[Chonks]

I've gathered on here that soffit discharge of a bathroom exhaust is pretty much no bueno... soffit intake vents need to be far enough away (not sure how far). What do yall think of this? Looks like it basically tries to blow the moist air away from the house. Think this is a good idea? At minimum it's better than just spitting it out thru a hole in the soffit.

Best Soffit Vents | PreVent-It

Best soffit vents to improve airflow in attics and bathrooms. Extend the life of your roof. Prevent moisture concerns that lead to mold and mildew growth.

soffitvent.com

 

[Chris616]

For an installation like shown in your photo I expect that it could be quite effective. The only way to really know would be, after installation, watch where the vapour stream goes on a cold day.

Things that could make it not effective:

• If the existing vent exits the soffit in a location such that the “soffitvent” outlet isn’t actually out past the fascia. That could be fixed with more work to relocate the duct.
• If the prevailing winds push the outlet vapour stream back under the soffit before it can rise because of its buoyancy.
• A weak fan, or poor duct design/layout that causes the moist air to not have much velocity when it exits the device.

More info here:

Best Soffit Vents | PreVent-It

Best soffit vents to improve airflow in attics and bathrooms. Extend the life of your roof. Prevent moisture concerns that lead to mold and mildew growth.

soffitvent.com

 

[Chonks]

For an installation like shown in your photo I expect that it could be quite effective. The only way to really know would be, after installation, watch where the vapour stream goes on a cold day.

Things that could make it not effective:

• If the existing vent exits the soffit in a location such that the “soffitvent” outlet isn’t actually out past the fascia. That could be fixed with more work to relocate the duct.
• If the prevailing winds push the outlet vapour stream back under the soffit before it can rise because of its buoyancy.
• A weak fan, or poor duct design/layout that causes the moist air to not have much velocity when it exits the device.

More info here:

Best Soffit Vents | PreVent-It

Best soffit vents to improve airflow in attics and bathrooms. Extend the life of your roof. Prevent moisture concerns that lead to mold and mildew growth.

soffitvent.com

I ordered one to try it out. Currently my bath exhausts have zero ducting so it'll be an improvement. Rough numbers with a 7"x3" outlet, I get:
50 cfm = 5.7 fps = 3.9 mph
80 cfm = 9.1 fps = 6.2 mph
100 cfm = 11.4 fps = 7.8 mph

That could overcome some decent wind. Will put it up and find a smoke machine to test it. Will report back.

 

[SW Dweller]

bath fans are weak to begin with. Flex pipe of any sort would render this almost worthless.

Metal pipe and a metal elbow and a very short run of pipe might do the trick.

 

[Chonks]

What does framing look like where the wall and ceiling meet? If the duct runs on top of ceiling drywall, will it have to hop over the top plate of the wall? Or will it run smoothly into the eve/soffit area?

 

[Nealtw]

What does framing look like where the wall and ceiling meet? If the duct runs on top of ceiling drywall, will it have to hop over the top plate of the wall? Or will it run smoothly into the eve/soffit area?

I would not do that but most older houses that would be a straight run, in a newer house the rafters might sit on top of a rim joist and you would have to go thru that.

 

[Chonks]

I would not do that but most older houses that would be a straight run, in a newer house the rafters might sit on top of a rim joist and you would have to go thru that.

"I would not do that" - Can you be more specific?

From what I've seen, it looks like my whole roof structure was just set on top of the walls. I'll have to look over the garage to see. Maybe pop off a soffit vent and feel around.

Edit: house built in 1996

 

[Nealtw]

"I would not do that" - Can you be more specific?

From what I've seen, it looks like my whole roof structure was just set on top of the walls. I'll have to look over the garage to see. Maybe pop off a soffit vent and feel around.

It should be like this

in some newer houses they add what is called a raised heel for more insulation.

 

[Chonks]

Little update. The 4" duct is just ever so larger than the gap between the roof deck and wall plate. Going to get a flat/box section or 3" reducer to make it thru that point. Waiting till roofers start/finish in a couple weeks to ensure nothing gets punctured. Will have to pin this thing down so future roof jobs aren't an issue either. It's definitely not a matter of "just running the duct thru." I'm not even attempting to get close to the soffit via attic. Once I'm within ~10, the roofing nails become a hazard while trying to ferret my way closer.

The vent product itself feels nice. Definitely much heavier duty than typical building products. I assume that's because it's made by a company that makes other misc plastic stuff that needs to be tougher (water cans, flower pots, misc vacuum molded plastic stuff).

 

[Chonks]

Well I finally got it in. It’s got about 8’ of 4” semi rigid and a foot or two of 3” so it would fit thru the wall/roof gap. Turning the fan on and putting my face in front of the discharge, I feel a nice breeze from a couple feet away. My Panasonic fan is “smart” and adjusts the fan speed according to “actual” air flow. Probably looks at RPM and current then compares that to a table of corresponding cfm. The fan turns much faster now that it has all that ductwork. I’m happy with it I think.

 

[bestofjess]

@Chonks - What did you add to get the soffit vent to protrude beyond the "lip" of your soffit? I have the same issue and need to add a similar box like you did. Any guidance would be helpful!

 

[Chonks]

@Chonks - What did you add to get the soffit vent to protrude beyond the "lip" of your soffit? I have the same issue and need to add a similar box like you did. Any guidance would be helpful!

The flat panel ~1/4" plywood I had from another job. It's so large cause I went thru an existing soffit vent and had to cover the whole hole up. The "box" is four pieces of 2x4 that I ripped to the correct size and screwed in from the top of the plywood. When doing this, bigger is better. Cut the plywood >6" larger than you need cause you will be glad you had the wiggle room. Also make the box thing bigger than you need. I had to do quite a bit of fiddling to get the duct to lay nicely in the soffit area.

When I did the second bathroom on the other side, I used 4" flexible duct. The choice was to use 3" semi-rigid or 4" flexible to get over the wall. I opted for flexible since the run to the soffit was like 3' and I just didn't want to fool with the semi rigid. Flexible is so much easier to work with in tight spaces.