OT- Five bathroom exhaust vents with the flex hose terminating into one manifold at the roof vent ...is this normal ?

[Milacron]

Moved into new townhouse (2010 construction) a few months ago and just now noticing a vent issue due to mold forming on vents. The vents have impressive looking fans, but draw very little air (test with strip of toilet paper right at the vent and paper barely moves). So wondering if the problem is the manifold concept is a bad design or a stuck damper on the roof vent ? (which I would have checked already but due to roof pitch and height I'd be risking my life )

 

[DDoug]

I ask as the vents have impressive looking fans, but draw very little air (test with strip of toilet paper right at the vent and paper barely moves). So wondering if the problem is bad design or a stuck damper on the roof vent ? (which I would have checked already but due to roof pitch and height I'd be risking my life just to do so !

Flex hose is a bodge job.
It restricts too much, collects moisture, etc.
Are these the standard 4" dia ?
What dia. is the manifold ?

 

[adh2000]

Totally normal construction we see it all the time around here. However there needs to be more than a damper at the roof. There should be a larger fan at the roof to guarantee negative pressure in the manifold at all times. A Dwyer differential pressure guage (available on ebay for like $10) would tell you immediately what is going on. Of course connecting the tubing to the gauge is a gigantic pain.

 

[cnctoolcat]

Inside the attic you might be able to take all the flex hose loose from the roof vent, then see if anything is up with the vent? I would replace the flex hose with proper solid pipe, pvc or metal per code...

ToolCat

 

[DDoug]

Sound like it's time for 440 vac 3 phase in the house eh ?

 

[APD]

Moved into new townhouse (2010 construction) a few months ago and just now noticing a vent issue due to mold forming on vents. The vents have impressive looking fans, but draw very little air (test with strip of toilet paper right at the vent and paper barely moves). So wondering if the problem is the manifold concept is a bad design or a stuck damper on the roof vent ? (which I would have checked already but due to roof pitch and height I'd be risking my life )

They make remote fans that are installed in the attic and can handle multiple bathrooms. They are usually much quieter than having a fan in each bathroom.
Each fan usually has its own damper which could also be stuck.

 

[GregSY]

It's very common here to see bathroom fans, one per bathroom, with the flex hose routed into the attic then left connected to nothing.

On the topic of vents, my piece of shit Kenmore dryer 'refused' to vent properly through the 12" long duct that passes through the wall. The low air flow would allow the gas burner to overheat, which would then turn off. So...you'd run a load of clothes for 60 minutes and they'd still be very damp when the timer shut off. I added a separate induced draft fan that sits external to the dryer and turns on when the dryer is started. It mega-vents the dryer and now I can dry a full load of wet shop towels in about 30 minutes.

 

[Scottl]

Can you disconnect the manifold so you can check the roof damper from the inside?

All things being equal I suspect the manifold setup is diffusing airflow to the other hoses unless it is a "Y" construction with relatively steep angles.

Update: I did a quick search and general consensus is that the only way to vent multiple bathrooms through one vent is by using an inline fan AFTER the junction so the air is drawn from it as per this article.

How to Use an In-Line Exhaust Fan to Vent Two Bathrooms

Venting two bathroom exhaust fans through one roof duct won't work. But you can install one fan in your attic for both bathrooms.

www.familyhandyman.com

 

[Bill D]

Note the steep angle of the tee fitting. It is really a Y fitting.
Bill D

 

[L Vanice]

My 1974 house has three bathroom fans that each have a foot or so of flex hose that gets the exhaust out above the glass insulation. It works. The attic has soffit vents and ridge vents, but no forced ventilation.

Larry

 

[Bill D]

My 1974 house has three bathroom fans that each have a foot or so of flex hose that gets the exhaust out above the glass insulation. It works. The attic has soffit vents and ridge vents, but no forced ventilation.

