venting bath vents to attic?

[dforster2]

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.

[VTP99]

Why would you want to send all that water to your attic ?

[big sky hvac]

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.

[dforster2]

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.

[VTP99]

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.

[surenuff]

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

[pstu]

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

[dforster2]

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.

[surenuff]

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.

[dforster2]

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??

[Shophound]

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

Pstu, while your summertime scenario concerning injection of moisture into an attic that is likely wetter than the house holds merit, your area is also not immune to wintertime conditions cold enough for a hot shower and bath fan exhausting into the attic to load it up with moisture sufficient for condensation.

Also bear in mind that a bathroom concentrates moisture when a hot shower is in operation. Few bath fans I've seen, even while running, keep the air sufficiently turned over to prevent the bath mirror from fogging. For hot showers and modestly sized bathrooms, the turnover rate of air to keep mirrors clear and the moisture level comparable to the house would likely be objectionably drafty for a person using the shower.

A cold attic in winter does not naturally ventilate at a high rate, due to reduced heat energy to encourage ventilation. Cloudy days aggravate this, as there is little heat transfer into the attic from the roof deck that could accelerate ventilation rates. Additionally, the air is cold...it can't hold a lot of moisture. Surfaces are also cold, so air that can't hold a lot of moisture can run up to saturation more quickly than warmer air.

It's just not a good idea, aside from code requirements, to ventilate a bathroom into an attic.

[pstu]

Pstu, while your summertime scenario concerning injection of moisture into an attic that is likely wetter than the house holds merit, your area is also not immune to wintertime conditions cold enough for a hot shower and bath fan exhausting into the attic to load it up with moisture sufficient for condensation.

Also bear in mind that a bathroom concentrates moisture when a hot shower is in operation. Few bath fans I've seen, even while running, keep the air sufficiently turned over to prevent the bath mirror from fogging. For hot showers and modestly sized bathrooms, the turnover rate of air to keep mirrors clear and the moisture level comparable to the house would likely be objectionably drafty for a person using the shower.

A cold attic in winter does not naturally ventilate at a high rate, due to reduced heat energy to encourage ventilation. Cloudy days aggravate this, as there is little heat transfer into the attic from the roof deck that could accelerate ventilation rates. Additionally, the air is cold...it can't hold a lot of moisture. Surfaces are also cold, so air that can't hold a lot of moisture can run up to saturation more quickly than warmer air.

It's just not a good idea, aside from code requirements, to ventilate a bathroom into an attic.

Good points. Your mention of the bathroom mirror fogging gives me some important info I have not thought about in a long time. Knowing the mirror fogs tells you the dewpoint, I've seen lots of them fog but not in our own master bath ever, so I more or less forgot about that. In our previous house running the fan would prevent fogging but that fan was high capacity. I'll keep that in mind.

Best wishes -- Pstu

[hearthman]

2009 IRC M1507.2 Recirculation of air. Exhaust air from bathrooms and toilet rooms shall not be recirculated within a residence or to another dwelling unit and shall be exhausted directly to the outdoors. Exhaust air from bathrooms and toilet rooms shall not discharge into an attic, crawl space or other areas inside the building.


I have to say what disturbs me is how often on this site people speak of code issues as if they are optional. Folks, codes are LAWS. Regardless if enforced by your municipal inspector, you are still required to abide by the full code. Even in areas where there is no model building code voted into law, the courts will look to available standards as a generic measure of a Standard of Care. This means other industry standards such as ASHRAE, ACCA, UL, ASTM, ANSI may all still apply to your work regardless if in the local law books or not.

On the practical side, I get into attics often and in most cases where I find bathroom *fart* fans discharging directly into the attic, the insulation and drywall around the fan are moist with either frank mold or rot. Also, those backdraft dampers leak like a sieve. When they are not ducted to the outdoors, particulates in the attic can recirculate back into the home when someone opens a door or turns on an exhaust fan elsewhere.

The code also requires such fan fixtures be sealed to the ceiling. The leakage through the fan at standby is also addressed in the code. If the gravity backdraft damper is ineffective, a fan may need to be replaced anyway. The codes are tightening all the time and I'm sure these fans will be drawn up into the movement as 'can' ceiling lights have. These lights, for ex. must be insulation contact air tight (ICAT) rated, leak no more than 2.0 CFM at 75 Pa and sealed to the sealing.

HTH,
Hearthman

[heaterman]

They need to be vented to the outside, period.

[VTP99]

Blow the roof off i like that. LMAO

[im4snow2000]

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.

Bad idea putting it into attic. For what its worth, residential building codes today do not allow bath vents to terminate in attic, they HAVE to go outdoors......for a reason.

[Logan_L]

I'm curious, has any one seen bath vents conected to an air exchanger? This is the standard practice for the area I'm in.

I assume the reasoning for this is to help reduce heat loss and aid in the prevention of a negative pressure dwelling.

we instiall the standard primary control for dehumidification as well as timer switches in the bathrooms.

[stebs]

I'm curious, has any one seen bath vents conected to an air exchanger? This is the standard practice for the area I'm in.

I assume the reasoning for this is to help reduce heat loss and aid in the prevention of a negative pressure dwelling.

we instiall the standard primary control for dehumidification as well as timer switches in the bathrooms.

I was going to suggest an ERV or HRV connected in a source point configuration. The unit would pull all its house air from the bathrooms and exhaust it to the outside. the fresh air coming in would go through the HVAC system. This way you would not have a fan in each bathroom, and you would only have 2 penetrations going to the outside.

[gailquilter]

Bad idea putting it into attic. For what its worth, residential building codes today do not allow bath vents to terminate in attic, they HAVE to go outdoors......for a reason.

My building inspector required proof the vent went outside, the contractor never gave him proof. Thank goodness, because much later I found out it was
1. an unlicensed electrician,
2. did not have the required 20 amp dedicated circuit for the unwanted heater,
3. and not caulked.
Still don't know if they connected it to the duct which goes outside.

Luckly, I kicked them off the job and never turned on the heater which I didn't and still don't want.

Of course I bought a new fan without the heater and it will replace the one they put in. Have to get the settlement first.

[REP]

I think we all agree that all vents should termminate outside,not in the attic or spare room.
I can understand the concern with looks and with cheap anti backdraft dampers,but there are some very attractive termminationn caps availiable.If you can't find them locally then there is always "google"
You may however need to paint the caps to compliment the roof color or the siding color.
Sometimes doing something right is a pain,but when you're done you will breathe easier every time you look at them.