Another bathroom exhaust vent question

psilva8 · 01-24-2012, 03:40 PM

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.

titanoman · 01-24-2012, 04:06 PM

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).

psilva8 · 01-24-2012, 04:43 PM

Quote:

Originally Posted by titanoman

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.

**Gary in WA** · 01-24-2012, 07:08 PM

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

psilva8 · 01-24-2012, 08:16 PM

Quote:

Originally Posted by GBR in WA

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.

titanoman · 01-24-2012, 08:28 PM

I apologize. I forgot to say stretch out the flex.
Just as efficient, cheaper, and a lot easier. It's just an exhaust fan.

**Gary in WA** · 01-27-2012, 10:51 PM

"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

01-24-2012, 03:40 PM	#1
psilva8 Member Join Date: Jan 2012 Location: Canada Posts: 219	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.

01-24-2012, 04:06 PM	#2
titanoman Disabled wood vet Join Date: Nov 2011 Location: California Posts: 1,646	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).

01-24-2012, 07:08 PM	#4
Gary in WA Moderator Join Date: Mar 2009 Posts: 8,843	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 __________________ 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!

01-24-2012, 08:28 PM	#6
titanoman Disabled wood vet Join Date: Nov 2011 Location: California Posts: 1,646	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.

01-27-2012, 10:51 PM	#7
Gary in WA Moderator Join Date: Mar 2009 Posts: 8,843	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!

Another bathroom exhaust vent question