Bath Fan Through Wall without air leak
Last Post 24 Jan 2013 08:57 AM by propaneBeGone. 18 Replies.
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propaneBeGoneUser is Offline
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18 Nov 2012 08:56 PM
I'm looking for a Through the Wall bath fan that, when not in use, seals out the outside air.  I have seen Panasonic and broan models on line but don't know what really works well.  I read a few comments that the Panasonic units with backdraft dampers do leak some air.  I am concerned about cold new england temps.  Have you found a through the wall bath fan that seals well when off?  Size would be 70 or 80 CFM.  thanks for any ideas
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18 Nov 2012 09:58 PM
You are fighting a no-win battle. Any vent fan that punches a hole into your wall is a source of energy loss/leaks. Even with a damper door, it helps, but all it does is stop some air, it basically have an R-Value of R1. Most damper doors are metal anyways, so you end up with a thermal bridge of the outside air.

Bathroom vent fans are a necessary evil. They do make bathroom vent fans that are HRV units but they run around $300+ and are much larger than a typical vent fan and you will need a 4" or 6" hole in your wall.


propaneBeGoneUser is Offline
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19 Nov 2012 07:20 AM
LBear, thanks for your reply, what would be an example of one of these ERVs?
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19 Nov 2012 09:00 AM
Panasonic FV-04VE1
propaneBeGoneUser is Offline
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19 Nov 2012 09:16 PM
OK, that is very interesting, I didn't know there was an all in one unit like that. Is it usable in a bathroom though. It would be fine to run all the time at low flow but you would need it to also be able to put into shower exhaust mode when needed. Would this work, or a similar unit?
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20 Nov 2012 07:49 AM
No, you wouldn't install it in a bathroom. For that, you'd want a regular exhaust fan to remove the humidity. When it is cold out, this unit, in effect, functions as a regular exhaust fan, to avoid freezing up, but that means you lose the energy recovery. The farther North you go, the less a unit like this makes sense.

Fan penetrations are just a necessary evil.   Make sure they get sealed and the damper works.
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20 Nov 2012 08:09 PM
Another point that is often overlooked. Taking a bath vs. taking a shower, the latter produces much more humidity into the air than the bath. Building off of that point, in open designed bathrooms, the problems of high humidity levels in the bathroom are very low. In my home, I NEVER have to run any vent fans, even during winter because the master bath is completely open (no doors) to the master bedroom. Even after a shower the humidity levels might rise 2%.

Holes in the wall and roof are never a good thing from an energy standpoint. The less, the better.
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25 Nov 2012 07:53 AM
In my case I know I have to do a good exhaust from the shower/bath and I have limited options. It is a post and beam house and there is no sheetrock overhead, just the exposed wood from the 2nd floor. By far the easiest option would be through the outside wall at the back end of the shower, up at 6' or higher. I am wondering if any particular fan has a good sealing, maybe motor driven, damper to close off when not in use. Higher cost for the fan unit is OK vs other more expensive installation options.
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25 Nov 2012 10:43 AM
If you have a through-the-wall fan with a 4" diameter outlet, you could just put a clothes dryer vent on the outside that seals well such as the following:

http://www.amazon.com/HEARTLAND-21000-Dryer-Vent-Closure/dp/B00009W3I4/ref=pd_cp_hi_0
propaneBeGoneUser is Offline
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27 Nov 2012 07:15 AM
that looks like it closes pretty well, good idea!
Eric AndersonUser is Offline
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29 Nov 2012 08:37 PM
That is what I use, a Panasonic bath fan with a Hartland dryer vent. I did have a problem with condensation in the bottom of the hartland vent. In my application there is a 16 ft run from the Panasonic fan to the outside wall exit. I used pvc irigation pipe for the duct run so it would be sealed and gave it 1/4"/ft slope towards the outside wall. It did collect moisture in the bottom of the heartland vent. I could actually hear it bubbling away when the fan was on. I solved it by drilling a 3/16” drain hole in the bottom of the heartland vent. I figure that does not represent enough of an air leak to matter. Interestingly enough I have not had condensation problems with the one attached to my dryer, so that one does not have a hole.
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LbearUser is Offline
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11 Jan 2013 03:33 AM
I've found this unit that ties into a HRV and uses a damper door when it's not in use:

Aldes Vent Zone


YouTube Video

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12 Jan 2013 10:55 AM
thanks, I like the idea of the HRV with increased fan speed.  In fact I saw something similar with other hrvs, fantech I think, anyway there was a kit you could add to an hrv that was and additional inline fan and some controls.  When you hit the switch in the bathroom, it would turn on this inline booster fan for 20 - 30 mins, clearing the bathroom of steam.

