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Old 01-24-2012, 02:40 PM   #1
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Another bathroom exhaust vent question


I feel bad for making a new thread with the ongoing one still on the front page. However, I have a few questions.

I have a 1.5 storey home with a bathroom on the main floor. I do not have attic access in the house. Don't ask me, it's just the way it was built 70 years ago.

My question is, can I vent the fan directly outside through the sill between the first and second floor. I have the perfect situation where I can install the fan between two joists and parallel right out the sill. If so, how would you guys do this? Hard piping? Proper insulation techniques? Appropriate vent flap?

Thanks for the help.

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Old 01-24-2012, 03:06 PM   #2
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Another bathroom exhaust vent question


Absolutely, with just a plastic flex hose with a dryer-type operable grill (just don't put it right under an operable window if possible).

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Old 01-24-2012, 03:43 PM   #3
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Another bathroom exhaust vent question


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Originally Posted by titanoman View Post
Absolutely, with just a plastic flex hose with a dryer-type operable grill (just don't put it right under an operable window if possible).
It will be fairly close, with about 36" vertical separation.
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Old 01-24-2012, 06:08 PM   #4
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Another bathroom exhaust vent question


I'd use hard smooth-wall metal duct not to catch all the condensation from the moisture, flex has double the area (and turbulence) to gather moisture than smooth. Start with double 45* elbows to get some lift, then straight pipe sloped down to the wall termination hood, screw (3) in each section joint, foil tape each elbow segment as they tend to uncouple easily. Insulate the duct and fan box to help prevent condensation from the outside air flapper leaking. Support as needed, or every 4'. Air-seal the housing/drywall joint. I've seen birds get in the 3 door plastic flappers.....LOL.
Foamboard that rim joist bay if opened for work: http://www.buildingscience.com/docum...l_seal_rev.pdf

Gary
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Clothes taking longer to dry?
Clean the dryer screen in HOT water if using fabric softener sheets.
They leave a residue that impedes air-flow, costing you money.
Clean the ducting in the last six months? 17,000 dryer fires annually!
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Old 01-24-2012, 07:16 PM   #5
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Another bathroom exhaust vent question


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Originally Posted by GBR in WA View Post
I'd use hard smooth-wall metal duct not to catch all the condensation from the moisture, flex has double the area (and turbulence) to gather moisture than smooth. Start with double 45* elbows to get some lift, then straight pipe sloped down to the wall termination hood, screw (3) in each section joint, foil tape each elbow segment as they tend to uncouple easily. Insulate the duct and fan box to help prevent condensation from the outside air flapper leaking. Support as needed, or every 4'. Air-seal the housing/drywall joint. I've seen birds get in the 3 door plastic flappers.....LOL.
Foamboard that rim joist bay if opened for work: http://www.buildingscience.com/docum...l_seal_rev.pdf

Gary
Nice post.

Questions:

1) The floor joists are only 8". It's a small home with a short span. There is no way I will get double 45 in there, however, I will be able to get continuous slope to the rim joist from the fan (only about 7' away)

2) Are you talking about the 4" lock-seam hvac ducting?

3) What do you mean by air seal the housing/drywall joint?

4) For sealing around the duct at the rim joist, would expandable foam work well?

Thanks alot.
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Old 01-24-2012, 07:28 PM   #6
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Another bathroom exhaust vent question


I apologize. I forgot to say stretch out the flex.
Just as efficient, cheaper, and a lot easier. It's just an exhaust fan.
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Old 01-27-2012, 09:51 PM   #7
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Another bathroom exhaust vent question


"1) The floor joists are only 8". It's a small home with a short span. There is no way I will get double 45 in there, however, I will be able to get continuous slope to the rim joist from the fan (only about 7' away)----- That's good.

2) Are you talking about the 4" lock-seam hvac ducting?---- Yes. And insulate it in the flex/insulated/poly.

3) What do you mean by air seal the housing/drywall joint?----- Caulk or low-exp. foam around it at drywall joint.

4) For sealing around the duct at the rim joist, would expandable foam work well?"---- Low-expanding.

The friction loss is great if a long run, go up one size to compensate. Friction = condensation: http://rockwallcontrols.com/Resident...ag=air-ducting
You don't want mold growing in the ducting.

Gary

__________________
Clothes taking longer to dry?
Clean the dryer screen in HOT water if using fabric softener sheets.
They leave a residue that impedes air-flow, costing you money.
Clean the ducting in the last six months? 17,000 dryer fires annually!
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