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Old 05-17-2017, 12:10 AM  
Snoonyb
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Elbows are "adjustable" from 0 to 90, and using them as close to "0" as you can will reduce their limiting effect upon air flow.

You can accomplish this by the appropriate elongating of the holes in the joists, thereby eliminating elbows.


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Old 05-21-2017, 07:53 AM  
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OK. I think I follow. I have two possible plans right now. One of them has 6 joints with angles of 45 degrees or less. The other plan has 5 angles but one would be a 90 degree.

Neither plan really eliminates 90 degree turns altogether because I basically have to turn 180 degrees to reach the fan box opening. I am just widening the curves. I am not sure if rotating the fan box is feasible but it doesn't seem like something to fiddle around with.

I am leaning toward the first plan with 6 joints of 45 degrees or less and leaving the fan box as is.


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Old 05-21-2017, 09:10 AM  
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What about the possibility of changing the exit to daylight? Is there a straighter option? Just thinking out loud.....
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Old 05-21-2017, 11:08 AM  
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Unfortunately, there isn't a straighter option without ripping up a good bit of subfloor and also cutting out rim board and siding. Also would have to pull up carpet and padding in a bedroom. This would change the exit to the rear of my house (vinyl siding) instead of the side (brick). Then there is no telling what I will encounter as I have learned so far.

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Old 05-21-2017, 11:25 AM  
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What about verticle?
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Old 05-21-2017, 01:14 PM  
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Your plan A will decrease the resistance, IE., back pressure, also, if you have the room, use 2, 45's instead of a 90, for the 90 degree change.
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Old 05-21-2017, 09:29 PM  
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The bathroom is on the first floor which means I'd have to get it up through the 2nd floor and to the attic to run it vertically. There is a wall cavity near where the vent fan is housed but if I am thinking about this correctly, a 4'' pipe will not fit in a wall cavity because the max depth is only 3.5'' because of the 2x4 studs. Sounds like it is some questionable code stuff with that as well. :-P Edit: I guess I could always just leave the pipe completely exposed instead of routing through the walls even though that isn't aesthetically pleasing.

I have been implementing Plan A and reduced 4 of the 90 degree joints into two 45 degree joints by taking a more direct path diagonally. I'm not done yet obviously but near the bath fan box, I plan to make the widest bend I can make within the joist bays to make a 180 degree angle. That will be four 45 degree joints (to make two wide 90 degree joints) and a couple of short straight lengths. This is how I came up with a total of six 45 degree angles Snoonyb. I wish I could make a graphic or something to give a better idea of what I mean because I can't take pictures of the entire length.

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Old 05-26-2017, 10:20 PM  
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I have the whole pipeline complete and just about finished adding insulation except I realize that I have not overlapped the insulation anywhere. I just have coverage on all the pipe except the elbow joints that go through holes in the joists.

Do I need to overlap the insulation? It seems like this would be more of an issue if I was venting through the attic instead of under the 2nd floor of my house but I have no idea how much temperature variance happens there. This room is not over the garage though which I know is a problematic area.

Please tell me I don't need to start this over again. *face palm*
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Old 05-27-2017, 08:15 AM  
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Are you taping the seams?
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Old 05-27-2017, 10:19 AM  
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Yep. I am taping the seams. Practically every seam has sheet metal screws as well as tape.

I am using two types of insulation - fiberglass and self adhesive.






Edit: Kinda hard to capture the whole run especially since some of it is hidden by subfloor but a couple more shots. I have to go back and make sure that seam in the first picture has tape.

A snake through joist


At fan box



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