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I have a fan in one of the bathrooms of a 1930s house and there's a relatively low ceiling. The fan seems to work ok and it's in pretty decent shape(seems to be from 2013), but I think we need a bit more power as we're getting excessive condensation on the ceiling. If my wife and I shower back to back it looks like our ceiling has a leak. I can't seem to find this model (see below pictures) - ideally I'd like to be able to swap out the motor if possible (seems like the path of least resistance). I am decently handy with electrical work (and rapidly gaining more experience in this old house) and can generally figure things out using the good old scientific method. Am I getting in over my head here or is this worth doing myself? Also would that gap cause any problems? Would it help if I use a different paint on the ceiling? I assume it's a standard flat-white ceiling paint, but not sure.

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    Many times in those older homes the duct is smaller than 4 inch usually 3 inch. Also you should check the vent where it exits the building in make sure the Backflow flap is not stuck closed. – Alaska Man Nov 28 '18 at 17:45
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    The gap should be patched. – Platinum Goose Nov 28 '18 at 18:37
  • "If my wife and I shower back to back it looks like our ceiling has a leak." Does this happen on cold days only? When humid air goes up a cold metal vent pipe, it condenses on the sides of the pipe and drips down. – Steve Wellens Nov 30 '18 at 17:35
  • @SteveWellens New house so I’m not sure yet, but we have steam heat and it was definitely running at the time so there was definitely extra humidity. Not sure how cold the attic is, but the duct would have to travel probably 10 feet before reaching the vent. – Jordan Nov 30 '18 at 17:52
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Most consumer-grade fans are not designed for upgrades. My recommendation is to look for a better fan. The 2 key things to look for are:

  • Airflow - typically measured in CFM - higher is better

  • Sound - measured in decibels or sone - lower is better

  • Are these pretty standard size? Is replacement difficult? I don’t have easy attic access although this is at least near the opening. – Jordan Nov 28 '18 at 15:08
  • No standard size that I know of. Replacement is usually not too difficult for the wiring. The big catch is the ductwork, which is where you may need attic access. – manassehkatz Nov 28 '18 at 15:25
  • I can’t just attach it to the existing ductwork? ... well I do need an external dryer vent installed so maybe I can just use the same contractor I use for that.. – Jordan Nov 28 '18 at 15:29
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    There are standard sizes. But sometimes the duct comes out on a different size or a different shape. What I would recommend, if possible, is to get the installation manual for the old & for a new one that you are considering and see how they compare. – manassehkatz Nov 28 '18 at 15:38
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    @Jordan If the hole is square, you can most likely rotate the new one to have the exhaust hole line up with where the existing duct work is. If the new one is bigger than the existing one, just make the hole bigger and ensure you do so in a way that the exhaust lines up with the duct work. Yes, they're pretty easy to replace, I did one about a year ago. It's messy cutting into plaster & lath (likely in a home from 1930) over your head, but a shop vac will fix that. – FreeMan Nov 28 '18 at 15:52
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I had a problem in 1 of my bathroom vent fans last year. The duct from the fan to the outlet was run horizontally in the cold attic. After a few years the poured insulated settled where the flex duct was laid. The resulting water that condensed in that trap reduced the exhaust air flow. The settling insulation allowed a trap in the duct to form and the extreme cold in the attic allowed the humid air to condense and fill that trap with water. Check the fan's outlet, "blow open" and the outside vent damper to make sure that both are working properly. Lastly, check the fans's blades to make sure that they are clean and not coated with dust. You can sometimes clean them "in place" with a small screw driver and air compressor if they need cleaned.

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