However, this system with close off dampers for the other rooms might be more complete.  I'll try to figure that out.  The HRV function would be a plus in my fairly tight house.
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12 Jan 2013 02:11 PM
To be clear, both HRVs and ERVs will freeze up. In the former, cold fresh air condenses moisture from the exhaust air and freezes it. Some HRVs defrost by cyclling room air through the exchanger. Others use an electric element to preheat fresh air. Using either approach in a bath, you'd need extra care to make sure HRV condensate doesn't go where it shouldn't.

ERVs do not freeze in the conventional way because they don't produce condensate. That said, they can damaged by frost. http://www.achrnews.com/articles/should-ervs-be-installed-in-northern climates They can generally hand much colder air than HRVs. http://www.airxchange.com/Collateral/Documents/English-US/Frost%20Control%20Strategies%20for%20Airxchange%20Wheels.pdf I have to believe ERVs can be preheated as well, although I can't point you to an example.

I went with an ERV in northern Zone 3, where extreme cold is rare.
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13 Jan 2013 10:34 PM
The Aldes Vent Zone seems like the best approach. You can have all the bathroom vent fans controlled and running into the HRV. Instead of multiple roof protrusions for bathroom vents, you can have just one side wall protrusion from the HRV.

They make a HRV that has 2 cores, so it has 90% efficiency vs. the 1 core unit which is around 70% efficiency.

Some models use recirculation to defrost the unit, while others use a damper door which brings in room air to defrost. The issue with recirculation to defrost is wouldn't the "stinky" bathroom air get vented right back to the inside?

I calculated I need 200cfm for a 3,400 sqft home. I wonder if it's more efficient to buy an "oversized" unit, instead of maxing out at a unit that has 200cfm max. Maybe a unit that does 270cfm, so it doesn't have to run on HIGH like a 200cfm unit would.


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17 Jan 2013 12:14 PM
Well, no. In either case, the intake stream is switched to house air while the exhaust air stream, stinky or otherwise, continues to be vented to the outside. With a fifth port and a fatter ducting budget, you could pick up defrost air from any point in the house. Recognize that heat exchange is lost during the defrost cycle, and that dehumidification could get out of hand in a heavily populated house. Both factors would matter in the far north. I'm guessing that's why the Panasonic bath units are ERVs although, in the summer in humid climates, the unit could ADD humidity to the house following a steamy shower.
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19 Jan 2013 10:22 AM
I do like the Aldes concept of opening the motorized damper in the bathroom needing ventilation by a timer. Otherwise, damper stays at the minimum position, allowing low level continous ventilation. See figure 2 in this link and hit the light switch to put into high vent mode. http://www.iaqsource.com/article.php/?id=86

So, that could be the vents in bath, maybe kitchen too. I have been looking at a combination HRV / Air Handler to provide ventilation and some heated air when cold outside, radiant floor heat is OK until very cold outside temps. http://lifebreath.com/category.php?category_id=6

Finally, they offer a booster fan that would be started by a switch in each bathroom. http://www.lifebreath.com/downloads/234/69-BES_0910.pdf

If you add together the motorized Aldes dampers along with this booster fan system you can direct the extra exhaust from only the bathroom that needs it, mostly.

So this bath exhaust, on top of normal continous low cfm hrv fresh air, as well as suplemental heat...this might be the IAQ/BATH VENT/SUP HEAT system I need.
There is some sort of defrost cycle on the HRV but I'm not clear what it is so far, have to look into that

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23 Jan 2013 11:23 PM
Posted By propaneBeGone on 19 Jan 2013 10:22 AM
I do like the Aldes concept of opening the motorized damper in the bathroom needing ventilation by a timer.

There is some sort of defrost cycle on the HRV but I'm not clear what it is so far, have to look into that


Let us know if you go with the Aldes setup. I believe the defrost is simply a door opening on the HRV and letting in interior conditioned air. So of course the HRV needs to be in a conditioned space, but I think that goes without saying.
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24 Jan 2013 08:57 AM
thanks, I'll try to flesh it out a bit more
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