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  1. #1
    Join Date
    Jan 2010
    Posts
    55

    venting bath vents to attic?

    My hvac installer claims it is sometimes better to place the vents for the bath ventilation systems in the attic because strong winds will force outside air into the ducting and house. He claims the flappers on the units is not enough to keep all the air out. I just wondered if this is true or is he wanting out of the extra work. He said he'd do it however we wanted. We have 5 bath vents and a range hood vent which he said he would vent the range hood on the roof for sure. most of the runs are fairly long so I doubt if much air is going to be forced inside.

    Also he said he would normally just install a dryer type vent on the side of the house. I'm a little concerned about having 5 ugly aluminum dryer vents sticking on the house. I asked him if he had an upgraded type of vent but he doesn't

    My attic is vented w/ continuous soffit and ridge vent but in most areas there are baffles installed so the ventilation is not really great like it would be for a fully vented attic space.

    thanks. Any ideas are appreciated.

  2. #2
    Join Date
    Jan 2010
    Posts
    6,263
    Why would you want to send all that water to your attic ?

  3. #3
    Join Date
    Jan 2010
    Posts
    55
    That's what I thought. But he's the professional and has been very good (at least I think) at everything else. Any tips on where to terminate the vents (side wall, soffit or roof) and what type of terminations to use other than his cheap looking dryer vents.

    Another thing he told me is that he never puts a supply vent into a pantry. Especially when they are surrounded by conditioned space. He says the room is small enough that it would overheat in the winter and cook my food. I kind of agreed with him. Again he said he'd install the supply as it would come off a nearby supply and only be 10 minutes to do, he just didn't recommend it.

  4. #4
    Join Date
    Sep 2006
    Location
    Montana
    Posts
    983
    I've seen the cost cutting companies just throw it in the attic or some will run it over to the soffit, but why would you want to put all that humidity into the attic? There are other vent options for side discharge. You could use the same type of plastic dryer vent for bath fans as well. They fit fairly flush to the house and look better than the aluminum vent, that's how I would do it.

  5. #5
    Join Date
    Jan 2010
    Posts
    6,263
    One can't be a pro at everything. I'm no pro at bath venting but common sense tells me that's a bad idea. Water in insulation can really lower your R value.

  6. #6
    Join Date
    Sep 2002
    Location
    Northeast Ohio
    Posts
    4,842
    They need to be vented to the outside, period.
    A good HVAC tech knows how, an educated HVAC tech knows why!

    DEM


  7. #7
    Join Date
    Mar 2007
    Location
    tx
    Posts
    1,088
    did you say five dryer vents??? Other reply hit it on the head. You are putting a lot of moisture into the attic,mold..errosion of other materials that may be near,... not good idea. Where I live it would not pass inspection. And at my house, there may be enough methane get up there to blow the roof off!LOL
    Bad information is worse than no information at all.

    There are three kinds of people in this world. Those who can count and those who can't!

  8. #8
    Join Date
    Jan 2010
    Posts
    6,263

    Talking Methane

    Blow the roof off i like that. LMAO

  9. #9
    Join Date
    Jun 2004
    Location
    4H: Hot, Humid Houston H.O.
    Posts
    3,304
    As a homeowner I have worried about that same question, and pros have all generally told me it is against current code to vent to the attic. The theory is always that the attic may be a lower temperature than the bathroom air dewpoint, and condensation has been known to occur in houses that vent directly to the attic.

    Your HVAC pro's statement about wind is something I have never heard spoken professionally before. Perhaps he is mistaken about that risk. Without knowing any more, I would have the job done according to code rather than his way.

    However... there are two sides to the argument. My house is in South Texas where the outdoor humidity is like 72F dewpoint on a normal summer day. The air indoors, even in the bathroom is nowhere near 72F dewpoint (more like 62F max) and the attic is already filled with 72F dewpoint air. Not to mention the attic is almost always 10F warmer than outdoors. Plus there is an issue of dilution of that bathroom air as it goes from the indoors to the attic, and its temperature changes not instantly but over a few inches from the mouth of the exhaust duct. I have the pre-code method of installation and have looked for any evidence of condensation... none seen. In winter both indoor and outdoor have less humidity and the argument about condensation is plausible, but I have looked for it and not seen it.

    You hear all these qualitative arguments about putting "all that water" into the attic, but I question whether any of these people have ever measured the humidity in the air they speak of. Somewhere out there should be a professional study published which *does* measure the humidity in one or more actual houses, but I have not ever seen such a study. Would like to.

    There is a bigger threat in 4-season climates where it is plausible that indoor dewpoint may be higher than attic ambient temperature. The code may be "one size fits all climates" but it is there to address problems somewhere in the real world. I just don't believe it fits all climates. It may not be urgent to retrofit houses which have pre-code exhausts into the attic. But it certainly would be a superior practice to exhaust to outdoors, an inspector may care enough to ticket you, and when you resell your house it might be an issue you must fix before the sale goes through.

    Regards -- Pstu

  10. #10
    Join Date
    Jan 2010
    Posts
    55
    Yeah, 5 vents but they are bathroom vents, I just meant he uses those cheap aluminum dryer looking vents. But I guess I could change those out later if the ducting was there. I suppose that only 3 of the vents will draw moisture out, the other two will just be for the aforementioned methane gas extraction.. Maybe those two could be into the attic just fine as long as nobody is in there to suffer the consequences.

    I appreciate all the comments. I am leaning towards having him vent them out the upper walls or roof. Although I'd rather not have too many holes cut into the roof.

  11. #11
    Join Date
    Mar 2007
    Location
    tx
    Posts
    1,088
    Ok now I understand about all the dryer vents. But just for the record friend, I was really kidding about all the methane. Those vents are installed for two reasons, to pull moist air out from when you take shower etc... and to pull out objectionable odors and such. But you know this, I just don't know if the methane thing scared ya, I was just joking and i want to make sure you know that.
    Bad information is worse than no information at all.

    There are three kinds of people in this world. Those who can count and those who can't!

  12. #12
    Join Date
    Jan 2010
    Posts
    55
    Yes, although I do know it is highly flamable from childhood experiences, and having a scarry uncle.. I know the concentration is not nearly enough to pose any fire danger.

    So if the only reason for two of my vents is to pull out odors, I suppose those two could be vented straight to the attic to maybe keep out extra outside air and limit the penetrations in my siding??

  13. #13
    Join Date
    Mar 2007
    Location
    tx
    Posts
    1,088
    are you saying that two of the vents are on half baths or something that do not have showers/baths?
    Bad information is worse than no information at all.

    There are three kinds of people in this world. Those who can count and those who can't!

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