Author Topic: Move bathroom vent duct to actually vent outside  (Read 1029 times)

cosine88

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Move bathroom vent duct to actually vent outside
« on: November 09, 2021, 07:36:49 PM »
Two weeks ago, I closed on my second property. I live in it now, and the first one is rented.

One item that came up in the inspection was the bathroom vent in the attic. There's a fan, and a plastic tube for a vent, but the tube just opens up into the attic.

There's a gable vent nearby, so the attic has a good vent, but the tube needs to actually be directed to the vent. Image attached.

Any suggestions on how to connect the two?
1. Get a longer tube?
2. Can I just somehow connect the tube to the gable vent with clips, zip ties, whatever? Is that sufficient?

Honestly not afraid to hire someone, but not sure what sort of contractor to ask. Entering the attic is a bit of a pain and I have more fun things to go do with my spare time.

Paper Chaser

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Re: Move bathroom vent duct to actually vent outside
« Reply #1 on: November 10, 2021, 02:31:01 AM »
The flexible plastic tube is just a standard dryer vent. Honestly, the plastic ones suck and I'm not sure if you can even buy one anymore. They're all metal foil or semi flexible metal now. They come in a few different lengths (8ft is pretty common) and are held together with simple clamps.
If that were my home, I'd throw the plastic vent away and replace it with a metal one of the appropriate length. It shouldn't cost more than $20 or so to DIY and can be done with very simple tools, or perhaps no tools at all depending on the types of clamps used.
The foil style will be easier to work with, but not as robust and will require some sort of support (zip ties or duct specific strapping) to attach it to your framing. The semi flexible metal type of vent is sturdier and might not need as much support, but can be harder to work with. Pick your poison.


nereo

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Re: Move bathroom vent duct to actually vent outside
« Reply #2 on: November 10, 2021, 04:48:17 AM »
+1 to just replacing the plastic vent with metal.  Over time (generally just a couple of years) those plastic tubes all become brittle, crack, and then continue to leak moisture-laden air into your attic while you *think* it’s being vented to the outside.

As for attaching to or venting into the gable vent - I wouldn’t even  bother. 
The proper way is to simply cut a hole in the sheathing along the gable end of your roof, cut around the exterior cladding, and then attach a vent cap (available at any home improvement store) and then caulk around the penetration.  If you have the basic tools necessary (below) it shouldn’t take more than 1 hour to do this - half that if you are handy.

A hole saw is the preferred method for cutting a vent, though many don’t have a hole saw that big.  Instead you can use a jig saw by tracing a circle of the diameter of the vent cap and folllowing the line.  THe hole doesn’t have to be perfect as the cap will allow for you to be “off” by about 1/2” in any one place, and caulk can hide/fix a multitude of sins.

JoePublic3.14

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Re: Move bathroom vent duct to actually vent outside
« Reply #3 on: November 10, 2021, 05:02:02 AM »
+1 to just replacing the plastic vent with metal.  Over time (generally just a couple of years) those plastic tubes all become brittle, crack, and then continue to leak moisture-laden air into your attic while you *think* it’s being vented to the outside.

As for attaching to or venting into the gable vent - I wouldn’t even  bother. 
The proper way is to simply cut a hole in the sheathing along the gable end of your roof, cut around the exterior cladding, and then attach a vent cap (available at any home improvement store) and then caulk around the penetration.  If you have the basic tools necessary (below) it shouldn’t take more than 1 hour to do this - half that if you are handy.

A hole saw is the preferred method for cutting a vent, though many don’t have a hole saw that big.  Instead you can use a jig saw by tracing a circle of the diameter of the vent cap and folllowing the line.  THe hole doesn’t have to be perfect as the cap will allow for you to be “off” by about 1/2” in any one place, and caulk can hide/fix a multitude of sins.

Might be able to rent a large enough hole saw from the same hardware store you get the components. I haven’t look recently at the full lineup of loaners in a while.

OP, good luck! Good to get this fixed.

sonofsven

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Re: Move bathroom vent duct to actually vent outside
« Reply #4 on: November 10, 2021, 05:59:48 AM »
HVAC contractors generally do the venting work in this situation, although in this particular situation it appears to have been done by someone who doesn't know what they're doing.
The "proper way" would be to run it straight up and out the roof in solid 3 or 4" line with very little flex duct.
I wouldn't cut a hole in the siding if you're just going to run it horizontal all the way to the gable vent wall. I wouldn't run it that way but most would and would just attach it to the gable vent and hope for the best. Most likely it would be "fine".

lthenderson

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Re: Move bathroom vent duct to actually vent outside
« Reply #5 on: November 10, 2021, 07:51:13 AM »
As for attaching to or venting into the gable vent - I wouldn’t even  bother. 
The proper way is to simply cut a hole in the sheathing along the gable end of your roof, cut around the exterior cladding, and then attach a vent cap (available at any home improvement store) and then caulk around the penetration.  If you have the basic tools necessary (below) it shouldn’t take more than 1 hour to do this - half that if you are handy.

+1 for doing it this way. If you simply but the tube up to the back of the louvred vent, depending on the pressures in your house, it can be sucked right back inside. By putting in a vent made specifically for this situation, you can also prevent backflow of cold winter air down into your bathroom when the vent fan is not on.

