along with their contractor grade. The Panasonic fans are comparable or a step up.

Making a test. I took half the grill out of a Lowe's vent, cut out the damper as the Panasonic damper is pretty good, glued in a screen and hooked it up. I'll see how well it does when I take a shower tonight. It does have about a 6 inch open area but restricted some by a grill and screen so probably OK for the 4 inch fans. My alternative is to make a box that hangs under the eve with sufficient grills on it. Ugly, but not as ugly as a roof vent.

Of course, if this was not a hip roof, I would have gable end walls to go through and things would be a ton easier.

 

[junquecol]

Yes, Broan makes high end fans along with their contractor grade. The Panasonic fans are comparable or a step up.

Making a test. I took half the grill out of a Lowe's vent, cut out the damper as the Panasonic damper is pretty good, glued in a screen and hooked it up. I'll see how well it does when I take a shower tonight. It does have about a 6 inch open area but restricted some by a grill and screen so probably OK for the 4 inch fans. My alternative is to make a box that hangs under the eve with sufficient grills on it. Ugly, but not as ugly as a roof vent.

Of course, if this was not a hip roof, I would have gable end walls to go through and things would be a ton easier.

Soffit vents will always draft back into attic. In working years replaced several which had drafted back into attic, causing plywood to ROT on that truss / rafter bay. Moisture went up to peak before spreading out.

 

[tvrgeek]

I have a hard time really believing that as a guaranteed outcome. First, my fans have sufficient velocity to push out into the air stream. Maybe I could believe it with the vents from Home Depot that reduced the flow in half, diffused to the circumference, and starting with a contractor 70 CFM fan into a 3 inch corrugated duct where you had 10 CFM at the vent. Secondly, for there to be that much back-draft, it would be a hot summer day with totally still air and and so there would be no condensation. If a prevailing wind against that side of the house I could see some diluted back draft. Maybe on a really windy winter night where the ridge vent was acting like a siphon then it could make it's way back up and condense. I can feel a draft from the ground for the one I just did.

Now back draft is the advertisement the extended vent manufacturer claims. If had not been warped and was about two inches taller for sufficient cross-section, with proper channeling of the air for the right angle turn, then it would be a good solution. I have to believe there was no real testing of the design. Good idea, not gone far enough, and not a thorough enough design for the materials and processing to make a reliable product, I would be putting on three of them, not sending one back. Even as they cost twice the price as the Lowes and HD vents, I would go that route.

I am starting with the ducts just stuffed INSIDE the soffit bay. It has been that way for 30 years and only the slightest hint of condensation/mold.

 

[mkepke]

I also wouldn't cut holes in the roof for vents, but I'm lucky to have gable walls.

I've also replaced two of three builder's grade fans at this point. One was like Scott's: a cheapo 3" vinyl flex duct running to the soffit (but not actually vented outside). The other was worse..it just vented to the attic via the ceiling joist cavity..except the cavity was filled with insulation. No rot - go figure.

I replaced them both with Broan AE110s on insulated 4" lines running to new sidewall vents. I ended up special ordering the sidewall vents themselves because the in-store options were terrible.

-Mark

 

[Oka]

I have installed so many of these over the years.
Some simple guidelines a on any duct for a bath 80-200 cfm. 4 or 5 " is typical. Going bigger tends to affect the flow characteristics. If it was a supply feeding air in , then yes larger would lower the static resistance. However, in exhaust you want the flow to not dissipate in strength until the end of the duct or it could affect potential efficiency.

An example - if you have a typical bath room usually is around 45-60 sq ft. so let's go with a 7x9 room, 9 ft ceiling

7x9x9=567cu ft. So, if you have a 100 cfm fan, it would take about 6 min to totally exchange the air, or 10 air exchanges per hour. anything above 6 would be considered excellent performance.

Bit of a factoid. Typical fans or sellers will loudness in sones and will say "only 1.8 sones"

1 sone = 28db
2 sones 38db (37.99)
3 sones =44db (43.84)
4 sones = 48db (47.99)

A good fan runs about 1 buck a cfm for estimating purposes. Most bath fans are cheap and not worth the cost. I found a bath fan on Amazon that was a .7 sone fan (26 db) for 130 bucks, nice unit running for 3 years now no issues.

To provide a comparison: a typical computer tower fan is a bout 20 db

Finally, 3- 20 db fans running together at the same time is still 20db ...it will still be 20 db in sound level.

 

[tvrgeek]

Yup, cheap fans are crap. Happy with the Panasonics. It is the soffit vents that are garbage I was referring to for this thread. Of course, production builders use 70 CFM fans and 3 inch corrugated dusts because code lets them. I can't believe code should have let the ducts end in the soffit in '92 when my house was built, but it has a lot of things that should not have passed. Missing handrails on front steps, no caps on chimney, brick window sills not weather proof...

With a long shower, the new fan and duct almost keep the mirrors dry. Big difference. Unfortunately the duct is about 12 feet long as I wanted the fan closer to the source ( shower) than the outside wall. Another problem is many houses is the fan is too far from the source. Only issue with the Panasonic is the inside grill is too restrictive. Easy fix. Difference is measurable with my aerometer. I am looking for about 100 cfm actual installed system so the 140 cfm fan seems to be the correct unit. The half bath and guest bath I can deal with a lot less so I bought the 110 CFM Panasonics.

I disagree a little with your in vs. out conclusion for a bath fan. In either case it is just about moving a volume of air. At least by the fluid dynamics I have taken. Totally agree in a dryer exhaust as too low a velocity increases the dust drop-out in the duct. Bad news. Same issue with our shop dust collectors. Grangers used to have really good duct design guides, but now we do better on Dust Collector like ClearView WEB sites. Of course, you probably have access to ACCA guidelines. I think they want actual money for their manuals.