Bathroom fan ducts

[joso]

I lived in an apartment for many years and one of the difficulties I faced was lack of proper ventilation in bathroom. As a result, we had constant mildew and mold problems. The landlord painted the bathrooms 4 times. Was I ever glad to move out of that place.

Due to this experience, I decided that my new home (which closed June/07) would have stronger bath fans. The builder's model was 50 cfm in Master ens. & Bedroom 3 ens., and 90 cfm in Main bath.

I hired electricians (since I had no clue about anything involving a house) to remove the builder's model and install the fans I purchased from HD. Master ens. & Main bath 110 cfm - 1.5 sone, Bedroom 3 ens. 90 cfm - 1.0 sone - all made by nutone.

While installing, the electricians encountered a problem. The builder's fans were all connected to 3" insulated sheet metal ducts. The new fans required 4" ducts. So the electricians went to HD and apparently got 4" ducts, but they were flexible aluminum ducts (not insulated).

I saw an old episode of Holmes on Holmes one day where Mike was working on a home with this kind of duct. He took it out & put in ducts similar to the one's my builder originally installed. He gave some reasons for the change including condensation buildup in the ducts - cold attic/warm moist air after shower and you get water build up in ducts.

I am worried about this. Should I get these ducts replaced with the solid metal insulated ducts, or is this ok? Anyone have experience using these ducts connected to their bathroom fan?

[Drthorne]

I would recommend the solid ducts in 4" line, only use that flexible stuff if there's no way of running the rigid stuff. There's just too much air flow resistance on that aluminum corrugated flexible duct

[joso]

I would recommend the solid ducts in 4" line, only use that flexible stuff if there's no way of running the rigid stuff. There's just too much air flow resistance on that aluminum corrugated flexible duct

Thanks Drthorne.

I just spoke with 2 HVAC companies that do duct work.
Both recommended factory insulated flexible duct at this point.
Both stated that solid ducts with insulation would be difficult to put in, more labour intensive, therefore, more money.
The factory insulated flex lines, bit more expensive, but save on installation cost (less labour).

Concerning air flow resistance, the insulated flex lines inner lining stretched out to be as smooth as possible.

Also, they warned me that when insulation is put in around solid ducts, gaps can occur defeating the whole purpose of insulating the ducts.

Any recommendations? Thanks.

[scoop]

Thanks Drthorne.

I just spoke with 2 HVAC companies that do duct work.
Both recommended factory insulated flexible duct at this point.
Both stated that solid ducts with insulation would be difficult to put in, more labour intensive, therefore, more money.
The factory insulated flex lines, bit more expensive, but save on installation cost (less labour).

Concerning air flow resistance, the insulated flex lines inner lining stretched out to be as smooth as possible.

Also, they warned me that when insulation is put in around solid ducts, gaps can occur defeating the whole purpose of insulating the ducts.

Any recommendations? Thanks.

I just added a bathroom fan and picked up a 10 foot 4" flexible insulated duct from Rona. It was plastic, but you shouldnt need metal for a bathroom fan. I think it was about $25.

[phatmanmd]

i have an old house where the bathroom was not previously vented. i installed a bathroom fan this summer and vented it to the outside, thru the roof. i ended up using an aluminum flexible duct, and i bought duct insulation to around it (slides over the duct like a sock - and you connect the duct either either end afterwards). only reason i did this was it was more labor intensive to buy all the parts and joints for rigid ducts, and align them up with the roof vent and screw them all together (while sitting in my dirty 100-year old attic).

for a 90cfm fan and a 4" duct - the main limitation of airflow will be at the outlet (in my case, a covered roof flap that opens a couple inches if the fan's on), NOT the ridged texture of the flexible duct. secondly, if the moist air from a shower is going to condense, i don't think it'll make a difference whether you have a smooth rigid duct or a flex - you'll get droplets regardless!

[Neil]

You didn't mention the length or amount of corners in your ducting. If it's really short with few turns, maybe that offsets the flow reduction caused by the ridges in your flexible vent?

[Neil]

Anyone have a guideline for how strong bathroom vents need to be at a minimum?

My setup is a central fan in the basement that supposedly is 150 cfm, running 3 bathrooms on the main and 2nd floors above.

The HVAC installer says it's working but is just very subtle. I can't notice any air pulling whatsover though. It won't hold a kleexex or even draw a kleenex toward the vent opening. Is there some objective way to prove to him it needs to be fixed or upgraded? Are bathroom vents really supposed to be that subtle?

[joso]

Anyone have a guideline for how strong bathroom vents need to be at a minimum?

My setup is a central fan in the basement that supposedly is 150 cfm, running 3 bathrooms on the main and 2nd floors above.

The HVAC installer says it's working but is just very subtle. I can't notice any air pulling whatsover though. It won't hold a kleexex or even draw a kleenex toward the vent opening. Is there some objective way to prove to him it needs to be fixed or upgraded? Are bathroom vents really supposed to be that subtle?

Hey Neil.

Check out CMHC website on bathroom & kitchen fans.

http://www.cmhc-schl.gc.ca/en/co/maho/yohoyohe/momo/momo_004.cfm

Also check out askthebuilder.com (ventilation - "sizing the exhaust"), this is an American site but I think you'll pick up a few things from here.

http://www.askthebuilder.com/Ventilation.shtml

Central fans would be great, considerably less noise in bathrooms. However, if you're saying the vents can't hold kleenex, I think you'll have problems later on. The condo I rented for about 1.5 years before moving to this new house had a central fan for both ensuite and main bath. The fan was located closer to the ensuite. When I placed kleenex over vent in ensuite, the vent held it. In main bath, the kleenex always fell to floor. You can guess which bathroom had more mildew on bath/shower tile grouts. I say "more" because the fan was not as strong as was required. Therefore, mildew began forming in shower stall. But again, nothing compared to main bath.

Hope this helps.

[rajchakra]

I am also planning for this for my two bath rooms this weeend;After some research,I found out that Panasonic fan is the best in the market and regarding sizing general principle is 1.1x sq ft of the bath room to get cfm of the fan.A little higher is ok too.
Regarding insulated duct,I am also looking for 4" flexible insulated pipe which will go outside roof with proper damper.
I have planned to give bath room stuff to a contractor and ducting to another insulation contractor who will do my attic insulation as well.I shall let you know after they finish jobs hopefully by next week.

[l69norm]

....I am worried about this. Should I get these ducts replaced with the solid metal insulated ducts, or is this ok? Anyone have experience using these ducts connected to their bathroom fan?

Why not just wrap insulation around the the existing flex ducts?
http://www.wrap-on.com/images/photo-pi-bulk.jpg

[WalnutCrunch]

I am also planning for this for my two bath rooms this weeend;After some research,I found out that Panasonic fan is the best in the market and regarding sizing general principle is 1.1x sq ft of the bath room to get cfm of the fan.A little higher is ok too.
Regarding insulated duct,I am also looking for 4" flexible insulated pipe which will go outside roof with proper damper.
I have planned to give bath room stuff to a contractor and ducting to another insulation contractor who will do my attic insulation as well.I shall let you know after they finish jobs hopefully by next week.

I can't say enough good things about Panasonic fans. I know other companies are finally coming out with quiet fans but IMO they're still the best.

You may want to consider rigid ducting if possible. I initially installed my Panasonic with flex ducts. I was disappointed that while it was quiet, it was louder than I had expected. A year later I changed it to rigid ducts and it's noticeably quieter now. So the ducts do make a (small) difference.