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Old 04-15-2013, 03:05 PM   #1
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Bathroom Exhaust Duct


Hi,

I am trying to install an exhaust duct for bathroom fan. The house has a 2' bump-out. I'm using a 4" duct.

My plan is to use solid duct (i.e. non-flexible duct) with a little angle so that if there is any condensation inside the duct, the water will not drip into the bath room, but to outside.

When I scoped out the joist location, I noticed an 1" wire connecting the joist (see attached picture), which makes it hard/impossible to tilt the sold duct in an angle.

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Do you know what these wires are?
Any recommendation on how to solve the problem?

Any input is much appreciated.

Thanks!

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Old 04-15-2013, 03:44 PM   #2
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Bathroom Exhaust Duct


Its bridging. Probably tubular steel with flat flanges. You will find it in every bay, its to keep your joists from rolling under load. Put in a solid piece of dimensional lumber (2 x 12? or finger joined 1 by pine cut to fit) with a hole in the middle for your 4 inch duct

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Last edited by jagans; 04-15-2013 at 03:47 PM.
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Old 04-15-2013, 04:48 PM   #3
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Bathroom Exhaust Duct


Do you think it is OK to run the 4' duct on the side of the cross as it has enough opening and use flexible duct at the ends to the outside terminator and to the bathroom fan? This way I can at least run the solid duct in an angle.

Do you think there will be a lot of condensation happening within the duct?
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Old 04-15-2013, 05:06 PM   #4
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Bathroom Exhaust Duct


Sure. Its not a dryer vent. I would use an inline fan, much quieter. Is it cold in between your joists? If it is, you will get condensation on the inside as moist hot air hits the cold duct. If not, Its not a problem.
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Old 04-16-2013, 03:08 PM   #5
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Bathroom Exhaust Duct


Why isn't that bump-out insulated? Location?

Gary
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Old 04-16-2013, 09:21 PM   #6
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Why isn't that bump-out insulated? Location?

Gary
The bump-out is insulated with fiberglass insulation. I am working to put in the exhaust duct, so I removed it for now. I will put it back when I finish.

The location of the bump-out is below the kitchen at the back of the house. Above the joist's end, there is a double door that leads to a patio stairs. So, I am looking at the bump-out from inside the basement where a full bathroom will be.

I hope my explanation makes sense
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Old 04-18-2013, 06:34 PM   #7
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Bathroom Exhaust Duct


Is there any regulation requirement on the distance between the exhaust fan from the shower?
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Old 04-18-2013, 11:33 PM   #8
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I was going for the climate location eg.Iowa, for the required minimum insulation R-value you should have in the bump-out floor cavities.

Gary
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Old 04-19-2013, 05:17 PM   #9
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I was going for the climate location eg.Iowa, for the required minimum insulation R-value you should have in the bump-out floor cavities.

Gary
Virginia. The builder installed the insulation, so i hope the inspector did inspect it. I will be putting the same insulation back into the bump-out cavity.

Do you think I have to install additional insulation because I'm putting exhaust duct (i.e. opening to the outside?
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Old 04-19-2013, 07:27 PM   #10
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No, just put back what was there, but keep the duct on the warm side of the insulation.
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Old 04-19-2013, 10:20 PM   #11
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The bath fan termination hood/exhaust is required to be 3' from any operable door/window on the outside of the house. Air supply to HVAC, etc, also.

The cross bridging appears to be in line/directly over, the supporting exterior wall plate? If so, (IMHO) I would not replace it with solid wood, or anything- at least one bay as the rest are intact and fastened top/bottom.

Why is the sub-floor discolored: as if by mildew?

Once you cover the new bath ceiling with drywall, you will find the upstairs floors much colder above the cantilevered portion as you cut off any warm air movement with the changes. You may want to think about foamboard under the joists on the outside if room/accessibility, or adding f.b. on the floor sheathing/rim joist area of the bump-out before the new ceiling. Fig.7: http://www.buildingscience.com/docum...n-crawlspaces/

If adding it inside, canned foam/caulk it to the bottom chord of the I-joist and one on the rim; http://www.buildingscience.com/docum...l_seal_rev.pdf
This would stop the whole bump-out from acting as a heat sink and stop infiltrating outside air. Air moves easily through f.g. insulation unless air sealed with something else.

