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My home's master bathroom has an oversized step-in shower -- two showerheads, frankly over the top. Bathroom exhaust fan does a fine job preventing moisture build-up in the bathroom during even long showers with both showerheads. BUT, moisture lingers in the shower area. Exhaust fan is well outside the shower. I feel the exhaust fan is drawing in external air from the rest of the living space, and exhausting that air out the exhaust fan, without pulling much air from/through the shower.

As an experiment, I put a box fan at the entrance to the shower. After showering, I turn on the box fan, which amply circulates air from shower into the rest of the space. When I run the box fan for 20+ minutes, the shower area dries out just as well as the rest of the space. But this is unsightly, intrusive, and manual.

I have thought about ways to get make-up air (from elsewhere in the house) into the shower area, so that exhaust fan would pull air from the shower area. Broadly, I'd install some kind of grille in the shower, angled so that water drains down but air can come in. Grille would connect to a duct to some other nearby other part of the house. Don't feel great about this because it feels ad hoc, and access is limited behind the shower area. Also prefer not to cut tile, as I don't have any experience working with tile.

I also thought about ways to try to increase circulation in the shower area. I have excellent access from above (attic) so could install any kind of ceiling-mounted fan. Certainly wouldn't want a full ceiling fan. What about a tiny fan (potentially as small as a USB desk fan), mounted to ceiling or wall, controlled by the same switch that turns on the exhaust fan? I'm confident in my ability to mount and wire such a fan. Feel it would help the problem. Nonetheless, I'm hesitant. One, I feel like a code restriction would prohibit or limit such a fan in or around a shower. More than that, I've never heard of anyone doing any such thing. Why not? I can't be the only person with a dead-end shower area needing improved air circulation.

2003 home in greater Seattle. Terrible sketch follows bathroom layout.

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    Edit: I just noticed in your diagram the shower has no door. Have you tried closing the bathroom door while running exhaust? Aug 23 at 14:30
  • Robert, I have tried that sometimes. Doesn't seem to make much difference. Could you say more about the theory of why this would help? If the entire bathroom were fully and tightly air-sealed, I need makeup air from somewhere. Certainly my house has leaks -- window seals that are not perfect, etc. -- but the bathroom area is pretty airtight I believe.
    – Ben E
    Aug 25 at 6:15
  • I was curious if the issue was specific to the shower area. And to be clear, have you left the door closed and the exhaust running for 20+ minutes after the shower? Or was that only done with the box fan? Does the shower wall have an air gap at the top? Aug 25 at 17:04
  • Issue is specific to the shower area. Rest of the bathroom dries out well and quickly. The shower is walled in but has no door. Just an open threshold to step over. So huge opening -- three feet wide by 8+ feet tall -- between shower and the rest of the bathroom.
    – Ben E
    Aug 26 at 16:04
  • Having a walled-off shower changes the way the air moves. Even adding an exhaust near the shower opening might not work as well as your box fan. Do you have any nearby HVAC registers that could be directed toward the shower? Aug 27 at 17:56
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Another exhaust fan.

If you can easily approach from above, put another exhaust fan on the ceiling inside your shower. All showers in this house have one. You have 2 exhaust fans already in the bathroom so your new fan could share some of the duct with one of them, or you can cut another hole.

It will pull air thru into the shower and out which is ideal. Also when you go to sell the house there will be no ad-hoc looking DIY stuff in evidence. A shower exhaust vent is not weird.

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Looks like you already have two separate exhaust fans. You could try consolidating and adding a vent right above the shower enclosure by installing a powerful enough (i.e., enough CFM) in-line bath fan. You would have 3 ducts feeding into a single fan with one single exhaust duct to the outside. Rigid ducting for greatest efficiency though it may sound louder than flex duct; or maybe use a combination (flex at vents in ceiling to fan, rigid after fan to exhaust port).

There are some companies that will sell the fan as well as a kit for multiple vent ports - the vent grille, the damper to keep out air, wyes for splitting the line.

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  • Thanks for this suggestion. I suppose I could also just install a third exhaust fan -- this one right above the shower. Putting them on separate switches will let me use them in any combination, which is attractive because I'm looking to focus my ventilation, not increase ventilation. Agree that I need to make sure there is sufficient ventilation through the attic -- check airflow from each fan, and size of the duct to the roof penetration.
    – Ben E
    Aug 25 at 6:19
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The exhaust fan for your shower in a bathroom that size should be about 1-2 feet outside the shower. It's just too far away there. I am sure someone theorized that the middle was better but people take more showers than baths and showers produce more steam. The fan is just in the wrong place.

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  • Thanks. That's helpful. Suggests installing a third bathroom exhaust fan, this one squarely above the shower. Also as achao suggested (above).
    – Ben E
    Aug 25 at 6:16
  • Third exhaust seems like overkill. But it would be a way to fix issue. I would just move the fan and patch ceiling.
    – DMoore
    Aug 25 at 15:56

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