Larry

And it fills the attic with warm moist air providing the perfect environment for mold and fungus. in winter it turns to ice that melts in the spring as the mold warms up and starts growing again.
Bill D

 

[Milacron]

Update - I figured out a way to get safely on the roof and found the below. No way to take it apart aside from removing the entire cover but looking thru the vent slots it appears the vent pipe simply ascends to half inch or so below the top of the vent sheet metal. In other words, no damper, all looked pristine as new, no dirt, nothing. The vent "works" by simply having a open pipe, protected from rain and birds nests by this $20 cover. So I presume now the issue is a half assed designed system that never really worked from day one.

If you are wondering, the previous owner of this house, since new, was a widow who only used one of the showers (or took baths !), so she probably never noticed a problem. So if you guys agree with my theory then looks like a fan mounted in the manifold is the most practical solution.

https://www.lowes.com/pd/Air-Vent-Black-Aluminum-Slant-Back-Roof-Louver/3017497?cm_mmc=shp-_-c-_-prd-_-bdm-_-ggl-_-LIA_BDM_103_Roofing-Gutters-_-3017497-_-local-_-0-_-0&ds_rl=1286981&gclid=Cj0KCQjwjbyYBhCdARIsAArC6LIEEbLbmR056mdZywuQDtOAWu_91h9rW52t9CHsdPKCJcRq9rm8Zj4aAjmrEALw_wcB&gclsrc=aw.ds

 

[DDoug]

...of at least 10 h.p. .....

 

[blcksmth]

Our house built in 1996 has 3 bathrooms with one fan unit in the attic that is vented to the outside. The fan housing is about one foot square and 8 inches thick with hoses to each bathroom and to the outside vent. Wiring the wall switches in each bathroom required some attention.

Bob
WB8NQW

 

[eKretz]

Sucks not having a damper. In winter that is like a big direct cold air inlet to 5 rooms of your house. I had a failed damper on my dryer vent last winter and noticed it felt extra cold in the basement. The cold air was coming in the vent and using the dryer as a cold air radiator! It was around 0°F the day I took the images. That pipe from the dryer vent was at 4°F and a large part of the front of the dryer was 37°F.

 

[jtaylor]

Try one or two of these: https://www.supplyhouse.com/Panason...-340-CFM-Remote-Mount-In-Line-Ventilation-Fan

 

[Scottl]

Is there room to add an inline damper as well as an inline fan?

https://www.amazon.com/QWORK-Backflow-Preventer-Ventilation-Deflector/dp/B09NNLFYHK/ref=asc_df_B09NNLFYHK?tag=bngsmtphsnus-20&linkCode=df0&hvadid=80608073959558&hvnetw=&hvqmt=e&hvbmt=be&hvdev=c&hvlocint=&hvlocphy=&hvtargid=pla-4584207593408881&psc=1

 

[Dennisrech]

Moved into new townhouse (2010 construction) a few months ago and just now noticing a vent issue due to mold forming on vents. The vents have impressive looking fans, but draw very little air (test with strip of toilet paper right at the vent and paper barely moves). So wondering if the problem is the manifold concept is a bad design or a stuck damper on the roof vent ? (which I would have checked already but due to roof pitch and height I'd be risking my life )

Are you sure that the problem is not at the fan? Does it have a propeller fan or does it have a squirrel cage fan? If squirrel cage, are the blades clean. Sometimes they have a layer of dirt that fills the cup of the blades and no air is pulled through. I would guess that the fan end of the hose is the problem. Can you remove the hose at the fan and check if the fan is actually blowing? Dirty blades or a chunk of insulation in the fan or duct may be the problem. Most fans have a flapper damper at the fan exit. Is it stuck closed? Is the hose actually connected to the fan? Have rats gnawed through the hose?

 

[Superbowl]

All the bathroom fans I have seen have an individual built in damper inches from the motor. No reason for a damper at the roof exit.

 

[Superbowl]

Are you sure the mold is recent. I suspect it is from when it was cold in the attic during winters. What happens is warm moist air is blown into the ducts where it condenses on the cold metal. If the duct runs flat along the ceiling joists then the water stays in the duct. If the duct is tilted up towards the ridge, then the condensed water runs back down and drips onto the fan grill. The damp grill in the warm conditioned bathroom grows black mold because it stays damp for a long time.