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Old 04-19-2013, 10:43 PM   #12
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Bathroom Exhaust Duct


A few years back I installed an inline fan, but I did not want to put it in the attic where it is very hard to get to if it needs servicing, not to mention it would have been more complicated as far as insulation/vapor barrier etc goes. So I ran some insulated flex from the inlet into ABS pipe going downstairs through the hot water chimney chase (kinda got lucky it was right there) then the fan is in the basement and exits with aluminium ducting through a dryer vent.

Probably a good 20 feet of 4" pipe going through 3 different types of piping. It can still suck a piece of cardboard right up against the inlet, and if I close the bathroom door the hand towels move since air is being sucked out of the heat register through the duct work. Inline fans are quite powerful and can tolerate longer distances. The best thing is it's ultra quiet, even 2ish years after the install. I'd never go back to a traditional fan again. They tend to get noisy and lose performance after only a few years.
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Old 04-19-2013, 11:10 PM   #13
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Thanks for your input Gary!

Quote:
Originally Posted by Gary in WA View Post
The bath fan termination hood/exhaust is required to be 3' from any operable door/window on the outside of the house. Air supply to HVAC, etc, also.
I am planning to use an exhaust fan that has a heater as I am not planning to put an ac/heater air duct into the bathroom, which may complicate my heating/cooling system. Based on my proximity guess, the joist choices are either too close to the shower, or 2 - 3 joists away. I don't think the distance from the bathroom door will be more than 3' away.

Quote:
Originally Posted by Gary in WA View Post
The cross bridging appears to be in line/directly over, the supporting exterior wall plate? If so, (IMHO) I would not replace it with solid wood, or anything- at least one bay as the rest are intact and fastened top/bottom.
After reviewing the size of the cross bridging, I may have enough clearance for 4" duct size. I still can install the duct with a few degree tilted.

Quote:
Originally Posted by Gary in WA View Post
Why is the sub-floor discolored: as if by mildew?
No, the bump-out (2') is over hanging the basement wall. What you see is NOT a sub-floor, but the bottom of the bump-out. There seems to be a white powder coat. My guess is that it comes from f.g. insulation. It has been like that since I bought the house (I think).

Quote:
Originally Posted by Gary in WA View Post
Once you cover the new bath ceiling with drywall, you will find the upstairs floors much colder above the cantilevered portion as you cut off any warm air movement with the changes. You may want to think about foamboard under the joists on the outside if room/accessibility, or adding f.b. on the floor sheathing/rim joist area of the bump-out before the new ceiling. Fig.7: http://www.buildingscience.com/documents/insights/bsi-009-new-light-in-crawlspaces/
I am planning to use suspended ceiling and to put f.g. insulation for noise. I don't know if this would also do the trick in keeping the upstairs floor warm.

Quote:
Originally Posted by Gary in WA View Post
If adding it inside, canned foam/caulk it to the bottom chord of the I-joist and one on the rim; http://www.buildingscience.com/docum...l_seal_rev.pdf
This would stop the whole bump-out from acting as a heat sink and stop infiltrating outside air. Air moves easily through f.g. insulation unless air sealed with something else.
The builder pack a good amount of f.g. insulation within that 2' bump-out.
Here are pictures before I pulled the insulation out and the f.g. insulation after I pulled out.

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Last edited by 325_man; 04-19-2013 at 11:20 PM.
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Old 04-20-2013, 06:47 AM   #14
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Bathroom Exhaust Duct


Insulation almost performs worse than nothing when it's installed improperly. That looked like a pretty poor installation job.

I've had Fantech in-line fans for ages and they're great. Quiet and reliable. The new house has seven of them. Thankfully they're less expensive than they used to be.
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Old 04-20-2013, 11:10 AM   #15
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Bathroom Exhaust Duct


The 3' rule is on the exterior of the house, and it is for dryer ducting only, my error... sorry.

There is a code for overhead electrical being within reach of a shower/tub, but I don't have it in front of me, anyone else?

The white, powdery coating is usually mildew...

Anytime you "pack" insulation (including your scraps) in a cavity, you have air chases to degrade the R-value; http://www.advancedinsulationinc.com...Insulation.pdf

Gary

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