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I have this model range fan from NuTone.

Condensation from steam (say when boiling water) forms on the underside of the unit and retaining bar that holds motor that drips back down onto the range. It's nasty and I have to wipe it down before it gets into the food (which is pretty much the entire time).

The fan is ducted outside through a long (> 20') flex pipe like this: flex duct

Here is a picture of the water condensed on the retaining bar (the mesh filter cover is removed so you can see what is going on). water dripping from fan

It slides down this bar to the metal cover where it accumulates and then drips back to the range (or into the pot). The scrunched up paper towels are there to soak up the water before it drips back down. I have to change these regularly.

Typical boil- homebrewing

Typical boil during homebrewing..in fact this is the boil that caused dripping in photo above.

The damper is not closed. The duct has no blockage. The exhaust coming out of the duct is strong. It does this year round, hot outside, cold outside, a/c on heat on in house. Dry weather/humid weather.

Do I just need a better fan?

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    With large amounts of steam going up the pipe it is going to collect on the pipe and drip back down. A larger fan may prevent this if a strong fan is used and the fan left on until the water in the pipe drys out. I have seen ducting that had a collection baffle at the bottom. This had a small drain line. This was in a comercial kitchen with a very large vent but you may be able two find one that will fit your vent. – Ed Beal Jul 18 '16 at 13:56
  • By the way, though I show 2 pots in picture, it drips even with just one pot boiling. – Roberto Jul 18 '16 at 14:03
  • Ye gods - homebrew on a flat-top. I've been brewing on an electric stove for decades, but it had regular coils so I could install a "canning element" on one of the large burners. I want nothing to do with those glass-topped wonders. – Ecnerwal Jul 19 '16 at 2:21
  • The glasstop range works fine, not sure why you'd think otherwise. I have 3 cajun cookers for outside brewing when the weather cooperates. – Roberto Jul 19 '16 at 15:57
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More than 20 feet of flex pipe is a problem - 20 feet of flex pipe, uninsulated, sloped so it drains back into the fan is a huge problem.

Flex pipe has VERY high resistance to airflow compared with smooth duct. It should be avoided, or if its absolutely unavoidable it should only be used for very short sections where regular fittings will not work. I don't recall for sure but I believe that the stuff is normally forbidden on a range vent since it cannot be cleaned very well, and grease buildup is an issue. If the "flex pipe" in question is dryer vent hose it's VERY not suitable for range hood venting.

Long duct runs from fans venting moisture should be avoided, and if they cannot be avoided, the duct should turn to slope consistently towards the exit as soon as possible so that condensate runs out the exhaust. You may also need to increase the size of the duct to lower resistance.

Ducts carrying moisture should be insulated to reduce the condensation of moisture inside the duct.

Sure, you can slap a bigger fan on, but without solving the rest of your issues it may not help much.

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    I will get an HVAC contractor to put in a proper smooth walled duct line. The location of the kitchen makes it impossible to run a short section. Thanks! – Roberto Jul 18 '16 at 18:11
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    I note that the connector on that hood is 3-1/4x10 inches. Yet the duct would appear to be 4" - even 6" would be a reduction in area (28 sq inches .vs 32 square inches) but 4" is VERY much smaller at 12.5 sq inches. – Ecnerwal Jul 30 '16 at 1:35

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