I have seen dozens of houses that vent into the attic and dump the air with no apparent ill effects. It probably depends on location but here in the Midwest, I wouldn't be real concerned about mold, especially if you have adequate ventilation already. I'm not saying I wouldn't make the fix when it was convenient to do so, but I certainly wouldn't be in a rush to fix it.

tygertygertyger

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Re: Move bathroom vent duct to actually vent outside
« Reply #6 on: November 10, 2021, 09:46:58 AM »
Posting mostly to follow, as we need to do this ourselves very soon. Our (yeah, midwestern) house has a small attic and there was plenty of mold up there. The sellers had lived there for 50 years and wanted to see the inspection report as they didn't believe it. Ah well. It's our charmer now.

NaN

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Re: Move bathroom vent duct to actually vent outside
« Reply #7 on: November 10, 2021, 08:01:56 PM »
I am pretty sure the code is 4" rigid wall metal tubing (not flexible) for dryer venting. You can use flexible tubing up to a certain length from the dryer to this run (usually where the main dryer vent is on the wall). The run in the wall, attic, has to be 35 feet or less from that port to exit (obviously outside), and every sharp 90 degree turn knocks off 10ft.

Paper Chaser

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Re: Move bathroom vent duct to actually vent outside
« Reply #8 on: November 11, 2021, 02:42:29 AM »
I am pretty sure the code is 4" rigid wall metal tubing (not flexible) for dryer venting. You can use flexible tubing up to a certain length from the dryer to this run (usually where the main dryer vent is on the wall). The run in the wall, attic, has to be 35 feet or less from that port to exit (obviously outside), and every sharp 90 degree turn knocks off 10ft.

Dryers may have different rules though because they're venting heat and lint which can be a fire hazard. A simple bathroom fan doesn't really generate heat, and shouldn't be venting any fire hazards. You're just trying to get air inside the bathroom out of the bathroom.

NaN

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Re: Move bathroom vent duct to actually vent outside
« Reply #9 on: November 11, 2021, 05:58:59 AM »
I am pretty sure the code is 4" rigid wall metal tubing (not flexible) for dryer venting. You can use flexible tubing up to a certain length from the dryer to this run (usually where the main dryer vent is on the wall). The run in the wall, attic, has to be 35 feet or less from that port to exit (obviously outside), and every sharp 90 degree turn knocks off 10ft.

Dryers may have different rules though because they're venting heat and lint which can be a fire hazard. A simple bathroom fan doesn't really generate heat, and shouldn't be venting any fire hazards. You're just trying to get air inside the bathroom out of the bathroom.

Yes, I thought this was a dryer vent. I think there is a code for bathroom vents but just on the length of a flexible 4" duct, basically when the flow dragged down the volume that moves is less CFM. I think the limit is like 8 ft, but yeah there is no danger other than your fan working the same amount to move less air (maybe harder if it is restricted, which could burn out the fan early).

Woodshark

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Re: Move bathroom vent duct to actually vent outside
« Reply #10 on: November 11, 2021, 03:56:07 PM »
Like others have said, venting a bath fan into the attic in not ideal, but it was pretty common in the past, and not the end of the world.  If this is in a full bath where showers are taken daily it can be a concern as you don't want to dump hot humid air into a cold attic and have it condense back to water. Here is what I would do.

If it's a 1/2 bath or one that's hardly ever used, I would do nothing. OK, I might replace or extend the output hose over to the gable vent if it worried me. If and when I got around to it.

If it's a full bath that sees a lot of hot showers, then yes, I would cut a hole and install a proper vent. Then connect the output of the fan to the vent with a combo of flexible and ridgid vent pipe.

nereo

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Re: Move bathroom vent duct to actually vent outside
« Reply #11 on: November 11, 2021, 07:08:07 PM »
Like others have said, venting a bath fan into the attic in not ideal, but it was pretty common in the past, and not the end of the world.  If this is in a full bath where showers are taken daily it can be a concern as you don't want to dump hot humid air into a cold attic and have it condense back to water. Here is what I would do.

If it's a 1/2 bath or one that's hardly ever used, I would do nothing. OK, I might replace or extend the output hose over to the gable vent if it worried me. If and when I got around to it.

If it's a full bath that sees a lot of hot showers, then yes, I would cut a hole and install a proper vent. Then connect the output of the fan to the vent with a combo of flexible and ridgid vent pipe.
But why?  You’re talking $50 worth of materials and an hour or two of time. The benefit is not dumping moisture into your attic, which leads to all sorts of problems with mold, ice buildup and potentially wood rot.

Clearly it’s not a ‘hair-on-fire’ emergency, but it should be fixed, is cheap to fix, and isn’t hard to fix… so why not do it?

Sibley

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Re: Move bathroom vent duct to actually vent outside
« Reply #12 on: November 13, 2021, 09:45:51 PM »
Two houses....

My house didn't have any sort of bathroom fan. I had one put in when the house was rewired, but it vented to the attic until I had the roof replaced a few years later, it now vents to the outside as it should. I just didn't use the fan so it limited the issues.

Parent's house the fan vented to the attic. Attic had moisture issues, nothing too serious, but they didn't think to address an obvious source of the moisture, ie the fan. I had the fan replaced, and when they did it they also put a new duct in and ran it out an existing roof vent. It's not ideal, but I didn't want to mess up the roof and there wasn't room to get it out the soffit.

If you can easily vent the fan outside, do it. If it's not so easy, then keep it on the list for when something makes it easy. Like a new roof. Don't ignore it though. And if you have problems in the attic because of the moisture, then get it rerouted even if it isn't easy.