So here's a scenario: basement bathroom that lost its window when back of house was bumped out. Needs a vent, but no obvious venting opportunity directly out of bathroom (which is basically surrounded on its exterior walls by foundation now). But the dryer vent runs right outside the bathroom--metal duct that runs up from dryer, along ceiling, out of the exterior wall. Opportunity to hook those up? Or run a duct from the fan right next to the dryer duct? Any thoughts/suggestions?

Anonymous wrote:i dont recall how much it was but probably like $300 and it took a couple of hours. he ran duct work along eaves to end of the house. the fan itself is like $50.

did that include running a new line from the breaker?

There is no chimney effect when the fan is off because the damper on the end of the duct is closed. IOW, there is no natural venting, like in a properly insulated and installed attic /roof ventilation system.

The force of the fan is what opens the damper and propels the moisture out, whether it's straight up or to the side. Either works fine. I am the PP who suggested horizontal ventilation, to avoid roof penetrations, but it the roof is significantly closer than an exterior wall that obviously works well too.

You were right to not let your contractor exhaust directly into the attic. That's pretty high on the list of obvious no-nos.

When we gutted and reno'd our bathrooms, my lazy contractor insisted he didn't have to vent to the outside--because my attic has ample cross-ventilation, he swore that sending fan exhaust into the attic was enough.

I insisted that he use a flexible duct to exhaust the fans horizontally to a soffit vent, based on this intuition: venting vertically through the roof (which would have been shorter and easier) would result in heat loss from heat just naturally rising out of the vent, constantly, even when the fan was off. With a horizontal duct, there's not a natural chimney-type flow--the heat rises to flat duct, and stops (or seeps much more slowly), so it's only really sucking out heat when the fan is turned on. Fan might work harder, but it's not a constant heat suck.

Now, this is based on nothing but my intuition. Someone who knows about this tell me: am I right or am I wrong?

I want to install a fan in a bathroom in the middle of a rowhouse (no outside walls). The room has an old, original skylight with a cap at the top that has vents on two sides. (Originally the skylight had a pivoting window that was used for ventilation; now it's covered with a piece of plexiglass that we remove and clean once in a while.)

Instead of venting the fan through the roof, I'm thinking about running the duct up into the attic, then into the shaft of the skylight. (Again, the skylight has openings at the top.) Is this a reasonable idea?

If you get a powerful fan, wouldn't it be ok to vent to roof? Especially if you put in a timer, so it'll run for a bit after you turn off the light.

Anonymous wrote:More efficient because you're not trying to exhaust heavy dense air farther than it needs to go. And, the fewer roof penetrations, the fewer chances for roof leaks.

If there isn't a lot of space between your bathroom and the roof, it is more efficient to blow it directly out of the house through the roof. We noticed a big difference when we moved the ducts from the soffits to the roof. Now we can put a piece of paper to the fan and it will stick to the fan in our bathroom where previously it would float to the floor. The difference in suction is dramatic. Our downstairs bathrooms vent out of the side of the house.

We had an electrician install our fans in the bathrooms and a roofer vented the fans through the roof. - The roofer came first and ensured the existing ducts from the old fans vented properly and then the electrician installed the fans.