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Bath exhaust fan in cathedral ceiling: problem

14 years ago

Our second story bathroom fan exhausts (via the usual flexible tubing) downward between two roof rafters and terminates in the cavity above the roof soffit. The tubing undoubtedly compresses the insulation and carries warm air which causes a loss of heat which inevitably leads to roof icing during our cold New Hampshire winters. You can easily see the limits of the two rafters caused by melting from the heatloss. As a result an ice dam forms at the dripedge and icicles hang from there. Even when the fan is not running I'm sure the tube continues to act as an avenue for warm inside air to excape.

Are there any bathroom fans designed to exhaust directly upward through the roof? One which is energy efficient and that closes off effectivly so house heat just doesn't go up a "chimney"? Can a bath be successfully dehumidified without an exahaust fan, say, with a small dehumidifying unit?

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Comments (4)

pepperidge_farm
14 years ago
Hmmm, that's interesting. We have a fan unit in the attic that vents 2 bathrooms that are side by side. From the unit, the vent duct goes straight up to the roof.

You could certainly insulate the duct work, I am pretty sure we did that mostly for noise (we used rigid ducts and you hear the turbulence, not the fan). We have a cathedral type ceiling in both bathrooms, and we mounted the vent on the vertical wall above the shower head, routed to the motor, then as above (does that make sense to you?). This does not eliminate the heat loss into the duct, but as it is on a vertical wall, rather than the ceiling, maybe it is less like a "chimney", although I am sure we loose heat there too.

This routing avoids running what sounds like a "heat conduit" between the roof and ceiling.

But now I think I will go outside in the morning and look at our roof after over a foot of snow...
microxl
Original Author
14 years ago
Thanks for your reply. It is somewhat heartening to know there may be a ceiling exhaust option.

Our bath fan IS in the bathroom ceiling and there really is no "duct work" at all. It is simply mounted into a framed out area between two joists. The spiral, flexible tubing connects right to the fan housing and this tubing is squished between the sheetrock sloping ceiling and the bat of insulation all the way down to the soffit...a distance of at least 5'. Since it compacts the insulation this tends to decrease the insulation R value.

I was wondering how a vertical exhaust fan through the roof would deal with a thick layer of snow above. We are in NH and have had several storms already. I e-mailed on on-line bath fan dealer to see what they have to offer but no answer yet.
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I live somewhere that ceiling fans are seldom used so I don't know if this would work..but I put a Fantech bathroom fan in my new bath that would suck the fuzz off a peach. It is a very strong motor hidden in the attic space (so it is virtually silent) and it has two fan outlets connected by ductwork, one in the shower and one over the tub. It is a very small grill around a halogen can light (small, maybe 2"? light). It is not noticeable as a fan and if I turn it on, I can feel air being sucked under the bathroom door, a LOT of air. I don't know if air circulation by sucking instead of blowing would work for your purposes, but it would definitely move the hot air off the ceiling. The light and fan operate independently. This is my model and I see they have an add-on so you can have 3 outlets. I chose the halogen because it could be dimmed and was a smaller bulb I think. The premium is rated for a higher cfm. Maybe you could talk to the company and see if they have experience with this kind of application. It is SOOO quiet! Here is a link that might be useful: Fantech
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there are two separate issues that need to each be addressed entirely on their own. in all of this, remember that your fan duct is a chimney and reacts accordingly. you usually have warm air flow and waste even when not "using" it. if you have condensation and it's all in cold weather, insulate the thing. Not with that trendy gimmicky thin plastic junk but with a whole lot of plain old fiberglass. a lot of it. reseal any seams first, perhaps with brush on goop and fiberglass mesh. the water damage is a separate deal and I would not be any way qualified to suggest anything concrete without eyes-on. both issues do seem to be from poor installs. the s-trap is funny, though.
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Fortunately the fan is pretty close to the wall (8' run maximum?). Wall vent is possible although we are a little concerned what it would look like (unexpected to see a wall vent?) Wall is also a concern as the ceiling is cathedral and the steam, etc. is going to want to naturally travel up (away from vent). It would be alcove shower (3x6') with fan outside of the alcove (if ceiling mounted). Alcove does not abut outside wall. I'm not sure about ducting bending the 90 degrees as the duct would puncture the end of roof framing and the top of wall framing (the horizontal pieces). The exterior wall is shorter than average 77" and I am suspecting part of the reason a soffit vent may no longer be allowed for us is the space is very tight, if that makes sense. Duct looks to be around 4" diameter and wall top and end of roof frame is 2x4 (not 6", 40+ year old house). i agree side venting is preferable to going out the roof and having to deal with snow and ice.
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pepperidge_farm
14 years ago
OK, so I didn't make it into the backyard to look up at the roof today- left for work in the dark, home after work in the dark.... that's changing soon, right??

We have been using it since the last storm (meaning we have showered since then!!), and there is about a foot of snow, even the skylights are still covered (gee that glass is well insulated!). The bathroom cleared out completely this morning when I took my typical steamy shower, so...

We are working on the adjacent bath tomorrow, so I will update you. I know I looked at a Panasonic unit, but hubby went and bought something else before we consulted, but it was essentially the same.

Here is a link that might be useful: Panasonic In-line vents
pepperidge_farm
14 years ago
Well, what we have on the roof is a spring loaded damper. It sort of upsidedown U shaped. I can imagine that it could get blocked with lots of snow, although that has not happened here to date, but NW Jersey is not quite the same as NH- you get lots more snow. Hubby and I were contemplating this today, but it has functioned well in the face of about 15" of snow.

Soooo....

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